Two phy problems (college level) about light ray?

Airoy

2009-12-11 4:17 pm

1)A 5.64e14 Hz EM wave propagates in carbon tetrachloride(CCl4) with a speed of 2.05e8 m/s
a)What's the path of a light ray originating in the carbon tetrachloride and incident at 80(angle) on the CCI4-air interface(boundary)?
b)What's the path of a light ray originating in the carbon tetrachloride and incident at 80(angle) on the CCI4-glass interface(boundary)if n(glass)=1.6?

2)The distance between the object and eyepiece of a refracting Astronomical telescope is 25cm.If the telescope yields a magnification of 20,what is the focal length of wath lens?

回答 (1)

[匿名]

2009-12-11 5:35 pm

✔ 最佳答案

1
a. Apply Snell's law
n1/n2 = sinθ2/sinθ1

n1 = c/v = (2.05/3)
n2 = c/c = 1
θ1 = 80

sinθ2 = sinθ1 (n1/n2)
sinθ2 = 1.44

You will have total internal reflection. It is impossible for a light ray to get out.

b.

Same as above, but n1 = 1.6
sinθ2 = .901
θ2 = 64.255

2. I'm lazy and don't have the focal stuff memorized -- and I have to go. But if someone doesn't answer this, I'll post an answer when I get back

*For some reason I thought you were dealing with a telescope, not just a telescope lens -- didn't read the question. The answer is quite easy.

1/o + 1/i = 1/f
here o= 25cm
also -i/o = M = 20

1/o - M/o = 1/f
f = o/(1-M)
f = -25cm/19 = -1.315 cm ... (ignore the minus sign, this is directional.)

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