Question

what is f if you have an object 2.0m from thw concave mirror and the image is 4.0m from the mirror
a)2.0m
b)0.67m
c)1.3m
d)4.0m

Answer 1

1/f= 1/v+ 1/u
v=4. u =2.

f=4/3m or 1.34m

Answer 2

Answer:

The focal length is 1.3m.

Explanation:

Given,

Object distance (u) = 2m

Image distance (v) = 4m

Since object and image are on the left hand, therefore by rules,

u= -2m

v= -4m

By mirror equation,

$\frac{1}{u} + \frac{1}{v} = \frac{1}{f}$

$= [-\frac{1}{2}] + [-\frac{1}{4}] = \frac{1}{f}$

$= - [ \frac{2+1}{4} ] = \frac{1}{f}$

$=- \frac{3}{4} = \frac{1}{f}$

$= -\frac{4}{3} = f$

$= 1.3 = f$

Therefore, the focal length of the concave mirror is -1.3m

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