Question

Assertion: Intensity of scattered light varies inversely as the fourth power of the wavelength of incident light.

Reason: \[\lambda_{\mathrm{r}}: \lambda_{\mathrm{b}}\] is almost 2 : 1. Hence, blue is more prominent than red and the sky appears blue.

Options

• If both Assertion and Reason are true and the Reason is correct explanation of the Assertion.

• If both Assertion and Reason are true, but Reason is not correct explanation of the Assertion.

• If Assertion is true, but the Reason is false.

• If Assertion is false, but the Reason is true.

Answer 1

If both Assertion and Reason are true and the Reason is correct explanation of the Assertion. 

Explanation: 

By Rayleigh’s scattering law, $$I_s \propto \frac{1}{\lambda^4}$$. Since $$\lambda_r \approx 2\lambda_b$$, blue light is scattered about $$2^4 = 16$$ times more strongly than red light, explaining why the clear sky appears blue.