an object is kept at a distance of 60 CM from a concave mirror. For getting a magnification of 1/2,focal length of the concave mirror required is?
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u= -60cm
m = 1/2
f=?
m = -v/u
1/2 = -v/-60
v=30cm
now by using mirror formula
i.e.
1/f = 1/v + 1/u
1/f = 1/30 + (-1/60)
1/f = 1/30 - 1/60
1/f = 2-1/60
1/f = 1/60
f= 60cm
but as it is a concave mirror , we will consider f= -60cm as a concave mirror has its focal length in negative.
m = 1/2
f=?
m = -v/u
1/2 = -v/-60
v=30cm
now by using mirror formula
i.e.
1/f = 1/v + 1/u
1/f = 1/30 + (-1/60)
1/f = 1/30 - 1/60
1/f = 2-1/60
1/f = 1/60
f= 60cm
but as it is a concave mirror , we will consider f= -60cm as a concave mirror has its focal length in negative.
Rahulmehta1:
but the answer is 20 cm
anyways thanks a lot
wlcm
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