A light wave has plane wavefronts described by x + y + z = constant. The angle made by the direction of wave propagation with the x-axis is:
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Question

A light wave has plane wavefronts described by x + y + z = constant. The angle made by the direction of wave propagation with the x-axis is:

G1 Physics · Accepted Answer

The direction of propagation is perpendicular to the wavefront. For the plane x + y + z = constant, a normal vector is n = (1,1,1). The x-axis direction is (1,0,0). Therefore cosα = (1)/(√(1²+1²+1²)) = 1/√3. Hence α = cos⁻¹(1/√3). Correct option: A.