A glass plate 0.9cm thick has a refractive index of 1.50. How long does it take for a pulse of light to pass through the plate?
[c = 3.0 x 10\(^8\) ms-1]
A
4.5 x 10-11s
B
4.5 x 10-10s
C
4 .5 x 10-12 s
D
3.0 x 10-10s
Verified Correct Answer: A.
Physical Principles & Numerical Solution
N = 1.5 = \(\frac{(speed of light in glass)}{\text{speed of light in air}}\)
\(\frac{1.5}{1}\) = \(\frac{(3.0 \times 10^8)}{\text{V}}\)
V = \(\frac{(3.0 \times 10^8)}{1.5}\)
V = 2.0 x 10\(^8\) ms\(^{-1}\)
But x = Vt
t = \(\frac{\text{x}}{\text{Vt}}\)
t = (x)/v = \( \frac{9 x 10^{-3}}{2.0 x 10^8}\)
∴ Time = 4.5 x 10\(^{-11}\)S
Source: Myschool Past Questions Archive (Record #13957)