Question

Identify the Lens Maker’s Formula.

(a) f=(μ-1)\( ( \frac {1}{R_1} – \frac {1}{R_2} ) \)

(b) \(\frac {1}{f}\)=(μ-1)\( ( \frac {1}{R_1} – \frac {1}{R_2} ) \)

(c) \(\frac {1}{f}\)=(μ+1)\( ( \frac {1}{R_1} – \frac {1}{R_2} ) \)

(d) \(\frac {1}{f}\)=(μ-1)\( ( \frac {1}{R_1} + \frac {1}{R_2} ) \)

The question was posed to me in an interview.

This is a very interesting question from Ray Optics in portion Ray Optics and Optical Instruments of Physics – Class 12

Answer 1

The correct choice is (b) \(\frac {1}{f}\)=(μ-1)\( ( \frac {1}{R_1} – \frac {1}{R_2} ) \)

The explanation is: The lens maker formula may be defined as the formula which gives the relationship for calculating the focal length in terms of the radii of the two curvatures of the lens. It is given as:

 \(\frac {1}{f}\)=(μ-1)\( ( \frac {1}{R_1} – \frac {1}{R_2} ) \)

Where R1 and R2 are radii of curvature of the two surfaces of the lens and μ is the refractive index of the material of the lens w.r.t. medium in which the lens is placed.