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Question
Two plane wavefronts of light, one incident on a thin convex lens and another on the refracting face of a thin prism. After refraction at them, the emerging wavefronts respectively become
Two plane wavefronts of light, one incident on a thin convex lens and another on the refracting face of a thin prism. After refraction at them, the emerging wavefronts respectively become
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Solution
The correct option is D spherical wavefront and plane wavefront
As the wave hits the lens it is the centre of the wave that meets the glass first and so this part of the wave is slowed down first (light waves move slower in glass than they do in air). This means that the outer portions of the wave 'catch up' so increasing the curvature to form a converging beam.
As the wave leaves the lens the outer portions move into the air first and so speed up first. This means that the outer portions move off more rapidly first and so the curvature of the wave is further increased so converging the light more strongly.
Hence, the emerging wavefront is spherical wavefront.
As the wave hits the prism, it is the lower half of the wave that meets the glass first and so, this part of the wave is slowed down first. This means that the upper part is moving fast and thus, the wavefront bends as it enters the prism and so, we get a plane wavefront which is slanted.
Hence, the emerging wavefront is plane wavefront. Therefore, the answer is OPTION C.
As the wave hits the lens it is the centre of the wave that meets the glass first and so this part of the wave is slowed down first (light waves move slower in glass than they do in air). This means that the outer portions of the wave 'catch up' so increasing the curvature to form a converging beam.
As the wave leaves the lens the outer portions move into the air first and so speed up first. This means that the outer portions move off more rapidly first and so the curvature of the wave is further increased so converging the light more strongly.
Hence, the emerging wavefront is spherical wavefront.
As the wave hits the prism, it is the lower half of the wave that meets the glass first and so, this part of the wave is slowed down first. This means that the upper part is moving fast and thus, the wavefront bends as it enters the prism and so, we get a plane wavefront which is slanted.
Hence, the emerging wavefront is plane wavefront.
Therefore, the answer is OPTION C.
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