When an object is placed at a distance of 25cm from a mirror, the magnification is m1 and when the object is moved 15cm farther away with respect to the earlier position and the magnification becomes m2. m1/m2=4,then the focal length of the mirror is————————— and which mirror is it
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Answered by
51
We know that 1/d0 + 1/d1 = 1/f
when do1 = -25cm
-1/25+1/d11=1/f ------1
-d11/25 = m1 --------2
When do2 = -40cm
-1/40 + 1/d12 = 1/f -------3
-d12/40 = m2 --------4
2/4
=>d11/d12 = 5/2
let d1=5x and d12=2x
1-3
=>1/d11 – 1/d12 = 1/25 – 1/40 = 3/200
=>1/5x – 1/2x = 3/200
=>x=-20
d11=-100
putting it in 1
we get f=-20m.
when do1 = -25cm
-1/25+1/d11=1/f ------1
-d11/25 = m1 --------2
When do2 = -40cm
-1/40 + 1/d12 = 1/f -------3
-d12/40 = m2 --------4
2/4
=>d11/d12 = 5/2
let d1=5x and d12=2x
1-3
=>1/d11 – 1/d12 = 1/25 – 1/40 = 3/200
=>1/5x – 1/2x = 3/200
=>x=-20
d11=-100
putting it in 1
we get f=-20m.
Answered by
10
Answer:
f=-20cm where f is focal length
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