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ICSE Class 10 Physics Question 8 of 19

Refraction of Light at Plane Surfaces — Question 12

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Question 12

When an illuminated object is held in front of a thick plane glass mirror, several images are seen, out of which the second image is the brightest. Give reason.

Answer
A ray of green light enters a liquid from air, as shown in the figure. The angle 1 is 45° and angle 2 is 30°. Find the refractive index of liquid. Show in the diagram the path of the ray after it strikes the mirror and re-enters in air. Mark in the diagram the angles wherever necessary. Redraw the diagram if plane mirror becomes normal to the refracted ray inside the liquid. State the principle used. Refraction of light at plane surfaces, Concise Physics Class 10 Solutions.

As shown in the figure, if an illuminated object is held in front of a thick plane glass mirror, and is viewed obliquely, a number of images are seen and out of these the second image is the brightest.

The reason for this is that when a ray of the light falls on the surface of the mirror from the source, a small part of light (nearly 4%) is reflected forming a faint virtual image, while a large part of light (nearly 96%) is refracted inside the glass.

Now, we can see that this ray is strongly reflected back by the silvered surface inside the glass. This ray is then partially refracted in air and this refracted ray forms another virtual image.

This image is the brightest image because it is due to the light suffering a strong first reflection at the silvered surface.