Question

the power of lens is 7.5 diopter what is its focal length in cm ?

Answer 1

power
$= \frac{1}{focal \: \: \: \: length \: \: \: \: in \: \: \: \: m}$
$7.5 = \frac{1}{f} \\ f = \frac{1}{7.5} \\ f = 0.133m$
so now in cm
f×100
=0.133×100
=13.3

Answer 2

P= 1/f
f=1/p

=1/7.5
=0.133m
=13.3cm
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