CUET · PHYSICS · PYQ PAPER 2025
A light ray from air is incident on a glass slab (\( \mu = 1.5 \)) as shown in the figure. It undergoes a total internal reflection and travels along AB. The thickness AC of the glass slab is 20 cm. The time taken by light to cross the glass slab after reflection is
- A 1.2 ns
- B 2 ns
- C 0.06 ns
- D 1.3 ns
Answer & Solution
Correct Answer
(B) 2 ns
Step-by-step Solution
Detailed explanation
\(\cos \left(60^{\circ}\right)=\frac{A C}{A B}\) \(A B=\frac{A C}{\cos \left(60^{\circ}\right)}=\frac{0.2}{1 / 2}=0.4 m\) \(t=\frac{A B}{v}\) \(t=\frac{0.4}{2 \times 10^8}=0.2 \times 10^{-8} s\) \(t=2 \times 10^{-9} s\) \(t=2 ns\)
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