Question

An object is placed on the principal axis of a concave mirror of focal length 24 cm. If the image distance is 20 cm more than the object distance, the magnification of the image is
(a) 1.2
(b) 1.5
(c)2.4. (d) 4.8​

Answer 1

Answer:

option a) 1.2

Explanation:

24/20=6/5 =1.2

Answer 2

The correct option is (b), m = 1.5

Explanation:

Given that,

Focal length of the concave mirror, f = -24 cm (it is negative for concave mirror)

Let u is the object distance and v is the image distance. According to given condition, the image distance is 20 m more than the object distance,

v = 20 + u

We can find the object distance from the mirror using mirror's formula as :

$\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}$

$\dfrac{1}{20+u}+\dfrac{1}{u}=\dfrac{1}{-24}$

u = -8 cm

Image distance becomes,

v = 20 + (-8)

v = 12 cm

The magnification of the mirror is given by :

$m=\dfrac{-v}{u}$

$m=\dfrac{-12}{-8}$

m = 1.5

So, the magnification of the image is 1.5. Hence, this is the required solution.

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Mirror's formula