Question

an object 4cm high is placed 40 cm in form of concave mirror of focal length 20cm. find the distance from the mirror at which a screen be placed to obtain a sharp image (v=-40cm)

Answer 1

Explanation:

Given:

after sign conventions:

f=-12cm

u=-6cm

h0=4cm

By mirror formula,

1/f=1/v+1/u

1/v=1/f-1/u

=1/-12 +1/6

=-1/12+1/6

=1/12

v=12cm

since object is placed between P and F , we get virtual and erect

m=-v/u

=-12/-6

=+2

also m=hi/h0

2=hi/4cm

hi=8cm

hence image is magnified , that is 8cm height.

Answer 2

Answer:

v = -40 cm that is the screen should be placed at