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The focal lengths of a convex lens for red, yellow and violet rays are 100 cm, 98 cm and 96 cm respectively. Find the dispersive power of the material of the lens.

The focal lengths of a convex lens for red, yellow and violet rays are 100 cm, 98 cm and 96 cm respectively. Find the dispersive power of the material of the lens.

Grade:11

2 Answers

Kevin Nash
askIITians Faculty 332 Points
9 years ago
. The focal length of a lens is given by 1/f = (μ - 1) (1/R base 1 – 1/R base 2) ⇒ (μ - 1) = 1/f * 1/(1/R base 1 – 1/R base 2) = K/f ….(1) So, μ base r – 1 = K/100 …(2) Μ base y – 1 = K/98 ….(3) And μ base v – 1 = K/98 (4) So, Dispersive power = ω = μ base v - μ base r/ μ base y – 1 = (μ base v - 1) – (μ base r - 1)/( μ base y - 1) = K/96 – K/100/K/98 = 98 * 4/9600 = 0.0408
Jitender Pal
askIITians Faculty 365 Points
9 years ago
Sol. The focal length of a lens is given by 1/f = (μ - 1) (1/R base 1 – 1/R base 2) ⇒ (μ - 1) = 1/f * 1/(1/R base 1 – 1/R base 2) = K/f ….(1) So, μ base r – 1 = K/100 …(2) Μ base y – 1 = K/98 ….(3) And μ base v – 1 = K/98 (4) So, Dispersive power = ω = μ base v - μ base r/ μ base y – 1 = (μ base v - 1) – (μ base r - 1)/( μ base y - 1) = K/96 – K/100/K/98 = 98 * 4/9600 = 0.0408

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