Home›MPPSC Forest›State Forest Service Mains Exam›Section 'B': Forestry and General Science›UNIT-07: Physics›Light: Nature of light, reflection of light, laws of reflection, reflection from plane and curved surface, image formation by plane, convex and concave mirror, relation between focal length and radius of curvature, determination of focal length of concave mirror by single pin method, relation between u, v, f (numerical examples)›What is the focal length of a plane mirror?

What is the focal length of a plane mirror?

20192M#mppsc-forest#pyq#mcq#2019
A.0
B.10 cm
C.20 cm
D.∞Correct
Explanation & Solution

Correct Answer: (D) ∞

A plane mirror can be considered as a spherical mirror with an infinitely large radius of curvature (R=∞R = \inftyR=∞). Since focal length f=R/2f = R/2f=R/2, the focal length of a plane mirror is infinity.

हिंदी में प्रश्न एवं आदर्श उत्तर

किसी समतल दर्पण की फोकस दूरी क्या होगी ?

A.0
B.10 सेमी
C.20 सेमी
D.∞सही

सही उत्तर: (D) ∞

समतल दर्पण को अनंत वक्रता त्रिज्या वाले गोलीय दर्पण के रूप में माना जा सकता है। चूँकि फोकस दूरी f=R/2f = R/2f=R/2 होती है, इसलिए समतल दर्पण की फोकस दूरी अनंत (∞\infty∞) होती है।

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