JEE Advanced 2013 · Paper 1 · Physics Q2

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PhysicsSingle correct+2Question 2 of 60

A ray of light travelling in the direction $\frac12\left(\hat i+\sqrt3\hat j\right)$ is incident on a plane mirror. After reflection, it travels along the direction $\frac12\left(\hat i-\sqrt3\hat j\right)$ . The angle of incidence is

30°

45°

60°

75°

Answer and worked solution

Official answer: A

Normal. Reflection reverses the component along the normal: $\frac12(\hat i+\sqrt3\hat j)\to\frac12(\hat i-\sqrt3\hat j)$ , so the normal is along $\hat j$ .

Angle of incidence. $\cos i=\frac{\sqrt3}2$ , so $i=30°$ .

(A)

Topics:Reflection and plane mirrors Vectors

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JEE Advanced 2013 · Paper 1, Physics question 2