A. 4.5 x 10-11s
B. 4.5 x 10-10s
C. 4 .5 x 10-12s
D. 3.0 x 10-10s

Correct Answer:

Option C = 4 .5 x 10-12s

Explanation

N = 1.5 = (speed of light in glass)/speed of light in air
(1.5)/1 = (3.0 x 108)/V
V = (3.0 x 108)/1.5
V = 2.0 x 108 ms-1
But x = Vt
t = (x)/Vt
t = (x)/v = (9 x 10)4/2.0x 108 = 4.5 x 10-2S
∴ Time = 4.5 x 10-12S

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