- Light of frequency 5.5x 1014 Hz is made to strike a surface whose work function is 2.5ev. Show that photoelectric effect will not take place. H= 6.6 X 1034Js
- Photoelectrons emitted by illuminating a given metallic surface constitute a “photocurrent”. What is the effect of increasing the intensity of the illumination of the magnitude of the photocurrent?
- The diagram below shows a photocell in action
- The photocell is either evacuated or filled with an inert gas at low pressure. Give one reason for this
- What is the function of the resistor R in the circuit?
- State one reason for using a particular radiation such as ultraviolet for a given photocell.
- Explain how the set-up shown in the diagram may be used as an automatic switching device for a burglar alarm.
- A monochromatic beam of radiation is directed on a clean metal surface so as to produce photoelectrons. Give a reason why some of the ejected photoelectrons have more kinetic energy than others.
- Describe with the aid of a labelled diagram an experimental set-up for observing the photoelectric effect.
- The table shows the relationship between the wavelength of a radiation falling on a surface and the energy, k of the emitted electrons.
λ (m) × 10-7 1.0 1.5 1.0 0.5 K(J) × 10-19 10 13 20 40
- Plot a graph of energy k(Y-axis) against the frequency, f, of the incident light.
- Determine the work function of the surface used (h=6.663 x 10-34Js)
- Name a device used to convert light energy directly into electric energy.
- Electrons emitted from a metal when light of a certain frequency is shone on the metal are found to have a maximum energy of 8.0 x 10-19 J. If the work function of the metal is 3.2 x 10-19 J, determine the wavelength of the light used.
- The figure below shows ultra violet light striking a polished zinc plate placed on a negatively charged gold leaf electroscope.
Explain the following observation
- The leaf of the electroscope falls.
- When the same experiment was repeated with a positively charged electroscope, the leaf did not fall.
- The work function of a certain material is 3.2 ev. Determine the threshold frequency for the material. (1 electron volt (eV) = 1.6 x 10-19 and planks constant H= 6.62 x 10-34Js)
- State what is meant by the term accommodation as applied to the human eye. (1 mk)
- The graph in the figure below shows the variation of photoelectric current with applied voltage when a surface was illuminated with light of a certain frequency.
Use this information in the figure to answer questions a and b.
- On the same axes, sketch the graph of when light of higher intensity but same frequency is used to illuminate the surface. (1 mk)
- Explain your answer in a above . (1 mk)
- Calculate the energy of a photon of red light and ultra-violet light
(λR = 7.0 x 10-7m: λv = 4.0 x 10-7m)
- The wavelength of light from a sodium lamp is 5.9 x 10-7m. A 200W sodium vapour has an efficiency of 40%. Calculate:
- The energy of one quantum of sodium light.
- The number of quanta emitted in one second
- The threshold frequency for potassium is 5.37 x 1014 Hz. When the surface of potassium is illuminated by another radiation, photoelectrons are emitted with a speed of 7.9 x 105 m/s
- The work function for potassium
- The k.e of the photoelectrons
- The frequency of the second source
- Explain the term “work function”
- A metal has a work function of 2eV. Calculate the threshold wavelength of the metal given that e= 1.6 x 10-19C and h= 6.63 x 10-19C and Me = 9x 10-31kg.