A ray of light travelling from medium I in which speed of light is $2 \times 10^{8} m / s$ to a medium II in which speed of light is $1.5 \times 10^{8} m / s$ . Choose the correct ray diagram:

I. $u = 2 \times 10^{8} m / s$

II. $v = 1.5 \times 10^{8} m / s$

Q. The speed of light in air is 3 × 10⁸ m/s. In medium X its speed is 2 × 10⁸ m/s and in medium Y the speed of light is 2.5 × 10⁸ m/s Calculate:

(a) _air n_x
(b) _air n_Y
(c) _x n_Y

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Five identical spaceships take off from Planet X, and each passes by Planet Y at a constant speed on its way to Planet Z. A science station on Planet Y observes them passing by. At which of the following speeds spaceship would be observed to have the greatest length?

The correct option is A 6×107m/SThe observed length of spaceship traveling with speed v, whose rest length is L0 is L0√1−(vc)2.Thus length is greatest for smallest value of v.Hence the ship with speed in option A has greatest observed length.

Five identical spaceships take off from Planet $X$ , and each passes by Planet $Y$ at a constant speed on its way to Planet $Z$ . A science station on Planet $Y$ observes them passing by. At which of the following speeds spaceship would be observed to have the greatest length?

The correct option is A $6 \times 10^{7} m / S$
The observed length of spaceship traveling with speed $v$ , whose rest length is $L_{0}$ is $L_{0} \sqrt{1 - (\frac{v}{c})^{2}}$ .
Thus length is greatest for smallest value of $v$ .
Hence the ship with speed in option A has greatest observed length.