This lab manual is our first response to the urgent need of a new set of experiments for the lab sessions of the General Science 111 course. It reflects two of our major efforts: a. To expand the scope of the experiment by including topics in the different disciplines. b. To implement the computer aided experiments. The experiments 3,11,12,13 and 14 are the newly added topics on astronomy, chemistry, biology and nuclear radiation. The experiments 2, 8, 9, 10, 11, 12 are the computer aided experiments. We do not, however, try to computerize those experiments which offer more direct experience to the students without a computer.

The instructions for the computerized experiments are written with reference to the software packages ULI Timer, Data logger 4.5 and Electricity 4.5 developed by Vernier Software Co.. Due changes have to be made if different software packages are used.

This manual would not have been possible without the materials provided to the author in laboratory manuals written by Dr. Lawrence K. Akers, Dr. Joel B. Davis, Dr. Mao-Zu Liu, Dr. Sam Nalley, Clayton R. Printz, Dr. Randolph S. Peterson, and the General Science 111 Laboratory Manual by Li-Hwa Huang and Ling Jun Wang. The author also wants to thank Mr. Bobby Thompson for his assistance with the lab equipment.

Ling Jun Wang

1. Human Response Time

2. Acceleration of Gravity

3. Measurement of Parallax

4. Projectile Motion

5. The Simple Pendulum

6. The Spring Constant

7. The Standing Waves on a String

8. Temperature Measurement and Energy Conservation

9. Ohm's Law

10. Resistors in Series and in Parallel

11. Acidic Battery

12. pH Measurements

13. Microscope Studies

14. Nuclear Radiation

Objective

To determine the human response time by using the free falling motion, and to study the phenomena with statistical errors.

Apparatus

Meter stick and masking tape.

Theory

The time between the stimulus and the response of a system is called the systemÕs response time. In this experiment one measures his or her own response time by catching a falling meter stick and measure the distance the meter stick traveled. Since the meter stick will be a freely falling body once released, the time of its fall (the response time) is related to the distance by

d = (1/2) g t2 (1)

where d is the distance, t is the time and g is the acceleration of gravity. Rearranging Eq. (1) yields

t = sqrt (2 d / g) (2)

where t is in seconds if d is measured in cm and g=980 cm/s2.

Procedure

Record your own response time only, although you need to help your partner to carry out the experiment.

1. Place two strips of masking tape at the edge of the table, with the two marks about two centimeters apart. These marks will help you to place your fingers at the same positions when repeating the experiment, thus reduce the statistical error.

2. your partner shall hold a meter stick vertically by the edge of the table, with the 20 cm mark at the table top level. Place your fingers on the masking tape marks without touching the meter stick.

3. Without warning, your partner shall drop the meter stick, and you shall try to catch it as soon as you notice the movement of the meter stick. Record the position of the meter stick where it is caught.

4. Repeat steps 2 to 3 twenty times. Record the position caught each time.

5. Switch positions with your partner and help him/her to measure his/her response time by repeating steps 2 to 4.

Data Analysis

1. Calculate the distance the meter stick falls each time.

2. Calculate the average distance the meter stick falls.

3. Calculate the average response time using Eq. (2).

4. Compare your response time to those of the rest of the class.

Suggested data table:

The starting distance: 20 cm.

Trial Position caught(cm) distance traveled(cm)

----------------------------------------------------------------------------

1

2

3

.

.

.

20

----------------------------------------------------------------------------

Average distance d =

Response time t =

Questions

1. What are the important error sources in this experiment?

2. How to reduce these errors?

Objective

To study the free falling motion and to measure the gravitational acceleration with a photo gate and computer.

Apparatus

Desk top computer, photo gate, ULI interface and picket fence. The experimental set-up is sketched in Figure 1.



Figure 1

Theory

The velocity of an object is defined as the time rate of the displacement:

v = Dx / Dt (1)

For a free-falling object, the velocity is given by

v(t) = vo + g t  (2)

where vo is the initial velocity and g is the gravitational acceleration.

In this experiment, the displacement Dx is fixed to be 0.05 m. The time interval Dt is measured automatically by the photo gate and the computer. The velocity v is calculated and plotted by the computer.

Now if we drop a picket fence, which is a long plexi glass plate painted with a series of opaque black strips, in the gravitational field with the strips in the horizontal direction, the photo gate will register the time interval it takes the picket fence to travel from one strip to the next. The time interval Dt becomes shorter and shorter as the picket fence runs faster and faster and the velocity of the falling picket fence becomes greater and greater. According to Eq.(2), the velocity should be proportional to the time elapsed, and the straight line is expected� of the plot of velocity vs. time. The slope of the straight line of the velocity plot in this experiment is equal to the gravitational acceleration g, which is know to be 9.8 m/s2.

Procedure

1. Turn on the computer and the interface box. Plug in photo gate to DG1 on interface box. Open the Vernier fold and then ULI Timer folder. Open First Experiment. Read the instruction on the screen.

2. Close the instruction window. Click the Start button and drop the picket fence through the photo gate with the bars oriented horizontally. Click the Stop button.

Caution: The picket fence is made of fragile plexiglass. DO NOT drop it to the floor. Receive the falling picket fence with a carton box or something soft to avoid damage.

3. Choose New Graph from the Window menu. A plot of Dt vs. t will be shown on the graph. How does it look? Make a hard copy of the graph.

4. Now try to get a plot of velocity vs. time. To do this, Click on and hold down the vertical axis label, and choose velocity from the menu by dropping the pointer on the item. A plot of the velocity vs. time will be shown on the graph. How does it look? Make a hard copy of the graph.

5. As indicated in the theory section, the acceleration is equal to the slope of the velocity plot. To obtain the acceleration, Choose both Regression Line and Statistics from the Graph menu. A straight line will be drawn to fit the velocity data points, and the slope and intercept will be shown on the graph. Record the value of the slope including the units. This is one of your experimental acceleration of gravity. How does it compare to the known value of 9.8 m/s2 ?

6. Repeat steps 2-5 five times. You will then have six experimental values of the gravitational acceleration. Find the average value and experimental error.

You do not have to make graphs for the repeated runs.

