Question

a concave lens has focal length 20cm at what distance from lens are 5 cm tall object be placed so that it form an image at 15 from the lens also collect also calculated the size of image formed

Answer 1

$20 + 5 + 15 = 4 0$

Answer 2

F = - 20cm

o = 5cm

v = - 15cm

u =?

The Lens formula is below:

1/f = 1/v – 1/u

-1/20 = - 1/15 - 1/u

1/u = 1/20 – 1/15

1/u = 3 - 4/60

1/u = - 1/60

Therefore u = 60 cm

Linear magnification m = I/O, m = v/u

I/O = v/u

I/5 = -15/-60

I = 1.25