NCERT Solutions for Class 12 Term_policy Physics Part Ii Chapter 11 Dual Nature Of Radiation And Matter

Why are infra-red waves often called heat waves? Explain.

What do you understand by the statement, 'Electromagnetic waves transport momentum'?

If light of wavelength 412.5 nm is incident on each of the metals given below, which ones will show photoelectric emission and why?

The surface of a metal is illuminated with the light of 400 nm. The kinetic energy of the ejected photoelectrons was found to be 1.68 eV. The work function of the metal is (hc = 1240 eV nm)

• 3.09 eV

• 1.41 eV

• 151 eV

• 1.68 eV

Wave property of electrons implies that they will show diffraction effects. Davisson and Germer demonstrated this by diffracting electrons from crystals. The law governing the diffraction from a crystal is obtained by requiring that electron waves reflected from the planes of atoms in a crystal interfere constructively (see in the figure).



If a strong diffraction peak is observed when electrons are incident at an angle ‘i’ from the normal to the crystal planes with distance’ between them (see figure), de Broglie wavelength λdB of electrons can be calculated by the relationship (n is an integer) 

• d sin i = nλ_dB

• 2d cos i = nλ_dB

• 2d sin i = nλ_dB

• d cos i = nλ_dB

Wave property of electrons implies that they will show diffraction effects. Davisson and Germer demonstrated this by diffracting electrons from crystals. The law governing the diffraction from a crystal is obtained by requiring that electron waves reflected from the planes of atoms in a crystal interfere constructively (see in the figure).



In an experiment, electrons are made to pass through a narrow slit of width’ comparable to their de Broglie wavelength. They are detected on a screen at a distance ‘D’ from the slit (see figure). 

Which of the following graph can be expected to represent the number of electrons ‘N’ detected as a function of the detector position ‘y’(y = 0 corresponds to the middle of the slit)? 

A photon of frequency v has a momentum associated with it. If c is the velocity of light, the momentum is

• v /c

• h v c

• h v /c²

• h v /c

The time by a photoelectron to come out after the photon strikes is approximately

• 10⁻¹ s

• 10⁻⁴ s

• 10−¹⁰ s

• 10⁻¹⁶ s

An alpha nucleus of energy 1 /2 mv² bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to 

• 1/Ze

• v²

• 1/m

• 1/v⁴

If I₀ is the intensity of the principal maximum in the single slit diffraction pattern, then what will be its intensity when the slit width is doubled?

• 2I₀

• 4I₀

• I₀

• I₀/2