Question

The refractive indices of a glass prism for violet, yellow and red colours are 1.640, 1.600 and 1.560 respectively. The dispersive power of the material of the prism is

Answer 1

The dispersive power of the material of the prism is - 2.53 which is negative.

Explanation:

Given data:

Refractive index of violet color "μv" =  1.640

Refractive index of yellow color "μy"  = 1.6

Refractive index of red color "μr" = 1.56

ω (dispersive power) = ?

Mean refractive index = μ = (μv+μy + μr )/3

                                    = (1.640 +1.6 + 1.56)/3

                                    = 4.8 /3 = 1.6

Using formula for dispersive power ω = (μv - μy - μr)/μ-1

                                                               = ( 1.640 - 1.6 - 1.56 )/ 1.6 - 1

                                                               = (1.640 - 3.16 ) / 0.6

                                                              = - 1.52 / 0.6 = - 2.53

Thus the dispersive power of the material of the prism is - 2.53 which is negative. Negative dispersive power meas the medium have anomalous dispersion.

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Answer 2

Answer:

Explanation:

Use the equation

Nv-Nr/Ny-1

Nv = refractive index of violet

Ny that of yellow that is the average = Nv+Nr/2