Question

A dentist uses a concave mirror of radius of curvature 3 cm and places an object at a distance of x cm from the mirror to get a magnification of +5 .Find x

Answer 1

Given ;
R = -3 cm
f =R/2= -1.5 cm

m = -v/u
5 = -v/u
5u = -v
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Using mirror formula;

1/f = (1/v)+(1/u)
(-1/1.5) = (-1/5u) + (1/u)
(-10/15) = (-1+5)/5u
-2/3 = 4/5u
-10u = 12
u = -12/10
u = -1.2
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Hence the mirror should be placed 1.2cm away from the cavity to produce 5 times magnification.