Questions

1. What are the important error sources in this experiment?

2. The intercept of the velocity plot is usually non-zero. Give two reasons for the non-zero intercept.

3. How is it going to affect your results if the strips of the picket fence is not kept horizontal in the free falling? You might want to find out the answer by purposely dropping the picket fence diagonally.

Attention:

1. Shut down your computer when finished. Go to file on tool bar and click on Quit. Do not save anything. Go to tool bar to Special on the tool bar and click on Shutdown. Turn off power if your computer requires it.

Turn off the interface box.

2. You still need to follow the format of a formal lab report even with the computer aided experiments.

Objective

To measure a distance from the observer to somewhere beyond reach, and to understand how the astronomical distances are measured.

Apparatus

Drawing table, linear graph papers, pins and meter stick.

Theory

Often times we need to measure the distance from us to somewhere beyond our reach. For example, a soldier might want to measure the distance from his canon to enemy's fort across the river; an astronomer wants to measure the distance from the Earth to a star. How can it be possible? We can do it by measuring the parallax as shown in Figure 1.



Suppose we want to know the distance from point A to point O, which we can not reach physically. We can measure the distance AB and the parallax angle a. According to trigonometry, the distance AO is given by:

AO = AB / tana (1)

if we keep the angle A to be 90o. The angle a can be measured with a protractor. How ever, a student protractor is not very accurate to measure large distances. An alternative is to measure the distances AB, AC and CD. If AB//CD, we have an expression, which is equivalent to Eq. (1) in principal, for the distance AO:

AO = AB * AC / (AB - CD) (2)

In practice, we can use a piece of linear graph paper, and the points A, B and C can be taken as the three corners of grid frame of the graph paper. The point D can be determined by aligning the points B, D and O with the pins.

Procedure

1. Place a piece of 18cm x 25 cm linear graph paper horizontally on a cardboard, laid at the end of the table away from the wall. Fix the paper with three pins at corners A, B and C of the grid frame of the graph paper. Make sure that all the pins are as vertical as possible.

2. Align the pins A and C to a vertical line O on the wall at the other end of the table. You can draw a line on a piece of paper and tape it on the wall, but do not draw lines on the wall.

3. Without moving the graph paper and the cardboard, place the forth pin in alignment with the pin B and the point O. Draw a straight line through the two pins, extending the line to meet the grid frame at the point D.

4. Measure the distance AB, AC and CD. You can use the graph paper as a ruler. The smallest division of a linear graph paper is 1 mm. Calculate the distance OB.

5. Now rotate the graph paper for 90o so that the 25 cm side is facing the distant object. Repeat the steps 3 and 4. Compare the results to that obtained in the step 4 and calculate the average distance.

6. Measure the distance OB directly using a meter stick. Compare this direct measurement with the average distance obtained above.

Data Analysis

(1) Calculate the distance AO by using Eq. (2).

(2) Calculate the parallax angle a by using the formula

a = tan-1[(AB-CD)/AC] (3)

(3) Calculate the distance L as follows:

L = BO = AB / sina (4)

(4) Repeat the same calculation steps (1) to (3) for the data obtained in the procedure step 5. Find the average distance Lav.

(5) Find the difference between the directly measured distance Ldir and Lav:

D = Ldir - Lav:

and calculate the percentage error:

%error = D / Ldir x 100 %

Questions:

(1) What is the relationship between the parallax angle and the distance?

(2) What are the error sources in this experiment?

(3) Do you have more confidence in the astronomical data after this lab?

(4) If the distance AB = 1 astronomical unit = 150 million km, and a distant star exhibits a parallax angle of one second (1/3600 degrees), what is the distance from us to the star? This distance is called one "parsec". At this small angle, tana = sina = a = 4.85 x 10-6 radians.

Objective

To understand the motion of a projectile in the gravitational field and measure the muzzle velocity of a projectile.

Apparatus

Spring gun with a ball projectile, target paper and carbon paper, meter stick and Scotch tape.

Theory

When a projectile is shot out horizontally in the gravitational field, its position can be described by the following two equations:

Vertical direction: Y = 0.5 g t2 (1)

Horizontal direction: X = v t (2)

where v is the initial muzzle velocity which remains constant through the flight. X and Y are, respectively, the horizontal and vertical coordinates of the projectile with the origin chosen at the muzzle of the gun (Figure 1). The ball travels a horizontal distance X in the same time it falls freely a vertical distance Y. The muzzle velocity can therefore be obtained from the above equations.

Procedure

1. Mount the spring gun horizontally on a table. Test fire the ball and notice the position where it lands.

2. Tape a large sheet of paper on the table where the ball lands on, and place a sheet of carbon paper over that paper, with the carbon side facing down.

3. Fire the gun six times and measure the horizontal distances from the gun to the landing spots. Find the average horizontal distance.

4. Measure the height of the muzzle from the table top.

Data Analysis

1. Calculate the time of flight using Eq. (1).

2. Calculate the muzzle velocity by substituting this flight time and the average horizontal distance into Eq. (2): vav = Xav /t.

3. Repeat the calculation of step 2 with the maximum distance in stead of the average distance. This will give the maximum muzzle velocity: Vmax=Xmax /t.

4. The difference between the maximum and the average muzzle velocities obtained in steps 2 and 3 gives an estimate of the statistical error of this measurement: D = Xmax - Xav .

5. Calculate the percentage error in the muzzle velocity:

% error = (D / Xav ) x 100 %.

Questions

1. What are the important error sources in this experiment? How to reduce these errors ?

2. Would the muzzle velocity be different if the mass of the projectile is changed ?

Objective

To determine the local gravitational acceleration and to investigate the relationship between the length of a pendulum and its oscillation period.

Apparatus

String, pendulum bob, timer and meter stick.

Theory

A simple pendulum consists of a bob suspended from a fixture by a light string of length L. The oscillation period T of a pendulum is the time it takes the bob to execute one complete cycle of oscillation. The amplitude is the maximum distance that the bob swings away from its equilibrium position. The period of a simple pendulum depends on its length and the acceleration of gravity, but independent of the mass of the bob. If L is much greater than the radius of the bob and the amplitude is small, the gravitational acceleration g can be expressed in terms of the length and the period of the pendulum:

g = 4 p2 L / T2 (1)

if the air resistance is ignored.

