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

Question

Quizplus · Accepted Answer

The focal length of a plano-concave lens is given by the equation:

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

where n is the refractive index of the lens material, R1 is the radius of curvature of the convex surface (which is infinite for a plano-concave lens), and R2 is the radius of curvature of the concave surface.

Since R1 is infinite, 1/R1 is zero, so the equation simplifies to:

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

Substituting the given values, we get:

1/f = (1.5-1) * (-1/15)

1/f = -0.0333

f = -30 cm

Note that the negative sign indicates that the lens is a diverging lens (i.e., it spreads out incident light). The correct answer is therefore choice C: "Focal length = -30 cm".

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

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