Question

an object is placed at 30 cm on the principal axis of the convex lens from the lens and images formed at 60 cm from the lens find focal length​

Answer 1

Given :

▪ Distance of object = 30cm

▪ Distance of image = 60cm

▪ Type of lens : convex

To Find :

▪ Focal length of lens.

Concept :

↗ X-coordinate of centre of curvature and focus of concave lens are negative and those for convex lens are positive. In case of lenses since light rays don't reflect back in X-direction, therefore -ve sign of v indicates virtual image and +ve sign of v indicates real image.

Solution :

☞ 1/v - 1/u = 1/f

☞ 1/60 - 1/(-30) = 1/f

☞ 1/60 + 1/30 = 1/f

☞ (1+2)/60 = 1/f

☞ 3/60 = 1/f

☞ f = 60/3

☞ f = 20cm

Answer 2

Answer:

YOUR QUESTION :

an object is placed at 30 cm on the principal axis of the convex lens from the lens and images formed at 60 cm from the lens find focal length

SOLUTION :

Given :

• Distance of object : 30 cm
• Distance of image : 60 cm
• Type of lens : convex

To find :

• Focal lengths of lens

Calculation :

1/v - 1/u = 1/f

=> 1/60 - 1/(-30) = 1/f

=> 1/60 + 1/30 = 1/f

=> (1+2)/60 = 1/f

=> 3/60 = 1/f

=> f = 60/3

=> f = 20 ( Answer )