Procedure

1. Using a small amplitude, determine the time t for completing 10 cycles oscillation, with the pendulum length of 20 cm. Record the length and the corresponding time for 10 oscillations in the data table. Determine the period T by dividing the total time by 10.

2. Repeat the measurement with different pendulum lengths of 40, 60, 80 and 100 cm.

Data Analysis

1. Calculate the gravitational acceleration g by making use of Eq. (1).

2. Find the average acceleration of gravity and compare with the accepted value of 980 cm/s2. Find the per cent error.

Data Table

---------------------------------------------------------------------------

Length Total time for 10 cycles Period g L (cm) t (s) T (s) (cm/s2)

---------------------------------------------------------------------------

20

40

60

80

100

---------------------------------------------------------------------------

average g =

Dg =

% error in g = Dg /980 x 100 % =

Questions

1. How would you reduce the error in the time measurement?

2. Would any other shape be a better choice for the bob?

3. How does the period of a pendulum change when its length is quadrupled?

Objective

To determine the spring constant of a spiral spring.

Apparatus

Spring, set of weights, weight hanger and meter stick.

Theory

The spring constant is a measure of the stiffness of a spring. If the spring is hung vertically and a mass m is attached to the lower end of the spring, the spring stretches a distance d from its initial position under the action of the "load" weight

W = mg (1)

Since the weight w is downward, it must be balanced by the upward spring force when the system is at rest, i.e.,

F = W = mg (2)

According to HookeÕs Law the force on the spring is directly proportional to the elongation within the elastic limit (the maximum stretch a spring can experience without becoming permanently deformed):

F = k d (3)

where F is the force, k is the spring constant and d is the elongation.

Procedure

1. Measure the original length L0 of the spring when hung vertically.

2. Hang a 200 gram mass (the mass of the 50 g hanger must be counted) from the spring and measure the length L of the stretched spring. Record the length and the weight.

3. Repeat step 2 in 50 g increments.

Data Analysis

1. Calculate the elongation using d = L - L0.

2. Calculate the forces F using Eq. (2), where m is in kg, g=9.8 m/s2 and F is in newtons.

3. Calculate the spring constant k for each mass.

4. Calculate the average spring constant and the percent error.

Data Table

L0 = ________ m

------------------------------------------------------------------------

Mass Force Length Elongation k

(kg) (N) L (m) d=L-L0 (m) (N/m)

------------------------------------------------------------------------

0.200

0.250

0.300

0.350

0.400

0.450

------------------------------------------------------------------------

average kav =

maximum kmax =

Dk = kmax - kav =

% error in g = Dk /kav x 100 % =

Objective

To verify the relationship between the wave velocity, the wavelength and the frequency for a transverse wave, and determine the stringÕs linear mass density.

Apparatus

Magnetic vibrator, string, pulley, meter stick, set of weights and balance.

Theory

The velocity v of a transverse wave on a stretched string depends on the tension F in the string and the linear mass density m (the mass per unit length). The relationship is given by

F = m v2 (1)

The wave velocity is given by

v = l f (2)

where l is the wavelength and f is the frequency of the vibration. f = 120 Hz in this experiment. The wavelength can be most easily measured in a standing wave state.

If the stretched string is clamped at both ends, traveling waves will be reflected from the fixed ends back and forth, creating waves traveling in both directions. The incident and the reflected waves will be superposed together. If the distance between the fixed ends of the string is an integer number of half wavelength, a standing wave will be produced and the string will look like a chain of vibrating spindles. The positions with the largest amplitudes are called antinodes and the positions at rest are the nodes. The distance between the successive nodes is equal to one half wavelength.

Procedure

1. Clamp the oscillator to the table. Attach the string to the oscillator and stretch it over the pulley with a weight hanger. Measure the length L of the string from the fixture to the top of the pulley.

2. Turn on the oscillator.

3. Adjust the tension on the string by adding weights until a standing wave is produced with at least five segments. The length of each segment is equal to one half of the wavelength, which can be obtained by dividing the string length L the number of segments.

4. Record the total weight hung from the string, including the weight of the hanger.

5. Increase the tension by adding more weights until another standing wave is established with one less segments. Measure and record the segment length (the half wavelength) and the weight. Repeat this until the tension is great enough to establish a standing wave with two segments only.

Data Analysis

1. Calculate the tension for each standing wave using F=mg.

2. Calculate the wavelength of each standing wave.

3. Calculate the wave velocity v for each standing wave using Eq. 2. The frequency f of the vibrator is 120 s-1.

4. Calculate the linear mass density m by making use of Eq. 1.

5. Calculate the average mass density and the percent error.

Data Table

L = _____ m, f = 120 s-1.

------------------------------------------------------------------------

Number of Mass wavelength velocity m

segments (kg) l (m) v (m/s) (kg/m)

------------------------------------------------------------------------

5

4

3

2

------------------------------------------------------------------------

average mav =

maximum mmax =

Dm = mmax - mav =

% error in m = Dm /mav x 100 % =

Objective

To familiarize with computer interface and data analysis. To study energy conservation law by measuring the hear transfer during the processes of melting of ice and mixing of water at different temperatures.

Apparatus

Desk top computer, temperature probe, thermometer, balance, Styrofoam cup.

Theory

When a piece of ice is melted in water, it will absorb energy from the water. The heat energy released by the "warm" water at the room temperature is equal to

Q = C mw (To - Tf ) (Eq.1)

where mw is the mass of the water is the cup and To is the initial temperature of it. C is the specific heat of water which is equal to 1 cal./(g oC). The energy absorbed in melting the ice is equal to

QÕ = Hf mi (Eq.2)

where Hf = 80 cal./g is the latent heat of fusion of ice, and mi is the mass of the ice. The energy absorbed in raising the temperature of the cold water of melted ice to the equilibrium temperature Tf is equal to

Q" = C mi Tf (Eq.3)

According to energy conservation law, Q must be equal to the sum of QÕ and Q" if there is no heat from the air leaking into the cup. However, the leak may be significant if the ice is big and takes a long time to melt.

