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Posted: April 13th, 2023
Physics Lab And Report
Materials
Read through the procedures listed in the exercises on the next pages before beginning. Then, gather all of the materials listed below and begin Exercise 1.
Note: The packaging and/or materials in your kit may differ slightly in appearance from images in the experimental procedures.
Student Supplied
3 Binder clip
1 Camera, digital or smartphone
1 Roll of clear tape
1 Sheet of white paper
1 Flashlight
Science Interactive Supplied
1 Digital multimeter
2 Jumper cable
1 Pair of safety goggles
1 Photocell
3 Polarizing card
1 Protractor
1 Ruler
Exercise 2
Quantitative Exploration of Polarized Light
In this exercise, you will use a digital multimeter to measure the resistance of a photocell when light passes through a series of polarizing filters. You will calculate light intensity and graph the behavior of light transmission through polarizing filters.
Procedure
Part 1: Experimental Setup and Background Intensity
1. Gather the digital multimeter (DMM), photocell, jumper cables, ruler, tape, flashlight, protractor, paper, binder clips, safety goggles, and polarizing cards. Enter a dimly-lit room.
2. Put on your safety goggles.
3. Use tape to affix the ruler to the work surface.
4. Place the flashlight adjacent to the ruler with its face at the 0 cm mark, pointed down the ruler, and secure with tape. See Figure 17.
Note: Tape the flashlight such that the on/off switch is easily accessible.
Figure 17.
Placement of flashlight on book at 0 cm mark of the ruler.
1. Fold the paper into three equal sections, as shown in Figure 18.
Figure 18.
Steps for making a tri-fold paper.
1. Place the folded paper such that it stands at the end of the ruler, near the 30 cm mark.
2. Review the safety and setup procedures provided in the packaging of the digital multimeter.
3. Attach one jumper cable to each DMM lead.
Note: The leads should connect to the VΩmA and ground ports. Do not connect to the AC port.
1. Connect the jumper cables to the photocell by attaching one jumper cable to each leg of the photocell. Refer to Figure 19.
Figure 19.
Digital multimeter connection to photocell.
1. Turn on the flashlight.
2. Tape the jumper cables so that the photocell is in a standing position, with the cell facing toward the flashlight, at the 20 cm mark of the ruler. See Figure 20.
Note: Adjust the photocell position as needed so it is in the brightest region of the light from the flashlight.
Figure 20.
Setup of photocell and flashlight. The photocell is positioned facing the flashlight (top). A closeup of the photocell in a standing position with its face pointed toward the flashlight (bottom left). The photocell as seen from the 0 cm mark of the ruler: the photocell’s shadow lies within the brightest region of the flashlight’s light path, as seen on the folded paper screen (bottom right).
1. Turn off the flashlight.
2. Turn on the DMM and select the 20 kΩ setting.
3. Record the resistance R0 reading from the DMM in Data Table 1.
Note: Depending on the darkness of the room, the resistance reading may be higher than the maximum resistance reading for the 20 kΩ setting. If this happens, change the DMM to the 200 kΩ or 2000 kΩ setting. Return to the 20 kΩ setting whenever possible to collect data with the maximum number of significant figures.
1. Calculate the background intensity 1/R0 and record in Data Table 1.
Note: The DMM should be reset to 20 kΩ if it was moved for the recording in step 13.
Part 2: One Polarizer
1. Turn on the flashlight.
Note: The flashlight will remain on for the remainder of this exercise.
1. Record the resistance value R for 0 polarizing cards in Data Table 2.
2. Calculate the intensity 1/R and record in Data Table 2.
Note: Intensity is reported in arbitrary units (a.u.).
1. Calculate the adjusted intensity 1/R – 1/R0 and record in Data Table 2.
2. Place one polarizing card in a binder clip with its polarization axis perpendicular to the clip opening. See Figure 21.
Figure 21.
Setup of polarizing card in a binder clip. The polarization axis is perpendicular to the binder clip and parallel to the table.
1. Position the binder clip with polarizing card at the 15 cm mark of the ruler, such that its polarization axis is parallel to the table, with the photocell fully visible through the card, as indicated by the shadow on the tri-fold paper. See Figure 22.
Figure 22.
Polarizing card at the 15 cm mark in correct orientation. The shadow of the photocell is centered in the shadow of the polarizing card.
1. Record the resistance value for one card R in Data Table 2.
2. Calculate the intensity 1/R for one card and record in Data Table 2.
3. Calculate the adjusted intensity for one card 1/R – 1/R0 and record in Data Table 2.
4. Calculate the ratio of the intensity with one polarizing card and the intensity with no polarizing cards:
ratio=(1R−1R0)1 card(1R−1R0)0 cardsratio=(1R−1R0)1 card(1R−1R0)0 cards
1. Record the ratio in Data Table 2.
Part 3: Two Crossed Polarizers
1. Place a second polarizing card in another binder clip with its polarization axis perpendicular to the binder clip, as described in Part 2.
