Mirrors, Polaroid Films, Light/Wavelength help needed

In summary, The conversation discusses a student's confusion with a physics assignment and their calculations for a question involving polarized light and a concave mirror. The student initially chose incorrect answers but after further discussion, they determined the correct answer. The conversation also includes a discussion on drawing ray diagrams and the correct way to calculate magnification.
  • #1
riseofphoenix
295
2
:(:(:( Please ease my aching soul by helping me with this...
I submitted this assignment online and I don't know the answers yet or however many I got wrong.

Number2-2_zps32ccd6b8.png


I chose 45 because I know unpolarized light becomes this after going through a polarizer:
LCfig1.jpg


That single line is 180º, so I did 0.25 x 180º = 45º.
Is E the right answer?

Number3-4_zps647d385c.png



I chose E…but after seeing this diagram below just now, I think I got the answer wrong and that it's supposed to be B… Is E not the answer?

2fa55e0b-7598-4903-95f6-b3406b83c9d5.gif


Number5-1_zpsce573a17.png


I chose D…but I don't think it's right…
I did this:

Given:
R = 10 cm
f = -R/2 (since it's convex) = -10/2 = -5
do = ?
M = +4 x (image is upright)
di = -? (image is virtual)

M = -di/do
4 = -di/do
di = -4do

1/f = 1/do + 1/di
1/(-5) = 1/do + 1/(-4do)
-0.2 = 1/do - 1/4do
-0.2 = (4/4)1/do - (1/1)1/4do
-0.2 = (4 - 1)/4do
-0.2 = 3/4do
4do = 3/(-0.2)
4do = -0.6
do = -0.6/4
do = -0.15

Is the answer C? (I chose D originally and I can't change my answer….but now that I've worked it out step by step i think the answer is C)
 
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  • #2
riseofphoenix said:
That single line is 180º, so I did 0.25 x 180º = 45º.
Is E the right answer?
It is not, and there is no reason to multiply 180° by anything. Using the same argument, 90° would let 50% pass through, which is obviously wrong.

You can analyze this with polarization vectors and projetions on the polarization axis, or with existing formulas (Wikipedia, book, ...).

I did this:
Your result is very small (0.15 cm), there has to be some error in the calculation. I found one here:
4do = 3/(-0.2)
4do = -0.6
 
  • #3
mfb said:
It is not, and there is no reason to multiply 180° by anything. Using the same argument, 90° would let 50% pass through, which is obviously wrong.

You can analyze this with polarization vectors and projetions on the polarization axis, or with existing formulas (Wikipedia, book, ...).


Your result is very small (0.15 cm), there has to be some error in the calculation. I found one here:

So basically all three of them are wrong?
 
  • #4
mfb said:
It is not, and there is no reason to multiply 180° by anything. Using the same argument, 90° would let 50% pass through, which is obviously wrong.

You can analyze this with polarization vectors and projetions on the polarization axis, or with existing formulas (Wikipedia, book, ...).


Your result is very small (0.15 cm), there has to be some error in the calculation. I found one here:

Also, what about question number 3?
 
  • #5
:( :(
 
  • #6
riseofphoenix said:
Also, what about question number 3?
Take a spoon and test it.
The graph below is not a concave mirror.
 
  • #7
mfb said:
Take a spoon and test it.
The graph below is not a concave mirror.

Ok but my answer is still wrong though...
The answer for 3 would have to be D.
 
  • #8
Did you take the right ("inner") side of the spoon?
 
  • #9
riseofphoenix said:
Also, what about question number 3?

Think about which side of the concave surface the image lies in.

If it lies on the left (the same side as where the object resides), it is real. If on the right, then the image is virtual. The focal equation is based on the reference of the surface of the mirror. Positive distance means real and negative distance means virtual.
 
  • #10
mfb said:
Did you take the right ("inner") side of the spoon?

What do you mean?
 
  • #11
I don't know what is unclear about that question.
Like this, but with an object closer to the mirror.
 
  • #12
mfb said:
I don't know what is unclear about that question.
Like this, but with an object closer to the mirror.

So the answer IS E.
real (image on front), enlarged, inverted.
 
  • #13
riseofphoenix said:
So the answer IS E.
real (image on front), enlarged, inverted.

Not for an object lying inside of the focal point.

Why don't you try drawing out a a simple ray diagram?
 
  • #14
I did not find an image of an object closer to the focal point. The inversion is not there in your problem.
 
  • #15
TerraForce469 said:
Not for an object lying inside of the focal point.

