A plano convex lens of refractive index μ 1 and focal length ƒ1 is kept in contact with another plano concave lens of refractive index μ 2 and focal length ƒ2. If the radius of curvature of their spherical faces is R each and ƒ1 = 2ƒ2, then μ 1 and μ 2 are related as - (a) 3μ₂ - 2μ₁ = 1 (b) μ₁ + μ₂ = 3 (c) 2μ₁ - μ₂ = 1 (d) 2μ₂ - μ₁ = 1

Answer: (c). Plano lenses: 1/f₁ = (μ₁ - 1)/(R), 1/f₂ = (μ₂ - 1)/(R) (magnitudes). f₁ = 2f₂ ⇒ (R)/(μ₁ - 1) = (2R)/(μ₂ - 1) μ₂ - 1 = 2μ₁ - 2 ⇒ 2μ₁ - μ₂ = 1 So the answer is (c).

A plano convex lens of refractive index μ 1 and focal length ƒ1 is… | JEE Main 2019 (10 Jan, Shift 1)

Q54JEE Main 2019 · 10 JAN · SHIFT 1Medium

Combination of Lenses

A plano convex lens of refractive index $\mu$ 1 and focal length ƒ1 is kept in contact with another plano concave lens of refractive index $\mu$ 2 and focal length ƒ2. If the radius of curvature of their spherical faces is R each and ƒ1 = 2ƒ2, then $\mu$ 1 and $\mu$ 2 are related as -

Show answer and solution

Answer: (c)

Plano lenses: $\frac{1}{f_1} = \frac{\mu_1 - 1}{R}$ , $\frac{1}{f_2} = \frac{\mu_2 - 1}{R}$ (magnitudes).
$f_1 = 2f_2 \Rightarrow \frac{R}{\mu_1 - 1} = \frac{2R}{\mu_2 - 1}$
$\mu_2 - 1 = 2\mu_1 - 2 \Rightarrow 2\mu_1 - \mu_2 = 1$
So the answer is (c).

Report a mistake

Combination of Lenses question from JEE Main 2019 (10 Jan, Shift 1)

More questions on Combination of Lenses