A plano-concave lens has r₁ = 15 cm and is constructed of a material with refractive index of 1.5. The focal length of the lens is A) -15 cm B) 15 cm C) -30 cm D) 30 cm E) None of these is correct.

Question

Quizplus · Accepted Answer

The focal length of a plano-concave lens can be given by:

f = -R/(n-1)

where R is the radius of curvature of the spherical surface, n is the refractive index of the lens material, and the negative sign indicates that the lens is a diverging lens.

In this case, the lens has a flat surface and a concave surface with a radius of curvature of -15 cm (since the surface is concave). Therefore,

f = -(-15 cm)/(1.5-1) = -(-15 cm)/0.5 = 30 cm.

So the correct answer is (C): F1F1F1S1F1F1F1030 cm.

A Plano-Concave Lens Has R1 = 15 Cm and Is

A Plano-Concave Lens Has R₁ = 15 Cm and Is