Question

If the refractive indices of crown glass for red, yellow and violet colours are 1.5140. 1.5170 and 1.5318 respectively and for flint glass these are 1.6434, 1.6499 and 1.6852 respectively, then the dispersive power for crown and flint glass are respectively:

• A. 0.034 and 1.0
• B. 0.064 and 0.034
• C. 1.3 and 0.064
• D. 0.034 and 0.064

Answer 1

Step 1: Given

Refractive indices of crown glass for red, yellow and violet colours are 1.5140. 1.5170 and 1.5318 respectively.

Refractive indices of flint glass for red, yellow and violet colours are 1.6434, 1.6499 and 1.6852 respectively.

Step 2: Formula used

Dispersive power is given by

$\text{ω}=\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}$

Step 3: Calculation

For crown glass:

$\text{ω}=\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}$

$\Rightarrow \text{ω}=\frac{1.5318-1.5140}{1.5170-1}$

$\Rightarrow \text{ω}=0.034$

For flint glass

$\text{ω}=\frac{{\mu }_v-{\mu }_r}{{\mu }_y-1}$

$\Rightarrow \text{ω}=\frac{1.6852-1.6434}{1.6499-1}$

$\Rightarrow \text{ω}=0.064$

Hence, correct option is (c).