Question

Please help me to find the answers ..........................An object is placed in front of a concave mirror of focal length 20 cm . The image formed is three times the size of the object . Calculate two possible distance of the object from the mirror.​

Answer 1

◆ Answer -

(a) 80/3 cm

(b) -40/3 cm

● Explanation -

Given that, image size is 3 times object size. Thus magnification is ±3.

(a) For M = +3,

v/u = +3

v = 3u

Using mirror formula,

1/f = 1/v + 1/u

1/20 = 1/3u + 1/u

Solving this,

$\boxed{u = 80/3 cm}$

(b) For M = -3,

v/u = -3

v = -3u

Using mirror formula,

1/f = 1/v + 1/u

1/20 = 1/-3u + 1/u

Solving this,

$\boxed{u = -40/3 cm}$

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