Question

radius of curvature of two faces of double convex lens is 10 cm 15 cm and its refractive 1.50 find its focal length of a lens

Answer 1

by lens maker formulae
f=(n-1)(1/R1-1/R2)
R2 will be negative therefore the formula will become
f=(n-1)(1/R1+1/R2)

Answer 2

Since the given lens is a double convex lens;R1 will be positive whereas R2 will be negative.

R1=10cm

R2=15cm

n=1.5cm

f=??

Using the lens maker formula

1/f=(n-1)(1/R1-1/R2)

1/f=(1.5-1)[1/10+1/15]

After solving the equation u will be getting the focal length as 12cm