A 5 cm long pin is placed 50 cm far from a concave mirror of focal length 40 cm. Its image will be formed at _______.

Question

Question

This question was previously asked in

RRB Group D 13 Sept 2022 Shift 2 Official Paper

Answer 1

The correct answer is 2m in front of the mirror.

Key Points

The focal length of the concave mirror can be formed by the formula:
- \(1\over f \)= \(1\over V\) + \(1\over U\)

F = focal length of the mirror, V = image distance from the pole and U= object distance from the pole

Here, the focal length is -40 cm and the object distance is - 50 cm.

\(1\over v\) = \(1\over f\) - \(1\over u\)

\(1\over v\) = - \(1\over 40\) - ( - \(1\over 50\))

\(1\over v\) = - \(1\over 40\) + \(1\over 50\)

\(1\over v\) = \(4-5\over 200\)

\(1\over v \) = -\(1\over 200\) , v =200cm (1m = 100 cm)

v = 2 m so, Its image will be formed at 2m in the front of the mirror.

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