Question

26 An object is placed at 20 cm in front of a convex lens of radius of curvature 15 cm. Then the image is formed at (a) 20 cm (b)-60 cm (c) 12 cm (d) 60 cm​

Answer 1

Answer:

d. 12cm

Explanation:

Object Distance = u = 20cm

Focal Length = Radius of Curvature / 2 = f = 7.5cm

Image Distance = v

Object Distance is greater than focal length, so v is real and positive

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$

$\frac{1}{7.5} = \frac{1}{20} + \frac{1}{v}$

$\frac{1}{v} = \frac{1}{7.5} - \frac{1}{20}$

$\frac{1}{v} = \frac{20 -7.5}{150}$

$\frac{1}{v} = \frac{12.5}{150} = \frac{1}{12}$

v = 12cm