The incident ray, reflected ray and the outward drawn normal are denoted by the unit vectors a, b, and c respectively. Then choose the correct relation for these vectors. (a) b = a + 2 c (b) b = a - 2 ( a · c) c (c) b = 2 a + c (d) b = a - c

Answer: (b). On reflection, the component of a along the normal c reverses; the component along the mirror is unchanged. Normal component = ( a · c) c, so b = a - 2( a · c) c So the answer is (b).

The incident ray, reflected ray and the outward drawn normal are… | JEE Main 2021 (26 Feb, Shift 2)

Q32JEE Main 2021 · 26 FEB · SHIFT 2Medium

Reflection & Mirrors

The incident ray, reflected ray and the outward drawn normal are denoted by the unit vectors $\vec{a},\ \vec{b}$ , and $\vec{c}$ respectively. Then choose the correct relation for these vectors.

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Answer: (b)

On reflection, the component of $\vec a$ along the normal $\vec c$ reverses; the component along the mirror is unchanged.
Normal component $= (\vec a \cdot \vec c)\vec c$ , so $\vec b = \vec a - 2(\vec a \cdot \vec c)\vec c$
So the answer is (b).

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Reflection & Mirrors question from JEE Main 2021 (26 Feb, Shift 2)

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