Purpose: To investigate the effects of polarized light

Equipment: 3 polarizing filters (dark plastic sheets)

1 small plane (flat) mirror

Discussion: The vibrations of light waves reaching your eyes are mostly randomly oriented: they vibrate in many planes at once. In polarized light, the light waves vibrate in one plane only. Polarized light can be made by blocking all of the waves except those in one plane with polarizing filters. The filters can also be used to detect polarized light.

Procedure:

1. Position one polarizing filter between your eyes and a room light source (you can use the ceiling lights). Slowly rotate the filter 3600. Observe the intensity of the light as seen through the filter.
   1. Write out your observations:

• nothing changed
• light = normal intensity and same color as it looks without the polarizing filter

1. Arrange one filter in a fixed position in front of the light source. Slowly rotate a second filter held between your eyes and the second filter.
   1. Write out your observations and reasoning:

• @ 180° = completely blue-ish purple
• @ 360° = same intensity I observed in procedure #1
• reasoning:

1. Hold the filter at your eye in a fixed position while you slowly rotate the other filter next to the light source 3600.
   1. Write out your observations and reasoning:

• immediate observation: completely blue-ish purple
• @ 180° = same intensity I observed in procedure #1
• @ 360° = completely blue-ish purple
• reasoning:

1. Rotate both of the filters through one complete rotation in the same direction at the same time.
   1. Write out your observations and reasoning:

• At each individual of 90° rotation, the intensity of the blue-ish purple light increases and decreases at different angles
• blue → white → pink → blue-ish purple → purple
• reasoning:

1. Rotate both of the filters through one complete rotation at the same time, but in opposite directions.
   1. Write out your observations and reasoning:

• At each individual of 90° rotation, the intensity of the blue-ish purple light increases and decreases at different angles
• blue → bright white → lighter blue → dark blue-ish purple
• reasoning:

1. Repeat step 1, except arrange the light source and a mirror so that you observe only the light reflecting off the mirror surface.
   1. Write out your observations and reasoning:

• there is no change in the intensity of the light
• reasoning: mirror light isn’t polarized so the intensity of the light is not changed

1. 1. Is the light reflected off a mirror polarized? How can you tell?

• the light reflected off a mirror isn’t polarized because it is just reflected, not absorbed so the particles aren’t changed. I can tell because the light I observed through the mirror looks the exact same as the light I observed when looking directly at the ceiling light.

1. View different regions of the sky on a sunny day through a filter. Rotate the filter 3600 while viewing each region.
   1. What happens to the intensity of the light as you rotate the filter?

• The light isn’t polarized when one filter is used but the light is polarized when more than one filter is used.

1. 1. Is the light of the sky polarized?
      1. If so, where is the region of maximum polarization in relation to the position of the sun?

• The light in the sky is only polarized when more than one filters are used. The maximum area of polarization can be seen in the dirent view of the sun.

8. View a liquid crystal display (LCD) on a calculator, cell phone, or laptop screen using a filter. Rotate the filter      3600, and note any intensity changes.

1. 1. What happens to the intensity of the light as you rotate the filter?

• Intensity decreases as it is rotated 180° and returns to normal as the rotation returns to its original position.

1. 1. Is this light polarized?

• yes

Analysis:

1. Why do polarized lenses make good sunglasses?

• They lessen the intensity of the sun and make it easier for us to see in the daytime.

1. Explain why the effects seen in steps 1 to 3 occur?

• Polarization occurs when an electric field distorts the negative cloud of electrons around positive atomic nuclei in a direction opposite the field. This slight separation of charge makes one side of the atom somewhat positive and the opposite side somewhat negative.

 

1. These polarization filters aren’t perfect. How do you know?

• Since they are mass-produced, they is room for large amounts of error such as scratches on the surface and uneven edges.

1. 1. If these filters were perfect, how would you know?

• We wouldn’t be able to see any light so we would see what we perceive as true black.

 

 

Purpose:  Demonstrate resonance in a closed tube and determine the speed of sound in air.

Materials:  1000 mL graduated cylinder, minimum of 5 different tuning forks, rubber mallet, PVC pipe, thermometer, meter stick

Procedure:

1. Acquire a water filled 1000 mL graduated cylinder.
2. Place the PVC pipe in the water.
3. Strike the tuning fork on the rubber block. Do NOT strike the tuning fork on anything else, and do not strike it with too much force!  Hold the tuning fork over the end of the PVC pipe as in the picture above and move the pipe up and down until the resonating sound from the tube is at its loudest.
4. Record the length of the tube (above the water, of course) in meters.  
5. Repeat this process with the other four tuning forks of different frequencies.
6. You can extend the data table for additional trials or additional tuning forks.