Procedure

1. Turn on the computer and the interface box. Open the application Data Logger 4.5. Choose "One Graph" from the Display menu.

2. Choose Axes from Display menu. Set the vertical axis scale from 0 to 30. Set the horizontal scale from 0 to 1000. Choose Labels & Units from Display menu. Type "Temperature" for the long name of Port 1, T for the short name, and C for the units.

3. Open Calibrate from Collect menu to calibrate the temperature sensor. The computer will then ask you "How would you like to calibrate the probes?" Respond by clicking "Calibrate Now". Choose the port number to which your probe is hooked up.

l4. You need two temperatures to do calibration. The water temperature and the ice point are two convenient temperatures for this purpose. Immerse both the probe and the thermometer in the water for about two minutes for the temperature to stabilize. Respond to the computer with the temperature as read from the thermometer. This is the high temperature for calibration. Follow the instructions in the dialogue window to calibrate your probe. Then let the tip of your probe touch a piece of ice for about two minutes. The probe is supposed to reach zero oC. This is the low temperature for calibration. Respond to the computer with this temperature to complete your calibration.

5. Measure and record the mass of the Styrofoam cup.

6. Fill in about 100 ml (two thirds of a cup) of water at room temperature and measure the mass again. Subtract the mass of the cup from the total mass to get the mass of the water.

7. Stick the temperature sensor in the water and click "Start" button to start scanning the temperature. The temperature value and the time elapsed will be shown on the graph. It usually takes the probe about 45 seconds to reach the equilibrium, as can be seen from the movement of the red cursor on the graph. Record this temperature T0 of the "warm" water.

8. Leave the probe in the water and put a piece of ice in, and stir gently with the probe until the ice is completely melted. It is extremely important to keep the ice dry, or your result will not be accurate. Do not use crushed ice! Notice the temperature curve is bending down and reach a minimum value when the ice is completely melted. The temperature will then soon raise due to absorption of heat from the air at room temperature. The minimum temperature is therefore taken as the final temperature Tf of the mixture. Click Stop button a few minutes after you have seen the minimum of the curve.

9. Record the minimum temperature. To read the temperature accurately, click Analyze on top tool bar and chose Analyze Data A. A vertical cursor bar will show up. Move the vertical bar to the minimum point on the temperature curve by using the arrow keys on the key board. The temperature value will be shown at the bottom of the screen.

10. Take out the probe and measure the total mass of the mixture to find the mass of the ice cube, mi.

Data Analysis

Design your own data table to record the masses and the temperatures.

Show the detailed calculation in your report.

1. Calculate the heat released by the "warm" water using Eq.1.

2. Calculate the heat absorbed QÕ and Q" using Eqs. 2 and 3. The sum of these two items is the total heat absorbed.

3. Calculate the difference between the heat absorbed and the heat released. Is the heat released greater or smaller than the heat absorbed? Why? Calculate the percentage error and comment on the error sources.

4. Include the temperature graph in your lab report.

Questions

1. According to your experiment, is energy conserved within experimental error? (The error of measurement in this kind of experiments should be less than 10%.)

2. If there is a difference in the measured released heat and absorbed heat, which one is greater? Why? What are the possible error sources?

3. Why is the room temperature chosen as the initial "warm" temperature?

Attention:

Shut down your computer when finished. Go to file on tool bar and click on Quit. Do not save anything. Go to tool bar to Special and click on Shutdown. Turn off power if your computer requires it.

Objective

To familiarize with computer interface and data analysis. To study energy conservation law by measuring the hear transfer during the processes of melting of ice and mixing of water at different temperatures.

Apparatus

Desk top computer, temperature probe, thermometer, balance, Styrofoam cup.

Theory

When a piece of ice is melted in water, it will absorb energy from the water. The heat energy released by the "warm" water at the room temperature is equal to

Q = C mw (To - Tf ) (Eq.1)

where mw is the mass of the water is the cup and To is the initial temperature of it. C is the specific heat of water which is equal to 1 cal./(g oC). The energy absorbed in melting the ice is equal to

QÕ = Hf mi (Eq.2)

where Hf = 80 cal./g is the latent heat of fusion of ice, and mi is the mass of the ice. The energy absorbed in raising the temperature of the cold water of melted ice to the equilibrium temperature Tf is equal to

Q" = C mi Tf (Eq.3)

According to energy conservation law, Q must be equal to the sum of QÕ and Q" if there is no heat from the air leaking into the cup. However, the leak may be significant if the ice is big and takes a long time to melt.

Procedure

1. Turn on the computer and the interface box. Open the application Logger Pro from Vernier folder. Choose "Open" from the File menu. Click Expfiles in the Derectories box. Open Physicl file and open expo8.mbl.

2. Set the vertical axis scale from 0 to 30. Set the horizontal scale from 0 to 1000 second.

3. Open Calibrate from Experiment menu to calibrate the temperature sensor. Click "Perform Now". Choose the port number to which your probe is hooked up.

l4. You need two temperatures to do calibration. The water temperature and the ice point are two convenient temperatures for this purpose. Immerse both the probe and the thermometer in the water for about two minutes for the temperature to stabilize. Respond to the computer with the temperature as read from the thermometer. This is the high temperature for calibration. Follow the instructions in the dialogue window to calibrate your probe. Then let the tip of your probe touch a piece of ice for about two minutes. The probe is supposed to reach zero oC. This is the low temperature for calibration. Respond to the computer with this temperature to complete your calibration.

5. Measure and record the mass of the Styrofoam cup.

6. Fill in about 100 ml (two thirds of a cup) of water at room temperature and measure the mass again. Subtract the mass of the cup from the total mass to get the mass of the water.

7. Stick the temperature sensor in the water and click "Collect" button to start scanning the temperature. The temperature value and the time elapsed will be shown on the graph. It usually takes the probe about 45 seconds to reach the equilibrium, as can be seen from the movement of the red cursor on the graph. Record this temperature T0 of the "warm" water.

8. Leave the probe in the water and put a piece of ice in, and stir gently with the probe until the ice is completely melted. It is extremely important to keep the ice dry, or your result will not be accurate. Do not use crushed ice! Notice the temperature curve is bending down and reach a minimum value when the ice is completely melted. The temperature will then soon raise due to absorption of heat from the air at room temperature. The minimum temperature is therefore taken as the final temperature Tf of the mixture. Click Stop a few minutes after you have seen the minimum of the curve.

