Question

prove that

R=2f


light chapter​

Answer 1

Answer:

Consider a ray of light AB, parallel to the principal

axis, incident on a spherical mirror at point B.

The normal to the surface at point B is CB and CP

= CB = R, is the radius of curvature.

The ray AB, after reflection from mirror will pass

through F (concave mirror) or will appear to

diverge from F (convex mirror) and obeys law of

reflection, i.e., i = r.

From the geometry of the figure, if the aperture of

the mirror is small, B lies close to P.

Therefore, BF = PF

or FC = FP = PF

or PC = PF + FC

= PF + PF

or R = 2PF

or R = 2f

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Answer 2

Explanation:

Answer:

Consider a ray of light AB, parallel to the principal

axis, incident on a spherical mirror at point B.

The normal to the surface at point B is CB and CP

= CB = R, is the radius of curvature.

The ray AB, after reflection from mirror will pass

through F (concave mirror) or will appear to

diverge from F (convex mirror) and obeys law of

reflection, i.e., i = r.

From the geometry of the figure, if the aperture of

the mirror is small, B lies close to P.

Therefore, BF = PF

or FC = FP = PF

or PC = PF + FC

= PF + PF

or R = 2PF

or R = 2f

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