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CBSE Class 10 Answered

How far from a lamp must a concave mirror of focal length 3m be placed in order to throw an image on a screen 8m from the lamp?answer is 4m.draw its ray diagram.
Asked by divjots73 | 29 Sep, 2018, 11:14: AM
answered-by-expert Expert Answer
we have mirror equation, (1/v) + (1/u) = 1/f ........................(1)
 
v = mirror-to-image distance = 8 m
u = mirror-to-object distance , f = focal length = 3 m
 
hence (1/8) +(1/u) = ( 1/3)  ...........................(2)
by solving eqn.(2), we get u = 4.8 m
Answered by Thiyagarajan K | 29 Sep, 2018, 13:11: PM

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