Question

A concave mirror of curvature 40 cm,used for shaving purpose produces image of double size as that of the object. Object distance must be.......

Answer 1

Answer:

30cm only

Explanation

the image is 4 times the object.thus,

(-v/u) =4

u=(-v) /4

now using the mirror formula

also here f=(-40) (focal length of concave mirror is negative)

1/f=1/v +1/u

1/(-40)=1/v + (-4)/v

1/(-40)= (-3)/v

v=3*40=120

u= (-120/4)=(-30)

u= (-30)cm

thus the object is 30 cm away in front of mirror.....