Question

how far must an object be placed in front of a convex mirror of focal length 20cm to form an image One by fourth of the size of the object​

Answer 1

Answer:

100 cm

Explanation:

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Answer 2

Answer:

The object must be placed 60 cm in front of the mirror.

Explanation:

We will use the following formula to solve this question.

$m=\frac{f}{f-u}$         (1)

Where,

m=magnification of the mirror

f=focal length of the mirror

u=object distance from the mirror

From the question we have,

f=-20cm    (The focal length of the convex mirror is negative)

m=$\frac{1}{4}$

By substituting the value of m and f in equation (1) we get;

$\frac{1}{4}=\frac{-20}{-20-u}$

$-20-u=-80$

$20+u=80$

$u=-60cm$

Hence, the object must be placed 60 cm in front of the mirror.