Engineering
Physics
Plane Surface Refraction
Spherical Mirror New
Question

A concave mirror has radius of curvature of 40 cm. It is at the bottom of a glass that has water filled up to 5 cm (see figure). If a small particle is floating on the surface of water, its image as seen, from directly above the glass, is at a distance d from the surface of water. The value of d is close to :

(Refractive index of water = 1.33)

8.8 cm

6.7 cm

11.7 cm

13.4 cm

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Solution

Light incident from particle P will be reflected at mirror.

u=–5cm, f=m–R2=–20cm

1v+1u=1f  ;  v1=+203cm

This image will act as object for light getting refracted at water surface.

So, object distance  d=5+203=353cm

Below water surface.

After refraction, final image is at

d'=d(μ2μ1)=(353)(14/3)

=354=8.75  cm

≈ 8.8 cm