Question

A 10.00cm. tall light bulb is placed at a distance of 90.0cm from a concave mirror having a focal length of 21 cm . Determine the images l distance and the image size

Answer 1

Given

f = -21

u = -90

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

$\frac{1}{-21} = \frac{1}{v} +\frac{1}{-90}$

$\frac{1}{v} = - \frac{1}{21} + \frac{1}{90}$

On solving above, we get

v =, -27.4 cm. (Distance of image)

For image size, we have

m = $- \frac{v}{u} = \frac{hi}{ho}$

$- \frac{-(-27.4)}{-90} = \frac{10}{ho}$

On solving above, we get

ho = 32.8 cm. (Size of Image)