(a) Mirror Formula: M1M2 is a concave mirror having pole P, focus F and centre of curvature C.
An object AB is placed in front of mirror with point B on the principal axis. The image formed by mirror is A' B' . The perpendicular dropped from point of incidence D on principal axis is DN.
In ΔABC and ΔA' B'C
∠ABC = ∠A' B'C (each equal to 90°)
∠ACB = ∠A'CB' (opposite angles)
Both triangles are similar.
Now in ΔDNF and A' B'F
∠DNF = ∠A'B'F (each equal to 90°)
∠DFN = ∠A'FB' (opposite angles)
∴ Both triangles are similar
If aperture of mirror is very small, the point N will be very near to P, so FN = FP
By sign convention
Distance of object from mirror PB = -u
Distance of image from mirror PB' = - v
Focal length of mirror PF = - f
Radius of curvature of mirror PC = - R = - 2f
Substituting these values in (4), we get
The corrective lens must form the image of letters of book placed at 25cm (near point) ofhypermetropic eye.