If the critical angle for internal reflection inside a certain transparent mater

Question

If the critical angle for internal reflection inside a certain transparent material is found to be 12degree, what is the index of refraction of the material? (Air is outside the material.) 1.64 2.80 3.13 4.81 How far must the screen be placed from a thin lens, of focal length 5 inches, in order for the image to cover a 2 foot wall if an object 2 inch tall is placed 4 inches from the lens? 2 feet 1.0 times 10^1 feet 2.0 times 10^1 feet Not enough information. An object is placed 20.0 cm from a double concave lens of focal length 2.0 cm. At what distance from the lens will the image be found? Is the image real or virtual? What is the magnification of the image?

Explanation / Answer

1)1/u = sin (c)

= sin 12

= 0.2079

So, u = 4.81

D) 4.81

2)we know magnification = v/u;

here, magnification = 2*12/2 = 12;

given u = 4

so, v = 4* 12 = 48 inches = 4 foot

3) 1/f = 1/v+ 1/u

-1/2 = 1/v -1/20

1/v = 1/20 -1/2

v = -2.222 cm

so, virtual image

magnification = 2.2222/2 = 1.11111

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