Chapter 11: Dual Nature of Radiation and Matter
Important Questions
1. The given graph shows the variation of photoelectric current (I) versus applied voltage (V) for two different photosensitive materials and for two different intensities of the incident radiations. Identify the pairs of curves that correspond to different materials but same intensity of incident radiation.
2. Draw graphs showing variation of photoelectric current with applied voltage for two incident radiations of equal frequency and different intensities. Mark the graph for the radiation of higher intensity.
3. A 12.5 eV electron beam is used to excite a gaseous hydrogen atom at room temperature. Determine the wavelengths and the corresponding series of the lines emitted.
4. An electron and a photon each have a wavelength 1.00 nm. Find
(a) their momenta,
(b) the energy of the photon and
(c) the kinetic energy
5. (a) What is the significance of negative sign in the expression for the energy?
(b) Draw the energy level diagram showing how the line spectra corresponding to Paschen series occur due to transition between energy levels.
Sample Questions
1. Write Einstein’s photoelectric equation and mention which important features in photoelectric effect can be explained with the help of this equation.
The maximum kinetic energy of the photo electrons gets doubled when the wavelength of light incident on the surface changes from λ1 to λ2. Derive the expressions for the threshold wavelength λ0 and work function for the metal surface.
2. (i) State Bohr’s quantization condition for defining stationary orbits. How does de-Broglie hypothesis explain the stationary orbits?
(ii) Find the relation between the three wavelengths from the energy level diagram shown below.
3. Write three characteristic features in photoelectric effect which cannot be explained on the basis of wave theory of light, but can be explained only using Einstein’s equation.
4. Using photon picture of light, show how Einstein’s photoelectric equation can be established. Write two features of photoelectric effect which cannot be explained by wave theory.
5. A proton and an α-particle have the same de Broglie wavelength. Determine the ratio of (i) their accelerating potentials (ii) their speeds.