Define and explain : (a) a wave normal (b) a ray of light.

1.	Define and explain : (a) a wave normal (b) a ray of light.
Answer» (a) Wave normal: A wave normal at a point on a wave front is defined as a line drawn perpendicular to the wave front in the direction of propagation of the wave front. In a homogeneous isotropic medium, a wave front moves parallel to itself. Thus, at any point in the medium, the direction in which the wave front moves is always perpendicular to the wave front at that point. This direction is given by the wave normal at that point. (b) Ray of light: The direction in which light is propagated is called a ray of light. This term (ray of light) is also used to mean a narrow beam of light waves. Only in a homogeneous isotropic medium is a ray of light the same as a wave normal. For spherical wave fronts spreading out from a point source, the rays are radially divergent. The rays corresponding to a plane’ wave front form a parallel beam.

Answer»

(a) Wave normal: A wave normal at a point on a wave front is defined as a line drawn perpendicular to the wave front in the direction of propagation of the wave front.

In a homogeneous isotropic medium, a wave front moves parallel to itself. Thus, at any point in the medium, the direction in which the wave front moves is always perpendicular to the wave front at that point. This direction is given by the wave normal at that point.

(b) Ray of light: The direction in which light is propagated is called a ray of light.

This term (ray of light) is also used to mean a narrow beam of light waves. Only in a homogeneous isotropic medium is a ray of light the same as a wave normal. For spherical wave fronts spreading out from a point source, the rays are radially divergent. The rays corresponding to a plane’ wave front form a parallel beam.

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