9. Record the minimum temperature. To read the temperature accurately, click Analyze on top tool bar and click Examine. A vertical cursor bar will show up. Move the vertical bar to the minimum point on the temperature curve by using the arrow keys on the key board. The temperature value will be shown at the bottom of the screen.

10. Take out the probe and measure the total mass of the mixture to find the mass of the ice cube, mi.

Data Analysis

Design your own data table to record the masses and the temperatures.

Show the detailed calculation in your report.

1. Calculate the heat released by the "warm" water using Eq.1.

2. Calculate the heat absorbed QÕ and Q" using Eqs. 2 and 3. The sum of these two items is the total heat absorbed.

3. Calculate the difference between the heat absorbed and the heat released. Is the heat released greater or smaller than the heat absorbed? Why? Calculate the percentage error and comment on the error sources.

4. Include the temperature graph in your lab report.

Questions

1. According to your experiment, is energy conserved within experimental error? (The error of measurement in this kind of experiments should be less than 10%.)

2. If there is a difference in the measured released heat and absorbed heat, which one is greater? Why? What are the possible error sources?

3. Why is the room temperature chosen as the initial "warm" temperature?

Attention:

Shut down your computer when finished. Go to file on tool bar and click on Quit. Do not save anything. Go to tool bar to Special and click on Shutdown. Turn off power if your computer requires it.

Objective

To verify OhmÕs law with the computer aided circuit.

Apparatus

Desk top computer, ULI interface, Dual Channel Amplifier, voltage probe, current probe, resistor, digital voltmeter and variable voltage source.

Theory

OhmÕs law is one of the most important law which states that the ratio of the voltage across a resistor is proportional to the current passing through it:

V = R I (1)

where V is the voltage in volts, I is the current in amperes and R is the resistance in ohms. A graph of V vs. I should yield a straight line for a resistor, the slope of the straight line being the resistance of it. The experimental set up is sketched below.



Procedure

1. Construct a circuit sketched in Fig. 1 with a �100 W resistor. Connect the voltage probe to Probe 1 and the current probe to Probe 2 of the Amplifier. Connect DIN 1 and DIN 2 cables of the Amplifier to the corresponding sockets DIN 1 and DIN 2 of the interface box. Turn on the voltage power supply, the computer and the ULI interface box.

2. Open the application Electricity 4.5. Choose "One Graph" from the Display manual. Set the time scale from 0 to 1000 seconds. You can do this by click the scale on the time axis and retype in the number.

2. Choose Voltage for the vertical axis. You can do this by clicking on the axis label. Set the scale from 0 to 5 volts. Choose Current for the horizontal axis and set the scale from 0 to 0.1 amperes.

3. Click "Start" button to start data taking. Keep on varying the output voltage between zero and 5 volts.� The cursor should move on the screen about a straight line, with some deviation due to noise. Click on Stop when you have made a few repeated tracks back and forth.

4. Click fit from Analyze manual. Choose linear y=b0 + b1 * x. Click Try Fit button, and Maintain Fit to get back to the graph screen. The values of b0 and b1 are shown on the right top corner of the graph. b1 is the resistance in kW. Multiply b1 by 1000 to get the experimental resistance in W. b0 is expected to be zero, or a very small value.

Data Analysis

Compare your experimental resistance value to the nominal value. Are they close? Calculate the percentage error. Show the detailed calculation in your report. Include a sketch of the graph in your lab report.

Objective

To verify expression for equivalent resistance in series and in parallel circuits using OhmÕs law.

Apparatus

Desk top computer, ULI interface, Dual Channel Amplifier, voltage probe, current probe, two different resistors (100 ~ 200 ohms), digital voltmeter and variable voltage source.

Theory

The resistors can be combined in two different ways, either in series or in parallel. Figures 1 and 2 show the series and parallel connections respectively.

Figure 1. Resistors in series Figure 2. Resistors in parallel

It can be shown theoretically that the two resistors in series can be replaced with a single resistor having a resistance equal to the sum of the two:

Req = R1 + R2 (1)

Likewise, the two resistors in parallel can be replaced with a single resistor. However, the formula for calculating the equivalent resistance is different:

Req = (R1R2)/(R1 + R2) (2)

Procedure

1. Referring to the experimental procedures of Experiment 9, measure the resistance R1 and R2 individually.

2. Measure the equivalent resistance of the two resistors in series as sketched in Fig. 1.

3. Measure the equivalent resistance of the two resistors in parallel as sketched in Fig. 2.

Data Analysis

Check and see if the equations 1 and 2 are valid within certain experimental error. Are the two sides of the equations close? Calculate the percentage errors for both the series and parallel configurations. Show the detailed calculation in your report.

Attention:

Shut down your computer when finished. Go to file on tool bar and click on Quit. Do not save anything. Go to tool bar to Special and click on Shutdown. Turn off power if your computer requires it.

Objective

To study the electromotive force of battery.

Apparatus

Desk top computer, ULI interface, Dual Channel Amplifier, voltage probe, voltmeter, dry battery, small beaker, lemon juice, orange juice, vinegar, electrodes (zinc, copper, aluminum, magnesium, carbon, iron), connecting wires.

Theory

To supply continuous current in a circuit, a device that can move the electric charge against the electric field must be equipped. The electric battery is one of such device, and the ability to move the electric charge against the electric field is called the electromotive force. It is clear then that the electromotive force can not be electrostatic in origin. A battery uses the "chemical force" as the electromotive force.



Figure 1 shows the structure of a electric battery. Two electrodes, zinc and carbon, for example, are immersed in the electrolyte, say, a lemon juice (the reason that the battery charge is sometimes called "juice"). The electrolyte actively dissolves the zinc causes the positive ion to move towards the carbon electrode. The zinc thus becomes the negative electrode and the carbon positive. If the two electrodes are made of the same material, we should not expect any voltage coming out of the device as the electromotive force of the two electrodes cancel each other. If the two electrodes are made of different material, however, we should expect some "net gain" of electromotive force to show up at the terminal of the battery. The effect of the different combination of the electrodes is one of the subjects of this study.

