Question

1.Which of the following is incorrect?

(a) Classical physics fails in explaining blackbody radiation but explains the internal energy's variation with T

(b) Classical physics fails in explaining not only blackbody radiation but also the internal energy's variation with T.

(c) Plank's radiation formula includes quantum idea. (d) Plank's radiation formula uses classical statistics.

2.The J=0 to J=1 absorption frequency for CO and reduced mass of CO are respectively 1.15x10^11Hz and 1.14x10^26 kg. What is the bond length?

3.The mean free path of free electrons in a metal at room temperature is approximately？

(a) 10^2 nm (b) 10 nm (c) 10^3 nm (d) 10^-2 nm

4.The index of refraction of glass is 1.51. What is the speed of light in the crystal?

(a) 1.51 times bigger than air

(b) 2.28 times smaller than air

(c) Doesn't change

(d) 1.51 smaller than air

Answer 1

Answer 1.a) Classical physics fails in explaining blackbody radiation but explains the internal energy's variation with T.

This is wrong because according to classical physics, there should be no limit to the energy of the light produced by the electrons vibrating at high frequencies. But experimentally, the blackbody spectrum always becomes small at the left-hand side (short wavelength, high frequency). That is variation of internal energy with temperature is not explained by classical physics .

3.The mean free path of free electrons in a metal at room temperature is approximately (b) 10 nm.

4. As we know larger is the refractive index smaller is the speed of light in that medium .