Question

An object 3 cm high is placed at a distance of 8 cm from a concave mirror which produces a virtual image 4.5 cm high ...... what is the focal length of the mirror?...... what is the position of image?.... draw a ray- diagram to show the formation of image

Answer 1

Answer:

h1= 3cm, u=-8cm, h2=4.5

(i) we know that,

m=h2/h1=4.5/3=1.5

and m= -v/u=

⇒ 1.5=-v/(-8)

⇒ v= 1.5× 8=12cm

We have

1/v+1/u=1/f

⇒ 1/12 + 1/(-8) =1/f

⇒ 1/f= 1/12 - 1/8= 2-3/24= -1/24

⇒ f= -24cm

(ii) v= 12cm