Procedure

1. Set up the experiment sketched in Fig.1. Fill in half a beaker of lemon juice. Use zinc and carbon as�the electrodes.

2. Turn on the computer and the ULI interface box. Open the application Data Logger 4.5. Choose "One Graph" from Display menu.

3. Choose Axes from Display menu. Set the vertical axis scale from 0 to 2. Set the horizontal scale from 0 to 1000. Choose Labels & Units from Display menu. Type "Voltage" for the long name of port 1, V for the short name, and V for the units.

4. Open Calibrate from Collect menu to calibrate the voltage sensor. The computer will then ask you "How would you like to calibrate the probes?" Respond by clicking "Calibrate Now". Choose Port 1 to which your voltage probe is hooked up.

5. You need two values to calibrate the probe. Disconnect the voltage probe from the circuit and short the two leads. Wait for a few seconds for the probe to stabilize. Respond to the computer with the value zero. Then measure the voltage of a dry battery with both the computer and a voltmeter. Use this voltage to calibrate your probe, following the instructions in the dialogue window. Now clip the leads back on the electrodes of your set-up.

6. Now set the vertical scale from 0 to 1. Click "Start" button to start data taking. The cursor will trace a line on the screen as time goes on. Notice the voltage change. Is the voltage increasing or decreasing? Measure the voltage change in 1000 seconds (16.7 minutes). What happens to the voltage if the probe leads are switched? Which electrode is positive and which is negative? Record the polarity of the electrodes.

7. Observe the bubbles developing around the electrodes. Try to shake off the bubbles from the electrodes gently. How does the voltage change? Does it give you any hint?

8. Use the same material for both electrodes. What is the voltage? Why? 9. Use different combinations of the electrodes and measure the corresponding voltages, and record the polarity of the electrodes for each combination. You do not have to spend a lot of time to get the whole curve for all these combinations. The voltage can be read from the bottom of the screen. The voltage should be stabilized in a few seconds.

What combination gives the highest voltage? What gives the lowest?

Line up all the materials used for electrodes in such a way that for any pair of materials in the list, the one on the left in the list makes a positive electrode while the one on the right makes a negative one.

10. Measure the voltage again with the best combination of electrodes. Then dilute the juice with distilled water and measure the voltage again. What do you find out?

11. Now change the distance between the electrodes. Do you notice a significant difference in voltage?

12. Again with the best set of electrodes, measure the voltage with the different electrolyte juice. The stronger acid should give higher voltage. Based on this a pH sensor which measures the hydrogen ion concentration can be designed. According to you voltage measurement, what electrolyte is the strongest acid used in this experiment?

Data and Conclusion

Record all the measurement results described in the procedure and answer all the pertinent question.

Clean up every thing and shut down the computer properly.

Objective

To study the electromotive force of battery.

Apparatus

Desk top computer, ULI interface, Dual Channel Amplifier, voltage probe, voltmeter, dry battery, small beaker, lemon juice, orange juice, vinegar, electrodes (zinc, copper, aluminum, magnesium, carbon, iron), connecting wires.

Theory

To supply continuous current in a circuit, a device that can move the electric charge against the electric field must be equipped. The electric battery is one of such device, and the ability to move the electric charge against the electric field is called the electromotive force. It is clear then that the electromotive force can not be electrostatic in origin. A battery uses the "chemical force" as the electromotive force.



Figure 1 shows the structure of a electric battery. Two electrodes, zinc and carbon, for example, are immersed in the electrolyte, say, a lemon juice (the reason that the battery charge is sometimes called "juice"). The electrolyte actively dissolves the zinc causes the positive ion to move towards the carbon electrode. The zinc thus becomes the negative electrode and the carbon positive. If the two electrodes are made of the same material, we should not expect any voltage coming out of the device as the electromotive force of the two electrodes cancel each other. If the two electrodes are made of different material, however, we should expect some "net gain" of electromotive force to show up at the terminal of the battery. The effect of the different combination of the electrodes is one of the subjects of this study.

Procedure

1. Set up the experiment sketched in Fig.1. Fill in half a beaker of lemon juice. Use zinc and carbon as the electrodes.

2. Turn on the computer and the ULI interface box. Open the application LoggerPro.

3. Set the vertical axis scale from 0 to 2. You can do this by clicking on the exsisting scale number of the vertical axis. Set the horizontal scale from 0 to 1000 in the same fasion. The vertical axis should be labled "Voltage" or "Potential", and the horizontal axis should be labled "Time". You can do this again by clicking the coresponding lables by the axis.

4. Open Calibrate from Experiment menu to calibrate the voltage sensor. Click Perform Now to start calibration.

5. You need two values to calibrate the probe. Disconnect the voltage probe from the circuit and short the two leads. Wait for a few seconds for the probe to stabilize. Respond to the computer with the value zero for Value One. Click OK button and the computer will switch to the second value. Then measure the voltage of a dry battery with both the computer and a voltmeter. Use this voltage for Value Two. Click OK button to end calibration. Now clip the leads back on the electrodes of your set-up.

6. Now set the vertical scale from 0 to 1. Click "Collect" button to start data taking. The cursor will trace a line on the screen as time goes on. Notice the voltage change. Is the voltage increasing or decreasing? Measure the voltage change in 1000 seconds (16.7 minutes). What happens to the voltage if the probe leads are switched? Which electrode is positive and which is negative? Record the polarity of the electrodes.

7. Observe the bubbles developing around the electrodes. Try to shake off the bubbles from the electrodes gently. How does the voltage change? Does it give you any hint?

8. Use the same material for both electrodes. What is the voltage? Why? 9. Use different combinations of the electrodes and measure the corresponding voltages, and record the polarity of the electrodes for each combination. You do not have to spend a lot of time to get the whole curve for all these combinations. The voltage can be read from the bottom of the screen. The voltage should be stabilized in a few seconds.

What combination gives the highest voltage? What gives the lowest?

Line up all the materials used for electrodes in such a way that for any pair of materials in the list, the one on the left in the list makes a positive electrode while the one on the right makes a negative one.

