Question

find the power of a convex lens of focal length 2.5 CM

Answer 1

ower of lens=1/f=2.5D

f=focal length in metre

2.5=1/f

Hence

f=1/2.5

f=0.4m

Hence focal length is 0.4metre (40cm)

Answer 2

Hey

focal length = 2.5 cm
focal length = 2.5/100 m
focal length = 0.025m

now 
power = 1/f(in m)
power = 1/0.025
power = +40 D

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