Question

Two thin similar convex glass pieces are joined together front to front with its rear portion silvered such that a sharp image is formed 20 cm from the mirror when the air between the glass pieces is replaced by water (refractive index = 4/3) then the image formed from the mirror is at a distance of ?
1)8 cm
2)10 cm
3)6 cm
4)12 cm

Answer 1

this is convex mirror. convex mirror is in negative first you have to convert all in the minus(-) then mirror formula

Answer 2

Answer:

4) 12 cm

Explanation:

When we introduce air between glass pieces it behaves like convex mirror.

1/v + 1/u = 2/R

1/10 + 1/10 = 2/R

R = 20 cm

When water is placed between glass pieces it behave like concave mirror,

1/F = 2 x 2 (μ - 1) / R + 2/ R

Substitution of R-= 20 and μ = 4/3 we get

1/F = 1/6

Now, 1/v + 1/u = 1/F

Therefore, 2/u = 1/F = 1/6

u = 12 cms