10. Measure the voltage again with the best combination of electrodes. Then dilute the juice with distilled water and measure the voltage again. What do you find out?

11. Now change the distance between the electrodes. Do you notice a significant difference in voltage?

12. Again with the best set of electrodes, measure the voltage with the different electrolyte juice. The stronger acid should give higher voltage. Based on this a pH sensor which measures the hydrogen ion concentration can be designed. According to you voltage measurement, what electrolyte is the strongest acid used in this experiment?

Data and Conclusion

Record all the measurement results described in the procedure and answer all the pertinent question.

Clean up every thing and shut down the computer properly.

Objective

To learn the principle and technique of pH measurements.

Apparatus

Desk top computer, ULI interface, pH sensor and amplifier, beakers and test tubes, chemical samples (vinegar, lemon juice, apple juice, soft drink, baking soda, detergent, table salt, distilled water, natural water, soil).

Theory

Acidity is an important parameter in chemistry, medical science as well as in agriculture. The acidity of a solution is measured by the concentration of the H+ ions, which spans over 14 orders of magnitude. The strongest acids have H+ ion concentrations in the order of ten moles per liter, while the strongest bases have the H+ ion concentration in the order of 10-15 moles per liter. The neutral distilled and deionized water has a H+ ion concentration of 10-7 moles per liter. The pH value of a solution is then defined to be the exponent of the negative power to which 10 is raised when powers of 10 are used to express the concentration:

pH = Log10(C) (1)

where C is the mole concentration of the H+ ions. Apparently, the neutral water or salt solutions have pH value of 7; The acids have pH values smaller than 7; and bases have pH values greater than 7.

Procedure

1. Clean all the beakers and test tubes with the tap water, and rinse with the distilled water. Dry with paper towel.

2. Prepare the pH electrode for use. Remove the storage bottle from the electrode by loosening the lid. Place the storage bottle in a safe place where it will not be tipped over accidentally. Slide the lid upward on the probe body, exposing the O-ring, slide or roll the O-ring down the body of the probe to remove it, then remove the cap. Thoroughly rinse the lower section of the probe, especially the region of the bulb�R, using distilled water. If you notice air bubbles in the reference reservoir, shake the electrode in a downward motion until the bubble disappears.

3. Connect the pH electrode to the Vernier pH Amplifier box, and connect to box to your lab interface.

4. Turn on the computer and the ULI interface box. Open Experiment 27 from Chemistry w/Computer file.

5. Open Calibrate from Collect menu to calibrate the voltage sensor. The computer will then ask you "How would you like to calibrate the probes?" Respond by clicking "Calibrate Now". Choose port 1 to which your voltage probe is hooked up.

Calibrate the pH electrode by using the 2-point calibration option of the Vernier data collection program. Rinse the tip of the electrode in distilled water. Place the electrode into one of the buffer�solutions (e.g., pH4). When the voltage reading on screen stabilizes, enter a pH value 4. Rinse the electrode and place it into a second buffer solution pH7. When the voltage stabilizes, enter pH value 7.

6. Set the vertical axis scale from 0 to 15. Set the horizontal scale from 0 to 1000. Choose Labels & Units from Display menu. Type "Acidity" for the long name of port 1, pH for the short name, and pH for the units.

7. Measure and record the pH values of the samples supplied by your instructor. Remember to wash and rinse the pH electrode thoroughly with the distilled water each time you have finished measuring pH value of one sample.

8. Shut down the equipment properly. Clean and store the pH probe in the storage solution bottle in the reversed order as described in step 2.

Objective

To learn the principle and technique of pH measurements.

Apparatus

Desk top computer, ULI interface, pH sensor and amplifier, beakers and test tubes, chemical samples (vinegar, lemon juice, apple juice, soft drink, baking soda, detergent, table salt, distilled water, natural water, soil).

Theory

Acidity is an important parameter in chemistry, medical science as well as in agriculture. The acidity of a solution is measured by the concentration of the H+ ions, which spans over 14 orders of magnitude. The strongest acids have H+ ion concentrations in the order of ten moles per liter, while the strongest bases have the H+ ion concentration in the order of 10-15 moles per liter. The neutral distilled and deionized water has a H+ ion concentration of 10-7 moles per liter. The pH value of a solution is then defined to be the exponent of the negative power to which 10 is raised when powers of 10 are used to express the concentration:

pH = Log10(C) (1)

where C is the mole concentration of the H+ ions. Apparently, the neutral water or salt solutions have pH value of 7; The acids have pH values smaller than 7; and bases have pH values greater than 7.

Procedure

1. Clean all the beakers and test tubes with the tap water, and rinse with the distilled water. Dry with paper towel.

2. Prepare the pH electrode for use. Remove the storage bottle from the electrode by loosening the lid. Place the storage bottle in a safe place where it will not be tipped over accidentally. Slide the lid upward on the probe body, exposing the O-ring, slide or roll the O-ring down the body of the probe to remove it, then remove the cap. Thoroughly rinse the lower section of the probe, especially the region of the bulb�R, using distilled water. If you notice air bubbles in the reference reservoir, shake the electrode in a downward motion until the bubble disappears.

3. Connect the pH electrode to the Vernier pH Amplifier box, and connect to box to your lab interface.

4. Turn on the computer and the ULI interface box. Open LoggrPro from the folder Vernier Software, and click Open from the File menu. Open Experiment 27 from the folder ~Chemist.

5. To calibrate, open Calibrate from Experiment menu. The computer will show a screen of "Sensor Properties". Choose port 1 to which your voltage probe is hooked up. Click the button "Perform Now" to start calibration.

Calibrate the pH electrode by using the 2-point calibration option of the Vernier data collection program. Rinse the tip of the electrode in distilled water. Place the electrode into distilled water. Wait till the voltage reading is stablized (You may need to wait for at least 40 seconds) . Enter the value 7 and click the button Keep. The program will switch to the second calibration value. Rinse the tip of the electrode well in distilled water. Place the electrode into a buffer�solution (e.g., pH4). When the voltage reading stabilizes, enter a pH value 4. Rinse the electrode well before using it for any measurement.