Data Table:

Frequency (Hz)	Length of Tube (m)	Inner Diameter of Tube (m)	Wavelength (m)	Experimental Velocity (m/s)	Accepted Velocity (m/s)	Percentage of Error
512 Hz	0.165 m	.025 m	4(0.165 + 0.4 x 0.025) = 0.7 m	0.7 x 512 = 358 m/s	331 + 0.6 (23℃) = 345 m/s	358 -345345x 100 = 4%
384 Hz	0.225 m	.025 m	4(0.225 + 0.4 x 0.025) = 0.94 m	0.94 x 384 = 361 m/s	345 m/s	361 -345345x 100 = 5%
320 Hz	0.26 m	.025 m	4(0.26 + 0.4 x 0.025) = 1.08 m	1.08 x 320 = 346 m/s	345 m/s	346 -345345x 100 = 0.3%
480 Hz	0.175 m	.025 m	4(0.175 + 0.4 x 0.025) = 0.74 m	0.74 x 480 = 355.2 m/s	345 m/s	355.2-345345x 100 = 3%
256 Hz	0.31 cm	.025 m	4(0.31 + 0.4 x 0.025) = 1.28 m	1.28 x 256 = 328 m/s	345  m/s	328 -345345x 100 = -5%

 

Helpful Information:

• The speed of sound in air is 331.5 m/s at 0o Celsius.  It increases by 0.59 m/s for every degree Celsius the temperature increases.  Knowing the temperature, you should be able to calculate the accepted value for the speed of sound.  ***23C***

Using the v = λf, you can calculate your experimental speed of sound:

The frequency of each tuning fork is stamped on the tuning fork.

The wavelength is roughly four times the length of the tube.  For this lab, you should use the more specific equation, λ = 4(length + 0.4diameter), to determine wavelength in order to get the best data.
Show sample calculations: (shown in chart above

Questions:

1. Is your percentage of error reasonable?  Include a discussion of your sources of error in your answer.

Our percent error is reasonable because they are all under 5%. Some possible sources of error that could have affected our data errors in measuring the tube length, hearing the sound waves, and the level of noise in the space that we conducted our experiment in.

 

1. What is the accepted value for the speed of sound in miles per hour?  Kilometers per hour? Nanometers per microsecond? Show your work and include units.

type of conversion	converted accepted velocity
miles per hour	345 meters1 secondx1 mile1609.34 meters x 60 seconds1 minute x60 minutes1 hour= 772 mph
kilometers per hour	345 meters1 secondx1 kilometer1000 metersx3600 seconds1 hour =1240 km/hr
nanometers per microsecond	345 meters1 second x(1x109) nanometers1 meterx1 second(1x106) microseconds=345000 nm/µs
meters per second	345 m/s

 

1. A 3.0 m long 0.15 m diameter closed organ pipe resonates when air at 20o Celsius is blown against its opening.  What is the frequency of the note produced?  Show your work.

V=f

λ = 4(length + 0.4diameter)

 

λ = 4(3.0 m + 0.4(0.15m)) = 12.24 m

331 + 0.6(20) = 343 m/s = velocity of sound in air

343 m/s12.24 m=28.0 Hz = frequency of the note produced

 

• Reflection:
  • I really enjoyed completing this lab because it was very cool to hear and compare the different frequencies. Although it was fun, we did have trouble containing the percent error of our results to 5% or more because of how quiet the frequencies were. If I were to do this lab again, I would hit the tuning forks slightly harder on the rubber mallet so that I could possibly hear the frequencies at a higher volume.

 

• Reflection:
  • I enjoyed completing this lab because it was cool to see the pulses of waves in real-life. Although I was a bit confused at first, I got the hang of it by the end of the lab. Unfortunately, since the slinky was so long and quite to conform back to its original shape, ours ended up broken.

Instructions:

1. Use  the graphic on page 2 to construct your pulley systems
2. For each pulley system, measure all necessary variables to calculate efficiency, putting your data into an excel spreadsheet. You must show me: Fr, Dr, Fe, De, Win, Wout, and Efficiency. Multiple trials (different displacements) are required (HINT: both displacements should only be vertical!). A sample of all calculations must be shown on this document.
3. Design your own custom pulley system, make the same measurements, and calculate your efficiency.

 

Materials: 1 kg mass, spring scale,  string, pulleys, and support rod to connect pulleys to.

 

Data table:

Weight (1 kg x 9.8 N)	Effort Force	Resistance Force	Resistance Distance	Effort Distance
Pulley A	10 N	9.8 N	30 cm → 0.3 m	55 cm → 0.55 m
Pulley B	3 N	9.8 N	30 cm → 0.3 m	86 cm → 0.86 m
Pulley C	4 N	9.8 N	21 cm → 0.21 m	70 cm → 0.70 m
Pulley D	4 N	9.8 N	12 cm → 0.12 m	70 cm → 0.70 m
Pulley E (Our Creation)	2 N	9.8 N	8 cm → .08 m	45 cm → 0.45 m

 

Sample calculations:

Pulley	AMA and IMA	Efficiency
A	AMA: 9.8/10 = 0.98 N IMA: 0.55 meters/0.3 meters = 1.83 m	AMAIMAx 100 = e 0.98 N1.83 mx 100 = 54.0%
B	AMA: 9.8/3 = 3.27 N IMA: 0.86 meters/0.21 meters = 4.09 m	AMAIMAx 100 = e 3.27 N4.09 mx 100 = 79.9%
C	AMA: 9.8/4 = 2.45 N IMA: 0.7 meters/0.21 meters = 3.33 m	AMAIMAx 100 = e 2.45 N3.33 mx 100 = 73.6%
D	AMA: 9.8/4 = 2.45 N IMA: 0.7 meters/0.12 meters = 5.83 m	AMAIMAx 100 = e 2.45 N5.83 mx 100 = 42.0%
E (Custom)	AMA: 9.8/2 = 4.9 N IMA: 0.45 meters/0.08 meters = 5.63 m	AMAIMAx 100 = e 4.9 N5.63 mx 100 = 87%

 

Diagram of our custom pulley system:

Analysis:

 

• How does efficiency compare to the number of pulleys?

