Question

An object is places at distance of 20 cm Infront of a concave lens of focal length 10 cm find the nature and location and image

Answer 1

Given:-

Object distance(u) = -20cm

Focal length (f) = -10cm

To Find:-

Image distance(v) = ?

Solution:-

We know that,

$\frac{1}{v} + \frac{1}{u} = \frac{1}{f} \\ \frac{1}{v} + \frac{1}{( - 20)} = \frac{1}{( - 10)} \\ \frac{1}{v} = \frac{1}{( - 10)} - \frac{1}{( - 20)} \\ \frac{1}{v} = \frac{1}{( - 10)} + \frac{1}{20} \\ \frac{1}{v} = \frac{ - 1}{10} + \frac{1}{20} \\ \frac{1}{v} = \frac{2 \times ( - 1) +1 \times 1 }{20} \\ \frac{1}{v} = \frac{ -2 + 1}{20} \\ \frac{1}{v} = \frac{ - 1}{20} \\ \boxed{v = - 20cm}$

The image is real and inverted and will be formed in front of the concave mirror at a distance of 20cm.