## Optics B/C

Pettywap
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### Re: Optics B/C

A pair of ideal polarizing filters are placed one in front of the other near a source of light so that the rays arrive perpendicular to the planes of the filters. What angle should the polarization axes be placed so that the second filter transmits 0.25 of the light energy it receives?
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UTF-8 U+6211 U+662F
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### Re: Optics B/C

A pair of ideal polarizing filters are placed one in front of the other near a source of light so that the rays arrive perpendicular to the planes of the filters. What angle should the polarization axes be placed so that the second filter transmits 0.25 of the light energy it receives?
$\cos^2 \theta = \frac14; \cos \theta = \frac12; \theta = \frac\pi3 = 60 \degree.$

Pettywap
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### Re: Optics B/C

A pair of ideal polarizing filters are placed one in front of the other near a source of light so that the rays arrive perpendicular to the planes of the filters. What angle should the polarization axes be placed so that the second filter transmits 0.25 of the light energy it receives?
$\cos^2 \theta = \frac14; \cos \theta = \frac12; \theta = \frac\pi3 = 60 \degree.$
"Who's Fettywap?"

UTF-8 U+6211 U+662F
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### Re: Optics B/C

A converging lens in air is placed underwater. What happens to the lens?

Hint: Be careful.

chopchpp
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### Re: Optics B/C

A converging lens in air is placed underwater. What happens to the lens?

Hint: Be careful.
focal length increases?

UTF-8 U+6211 U+662F
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### Re: Optics B/C

A converging lens in air is placed underwater. What happens to the lens?

Hint: Be careful.
focal length increases?
There's more to the correct answer.

Hint 2: I didn't specify what the lens was made out of.

Pettywap
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### Re: Optics B/C

A converging lens in air is placed underwater. What happens to the lens?

Hint: Be careful.
focal length increases?
There's more to the correct answer.

Hint 2: I didn't specify what the lens was made out of.
It also depends on the index of refraction of the lens. The focal length could be infinity because the converging lens could be the same material as water, which means there is no refraction.
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### Re: Optics B/C

Almost there, a little more to the answer.

UTF-8 U+6211 U+662F
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### Re: Optics B/C

All right, my question killed the marathon, so I'll just post the answer.
If the refractive index of the lens > 1.33: The focal length increases.
If the refractive index of the lens = 1.33: The lens becomes invisible.
If the refractive index of the lens < 1.33: The lens becomes diverging.
1) Fill in the blank: Stars moving toward us appear more _ (color).
2) Why is this?

jonboyage
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### Re: Optics B/C

All right, my question killed the marathon, so I'll just post the answer.
If the refractive index of the lens > 1.33: The focal length increases.
If the refractive index of the lens = 1.33: The lens becomes invisible.
If the refractive index of the lens < 1.33: The lens becomes diverging.
1) Fill in the blank: Stars moving toward us appear more _ (color).
2) Why is this?
Blue; wavelength decreases due to Doppler shift
I was in a bin

Rustin '19
UPenn '23