A ray travelling along +x is reflected along +y by a smooth surface. Which unit vector can be parallel to the surface normal at the point of reflection?
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Question

A ray travelling along +x is reflected along +y by a smooth surface. Which unit vector can be parallel to the surface normal at the point of reflection?

G1 Physics · Accepted Answer

Use êᵣ=êᵢ−2(êᵢ·n̂)n̂. With êᵢ=î and êᵣ=ĵ, n̂ can be chosen along (î−ĵ)/√2 or its negative. Option A is the negative equivalent.