 

We found the generally the more pulleys we have the better the efficiency.

 

• How does the ratio of distances compare to the number of string strands supporting the load?

 

This ratio represents the IMA. The higher the IMA, the better the machine should work theoretically. Since its ideal and not actual, it is theoretical.

 

• What can be done to increase the efficiency of the system?

 

Efficiency can be increased by creating a larger AMA. The closer the AMA or actual mechanical advantage is to the IMA or ideal mechanical advantage, the more efficient the system will be.

 

• How did your custom arrangement compare to the required setups?

 

The custom arrangement created a higher efficiency but used more distance effort and did not create as much distance resistance. The custom arrangement also used more force effort but also managed to lift the same weight.

 

• Why should the displacements only be in the vertical?

 

If the displacements were horizontal we would have to worry about friction and the effect of gravity pulling it down (Meaning the full force would not be used for moving it horizontal)

 

• How would you characterize your precision?

 

Our precision was decent but the pulley friction and human error may of made our precision worse.

_____________________________________________________________________________

• Personal Reflection:
  • Although I initially enjoyed creating the pulleys and testing them with weights, it became harder for me as we added more and more pulleys. If I were to perform this lab again, I would use a stronger string and pull my knots tighter so that we could get our results faster and more efficiently.

On August 30, Will Moorman, my lab partner and I completed a vector lab in which we measured the distance between the vectors we created in school and used that information to then find the resultant vector. Although it was cool to see vector addition come alive, some of the problems that we came across were:

• making a correct measurement plan on the map of the school that would achieve the requirements for the lab before we went out to collect our data
• difficulties making our vector point in a single, definite direction (i.e. N, E, S, and W)
• making our vectors a certain size so that they would fit in our plan

If we were to do this lab again, I feel like we would have better results if we collected our data in an area with less abrupt turns and furniture. Also, we would need to add our vectors analytically if we did this lab again because we did not know that we needed to do that for this lab.

Below are pictures of the lab report that we made with our results:

This week, we did a lab in which we measured how much friction force it took to make the box w a weight in it start to move and to move at a constant velocity with an acceleration of 0 m/s^2. The box that we chose weighed 284 g (0.284 kg) and the gram weights that we chose to use are the 100 g (0.1 kg), 500 g (0.5 kg), and the 1000 g (1 kg). I really enjoyed this lab because it was very interesting to see what free-body diagrams look like in person and how the force of friction was applied to the box in the lab. One mistake that we made that would make our experiment more accurate if we were to do it again, was that we accidentally read the scale in grams. Because of that mistake, we had to pause our coefficient calculations and go back to covert grams to newtons. But, overall, I feel like we did a great job executing this lab other than that small mistake that we later fixed. Below are the tables that we recorded our collected data in:

• Below is a picture of the free-body diagrams that we drew to represent our data:

Over the past few weeks, I have realized one big thing about my personal, academic personality: I am horrible at interpreting graphs because of how much they mess with my head! I have also realized that I am good at drawing them, but not so much at differentiating between the plot and slope of a d/t, v/t, and a/t graph. In order to attempt to solve this problem of confusion, I knew that I had to go to google and find a source that could explain graphs and their trends to me in the simplest terms possible. Below is a source that I found super helpful. Although I am not quite an expert at reading graphs yet, I do feel that my skills have been improving because of this source.

↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓

https://www.miniphysics.com/reading-kinematics-graphs.html 

 

On Thursday, we did a fun lab in which we brought the idea of most of our practice problems to life. I enjoyed seeing the movement of the marble in the lab because I could visualize what the velocity and acceleration looked like when they are in action. Also, I thought it was very cool how we were able to use all kinds of kinematic and projectile equations because I was able to practice using both types. Below is a data table of the results and variables I collected and a picture of my lab notebook page for this lab.

This week, we learned to ways to add vectors: graphically and analytically. As we practiced both methods, there was one thought that I just couldn’t stop thinking about: What method is truly the easiest? There are basic principles of each method that differentiate them from each other. After practicing and analyzing the methods: I think that adding them graphically is a lot simpler and easier to use.

Graphical Method Basic Principles	Analytical Method Basic Principles
Add vectors head → tail Draw a line from the tail of the first vector → head of the last vector That line = the resultant Measure length of the vector to find its magnitude Measure the angle @ the tail of the resultant to find its direction Pythagorean Theorem ⭐	You can only add perpendicular vectors If not perpendicular = break into x and y components using SOH, CAH, TOA Add x and y separately Find the angles using the inverse trig functions⭐