AP EAPCET 24-Aug-2021 Shift 1 Paper

(c) Given, refractive index of lens, µ=1.5
Radius of curved face, R1=12‌cm
Radius of plane face, R2=∞
Now, using the expression of focal length.

1

f

=µ−1[

1

R1

−

1

R2

]
Substituting the values, we get

1

f

=(1.5−1)[

1

12

−

1

∞

]

1

f

=0.5×

1

12

⇒f=

12

0.5

‌cm=24‌cm
Hence, the focal length of given plano-convex lens is 24‌cm.