Question

A mirror forms a real image twice the size of the object when placed 8cm in front of the mirror . find F of the mirror and its type .

Answer 1

a concave mirror bru

In the given problem,

magnifiction ,m= - 2 (since the image is inverted m is negative).

m=hiho=−2 where 'hi' and 'ho' are heights of the image and the object, respectively.

m=−vu

∴M=vu=2

v=2u

focal length of a concave mirror =- 8 cm.

(using sign convention)

Form mirror formula,

1f=1u+1v

1−8=1u+12u

−8=2u3

2u=3×(−8)

u=3×−82=3×(−4)=−12 cm

The object is placed at a distance of 12 cm from the pole of the concave mirror .

Image distance v = 2u

v=2×(−12)

v=−24 cm .

The image is formed at a distance of 24 cm from the ple, and is formed on the same side of the mirror where the object is kept.

Answer 2

Explanation:

m=-2

u=-8

m=-v/u

-v/u=-2

v/u=2

v=2u

mirror formula,

1/v+1/u=1/f

1/2u+1/u=1/f

1+2/2u=1/f

3/2u=1/f

2u/3=f

f=2*-8/3

f=-16/3

f=-5.33

this is a concave mirror