Question

if a concave mirror has a focal lenth of 10 cm , find the two positions where an object can be placed to give , in each case , an image twice the height of the object.

pls answer systematically

Answer 1

Given f = -10 cm

magnification is twice so taking m = +2 and -2

m = -v/u

2 = -v/u

v = -2u

1/f = 1/v + 1/u

-1/10 = -1+2/2u

u = -5

Now taking magnification as -2 

m = -v/u

-2 = -v/u

v = 2u

1/f = 1/v + 1/u

-1/10 = 1+2/2u

-2u = 30

or u = -15