2. Position the binder clip with polarizing card at the 5 cm mark of the ruler (10 cm from the card located at the 15 cm mark) with its polarization axis parallel to the table.
3. Record the resistance value R for 0° in Data Table 3.
Angle (°) Resistance R (kΩ) Relative Light Intensity 1/R (a.u.) Adjusted Light Intensity 1/R – 1/R0 (a.u.)
0
15
30
45
60
75
90
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
360
4. Remove the polarizing card placed at the 15 cm mark.
5. Rotate the polarizing card by 15°, using the protractor to measure the angle. The side of the card which is parallel to the polarization axis should align with the 15° mark of the protractor. Refer to Figure 23.
Note: Align the angle with one eye closed for best results. No part of the card should be below the base of the binder clip.
Figure 23.
Aligning the polarizing card to a 15° angle using the protractor.
1. Return the polarizing card in the binder clip set to 15° to the 15 cm mark, ensuring the card placement aligns with the photocell, as shown in Figure 24.
Note: Use the shadow on the folded paper to ensure the photocell and card align properly. The photocell shadow should be fully visible on the folded paper screen at all times. Do not let the polarizing card slip such that the angle changes.
Figure 24.
Aligning the polarizing cards so that the photocell shadow is fully visible on the paper.
1. Record the resistance value R for 15° and record in Data Table 3.
2. Determine the intensity 1/R and record in Data Table 3.
3. Determine the adjusted intensity 1/R – 1/R0 and record in Data Table 3.
4. Repeat steps 30-35 for the remaining angles in Data Table 3.
Note: Angles beyond 180° may be difficult to measure. You may want to subtract 180° from the angle being measured for ease. For example, when measuring 195°, this is equivalent to 195° – 180° = 15°. However, this angle should be measured from the opposite side of the card as was done originally – the card should make one complete rotation during this process.
1. Create a graph with angle on the x-axis and adjusted intensity on the y-axis.
2. Label the axes of the graph, including units, then title the graph and upload an image in Graph 1.
Part 4: Three Crossed Polarizers
1. Remove the polarizing card placed at the 15 cm mark.
2. Rotate the polarizing card such that its polarization axis is at the 90° position, using the protractor to measure the angle, and replace the polarizing card to the 15 cm mark.
3. Place a third polarizing card in another binder clip with its polarization axis perpendicular to the binder clip, such that its polarization axis will be parallel to the table when set down.
4. Set the binder clip with the third polarizing card at the 10 cm mark of the ruler with its polarization axis parallel to the table, ensuring the card aligns with the other cards and the photocell.
Note: The shadow of the photocell will not appear in this configuration. Align the cards by eye, looking at the filters at an angle, from the flashlight end of the configuration.
1. Record the resistance value R for 0° in Data Table 4.
2. Data Table 4: Resistance and Light Intensity for Three Crossed Polarizers
Angle (°) Resistance R (kΩ) Relative Light Intensity 1/R (a.u.) Adjusted Light Intensity 1/R – 1/R0 (a.u.)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
3. Remove the polarizing card placed at the 10 cm mark.
4. Rotate the polarizing card by 10°, using the protractor to measure the angle.
Note: The side of the card parallel to the polarization axis should align with the 10° mark of the protractor.
1. Return the polarizing card in the binder clip set to 10° to the 10 cm mark. Ensure the card placement aligns with the other polarizing cards.
2. Record the resistance value R for 10° and record in Data Table 4.
3. Determine the intensity 1/R and record in Data Table 4.
4. Determine the adjusted intensity 1/R – 1/R0 and record in Data Table 4.
5. Repeat steps 44-49 for the remaining angles in Data Table 4.
6. Turn off the flashlight.
7. Create a graph with angle on the x-axis and adjusted intensity on the y-axis.
8. Label the axes of the graph, including units, title the graph, and upload an image in Graph 2.
Cleanup:
• Return all HOL materials to the lab kit for use in future experiments.
Exercise 2 – Questions
1. Why was this exercise performed in a dimly-lit room? What was the purpose of measuring the background intensity?
2. What is the transmitted intensity of light if unpolarized light passes through a single polarizing filter and the initial intensity is 80 W/m2?
When unpolarized light passes through first polarizer, it’s intensity will be reduced to half
I1 = I0/2
Given that I0 = 80 W/m^2, So
I1 = 80/2 = 40 W/m^2
3. What is the transmitted intensity of light if an additional polarizer is added at a 60° angle to the setup described in Question 2? Show all work in your answer.
Now after passing through 1st polarizer light is polarized, So Using Malus’s law:
After that when light passes through 2nd polarizer, Intensity will be
I2 = I1*(cos A1)^2
A1 = Angle between both polarizer = 60 deg, So
I2 = 40*(cos 60 deg)^2
I2 = 10 W/m^2
4. What is the transmitted intensity of light if an additional polarizer is added perpendicular to the first polarizer in the setup described in Question 3? Show all work in your answer.
I2= (10)(cos30)^2= 7.5 w/m^2
5. How do Graphs 1 and 2 illustrate the behavior of light transmission through two and three polarizing cards?
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