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Asked in GSEB Board July 2015 · Mirror formula and magnification
Given: concave mirror, f = -20 cm, object 25 cm in front so u = -25 cm.
Idea: find v from the mirror formula, then use m = -v/u.
1/v = 1/f-1/u = -1/(20)+1/(25) = (-5+4)/(100) = -1/(100)
v = -100 cm: the image is 100 cm in front of the mirror, where light really meets, so it is real.
m = -v/u = -(-100)/(-25) = -4
The object sits between f and 2f, so a real, inverted, enlarged image is exactly what to expect; the lateral magnification is -4.
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