6. Measure and record the pH values of the samples supplied by your instructor. Remember to wash and rinse the pH electrode thoroughly with the distilled water each time you have finished measuring pH value of one sample.

7. Shut down the equipment properly. Clean and store the pH probe in the storage solution bottle in the reversed order as described in step 2.

Objective

To learn how to use a microscope to study the various samples.

Apparatus

Microscope, slides and samples (onionskin, salt, mica, Styrofoam).

Theory

The microscope is used to examine very small objects. It can be said that microscopes are our eyes to see the microscopic world, and are responsible for many important discoveries in sciences. An optical microscope consists of two converging lenses (Figure 1). The lens near the object is called the objective, while the one near the eye is called the eyepiece or ocular. When the object sample is placed at the right position so that a clear image is seen through the eyepiece, we say that the microscope is focused. The amplification of an optical microscope is determined by the focal lengths of the two lenses and the tube length of the microscope itself. In this experiment, we will use a microscope with three objectives of different focal length, and therefore, different magnifications (4x, 10x and 40x). The objective with smaller magnification allows one to locate the objective easily, and it is the shortest in size. The longest objective provides the greatest magnification.



Procedure

1. Plug the power cord of the microscope into the line voltage socket. Turn on the power switch on the base of the microscope. You can change the objectives by rotating the mount. Use the 4X objective (the shortest) first.

2. Place the slide with onion skin sample on the sample stage and clip it on. Make sure the onion skin is on the top surface of the slide! Position the sample at the center of the light hole. Look into the microscope while focusing the objective. The focusing is done by turning the knob to adjust the objective distance. Make sure that the objective is not touching the sample.

3. When the microscope is well focused and a clear image of the sample is seen, you can then switch to the objectives with higher magnification (10x or 40x). The 40x objective is the longest one and the objective distance is very short. The tip of the 40x objective is almost touching the sample slide. Extra caution has to be exercised to avoid damage to the objective and the sample slide.

4. When the sample is well focused under the higher magnification objective, draw a picture of the tissue cells of the onion skin. The advanced microscopes are equipped with a camera to take photographs directly.

5. Now apply a small drop of saturated salt solution on the same slide near the onion skin. Slide the slide gingerly to position the salt solution under the objective. Look into the microscope and observe the change. As the water is vaporizing, the salt should be crystallized and seen through the microscope. Sketch a picture of the salt crystal. How does it look like?

6. Switch to the 4X objective and the mica sample. Repeat steps 2-4 and sketch a picture of the mica crystal texture. You might want to dye the mica sample with some ink for better rendition of the picture.

Objective

1. To study the nuclear radiation through emitting the b and g particles; (The a radiation sources are not readily available).

2. To investigate the interaction of these particles with matters;

3. To learn the operation of the Geiger-Mueller counter.

4. To learn how to use a micrometer.

Apparatus

Geiger-Muller tube and counter, b (strontium 90) and g (cobalt 60) sources, sets of plastic, aluminum and lead absorbers, micrometer.

Theory

The nuclear radiation are classified into three categories: a, b and g rays. The a ray is a beam of helium nucleus with charge +2 and mass 4; The b ray is a beam of electrons with charge -1 and a mass that is about eight thousand times lighter than the mass of an a particle; The g ray is a chargeless and massless light wave. The g ray and X-ray are essentially the same thing -- both are electromagnetic waves with very short wavelength, and are highly penetrating. In terms of penetrating power, the a particles are the softest due to its heavy mass,�and the g rays are the hardest due to its zero mass and electrical neutrality. The a radiation can be stopped by a piece of paper, and the b radiation can be stopped by a thin film of metal (~ 1 mm thick), but the g radiation can penetrate through a few centimeters of lead!

When a nuclear radiation (a, b and g rays) passes through a layer of absorber with thickness x, its ray intensity will reduce from its original value I0 to some smaller value I. The relationship is given by

I = I0 exp[- x / x0] (1)

where x0 is called the range of the ray in that matter. From Eq. (1) we know that the range x0 is the thickness at which the ray intensity reduces to 37%. If we plot the extenuated intensity I as a function of the thickness of the absorber, an exponential curve should yield, and the range x0 can be obtained from the exponential curve.

Procedure

1. Turn on the Geiger-Muller counter. Set the high voltage to 500 volts. Reset the counter and turn off the Test button. Set the timer to 2 minutes.

2. Take the background counts of the cosmic ray for two minutes, keeping all the radiation sources away from the GM tube. This background counts must be subtracted from the radiation counts throughout the whole experiment.

3. Place a beta source at the lowest position of the sample holder. Count for two minutes and record the counts. This is the initial ray intensity I0 when there is practically no shielding material between the source and the counter.

4. Insert plastic absorbers of different thicknesses between the beta source and the GM tube. The thickness of the absorber can be measured with the micrometer. Count for two minutes and record the counts corresponding to the different thicknesses. How thick a plastic is needed to shield the beta radiation to practically zero?

5. Place a thin piece of lead absorber between the beta source and GM tube. Count for two minutes. How much beta radiation has penetrated through the lead absorber? Is lead a better shielding as compared to the plastics?

6. Replace with a gamma source and count for two minutes. Record the counts. The gamma source usually has a beta component. The counts obtained is the total of both the beta and the gamma radiation.

7. Cover the source with a plastic absorber of 6 mm and count again. It should be able to get rid of all the beta radiation and allow the gamma radiation to pass. Is the number of counts much smaller than that obtained in step 9? The difference measures the beta radiation of the source.

8. Find the thickness of lead absorber enough to shield the gamma ray completely.

Data Analysis

1. Plot the intensity of the beta ray as a function of the thickness of the plastic absorbers. Connect the data points with a smooth curve. This is the exponential attenuation curve.

2. Draw a horizontal line at the 37% of the initial ray intensity I0. The intercept of this line and the exponential curve indicates the range of the beta ray in this absorber. Report the range.

Data Table

Background counts = ___________________

Alpha ray intensity = ___________________

Attenuation of beta ray by plastic absorbers:

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Thickness Total counts intensity=Total-background

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0

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Total counts of gamma source = _____________

Net gamma counts with plastic cover = _____________

Thickness of lead to shield the gamma ray = ______________