Question

A 2 cm height is placed at a distance of 20cm from a concave mirror a real image is formed at 40cm from the mirror. Calculate the focal length of the mirror and the size of the image

Answer 1

u = -20 cm.   h = 2cm.   real image.  v = -40 cm. 

1/v + 1/u = 1/f
1/f = -1/20 - 1/40 = -3/40.

f = -40/3 cm.

magnification = -v/u = -40/20 = -2

Size of the image = 4 cm inverted.

Answer 2

$u = 2cm \\ h = 2cm \\ v \: = 40cm$
$we \: know \: that \:$
1 / v + 1 / v = 1/f

1 / f = 1 /20 - 1/40

f = 3/40cm

magnification = - v / u = -40/20

= -2

$size \: of \: image \: 4cm$
$the \: image \: formed \: real \: inverted$