Question

✔ ♻♻❗❗how far from a lamp must a concave mirror of focal length 3.0 m be placed in order to throw its image on the screen 8.0 m from the lamp?❗❗❔❔❔❔

Answer 1

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Answer 2

We know, The mirror equation,

$\frac {1}{v} + \frac {1}{u} =\frac {1}{f}$ ........................(1)

Here the mirror taken is a concave mirror.

Here:  

v = mirror to image distance = 8 m

u = mirror to object distance = unknown

f = focal length = 3 m

 

Plug the values in the equation:

$\frac {1}{8} + \frac {1}{u} =\frac {1}{3}$ ...........................(2)

(or) $\frac {u+8} {8u} = \frac {1}{3}$

(or) 3u + 24 = 8u  

(or) 5u = 24

Hence, u = 4.8 m