Why don't you try drawing out a a simple ray diagram?

I forgot how to because I did this back in high school and my teacher (in college) just gave us a simple chart to follow and didn't emphasize the fact that we had to draw a ray diagram. :(
 
Last edited:
  • #16
mfb said:
I did not find an image of an object closer to the focal point. The inversion is not there in your problem.

The answer has to be B then...

Ok well since I know I got those top 3 questions wrong...I wouldn't mind moving on to the other questions I wouldn't mind you guys checking for me...

Number5-1_zpsce573a17.png


I chose D…but I don't think it's right…
I did this:

Given:
R = 10 cm
f = -R/2 (since it's convex) = -10/2 = -5
do = ?
M = +4 x (image is upright)
di = -? (image is virtual)

____________________________

M = -di/do
4 = -di/do
di = -4do

____________________________

1/f = 1/do + 1/di
1/(-5) = 1/do + 1/(-4do)
-0.2 = 1/do - 1/4do
-0.2 = (4/4)1/do - (1/1)1/4do
-0.2 = (4 - 1)/4do
-0.2 = 3/4do
4do = 3/(-0.2)
4do = -0.6
do = -0.6/4
do = -0.15

Is the answer C? (I chose D originally and I can't change my answer….but now that I've worked it out step by step i think the answer is C)
 
  • #17
riseofphoenix said:
The answer has to be B then...

Ok well since I know I got those top 3 questions wrong...I wouldn't mind moving on to the other questions I wouldn't mind you guys checking for me...

Number5-1_zpsce573a17.png


I chose D…but I don't think it's right…
I did this:

Given:
R = 10 cm
f = -R/2 (since it's convex) = -10/2 = -5
do = ?
M = +4 x (image is upright)
di = -? (image is virtual)

____________________________

M = -di/do
4 = -di/do
di = -4do

____________________________

1/f = 1/do + 1/di
1/(-5) = 1/do + 1/(-4do)
-0.2 = 1/do - 1/4do
-0.2 = (4/4)1/do - (1/1)1/4do
-0.2 = (4 - 1)/4do
-0.2 = 3/4do
4do = 3/(-0.2)
4do = -0.6
do = -0.6/4
do = -0.15

Is the answer C? (I chose D originally and I can't change my answer….but now that I've worked it out step by step i think the answer is C)

Your magnification is wrong. It's 4x smaller, which means ##\frac{d_i}{d_o}## should be less than one since ##\frac{h_i}{h_o}## is reduced.
 
  • #18
TerraForce469 said:
Your magnification is wrong. It's 4x smaller, which means ##\frac{d_i}{d_o}## should be less than one since ##\frac{h_i}{h_o}## is reduced.

Oh goodness...
So what should M equal?
 
  • #19
riseofphoenix said:
Oh goodness...
So what should M equal?

Well, it's 4x smaller so what do you think?

I'm sure you can figure this out. Other than that there seems to be nothing else wrong with your calculations.
 
  • #20
TerraForce469 said:
Other than that there seems to be nothing else wrong with your calculations.
Well, there is a calculation error in the first post, I mentioned it in post 2:
mfb said:
Your result is very small (0.15 cm), there has to be some error in the calculation. I found one here:
4d0 = 3/(-0.2)
4d0 = -0.6
 

FAQ: Mirrors, Polaroid Films, Light/Wavelength help needed

What is the difference between a regular mirror and a polarized mirror?

A regular mirror reflects all light rays equally, while a polarized mirror only reflects light rays that are vibrating in a specific direction. This results in a clearer and less distorted reflection.

How does a polaroid film work?

A polaroid film is made of long chains of molecules that are aligned in a specific direction. When light passes through the film, only light waves that vibrate in the same direction as the molecules can pass through, while other waves are absorbed. This results in a polarized light.

What is the relationship between light and wavelength?

Light is a type of electromagnetic radiation that travels in waves. The wavelength of light is the distance between two consecutive peaks or troughs of the wave. Different wavelengths of light correspond to different colors in the visible spectrum.

How is light affected by different materials?

When light passes through materials, it can be absorbed, transmitted, or reflected. The properties of the material, such as its density and chemical composition, determine how it will interact with light. This is why different objects appear different colors when exposed to light.

How can light and wavelength be manipulated?

Light and wavelength can be manipulated through various processes, such as refraction, diffraction, and interference. These processes involve changing the direction or intensity of light waves, resulting in different effects such as color separation and bending of light.

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