(a) Explain the term photoelectric effect.
(b)
The diagram above represents a photocell with its associated electric circuit. Identify each of the physical quantities
represented by the letters A, B, C, D, E and F
(c) What factor determines the: (i) current produced by the photocell
(ii) maximum kinetic energy of the photoelectrons?
(d) State one similarity and one difference between photoemission and evaporation
(e) Name two methods by which a beam of free electrons may be produced other than photoemission
(f) State two applications of photoelectric effect.
(g) A light wavelength 5.0 x 10(^{-7}) m is incident on metal resulting in photoemission of electrons. If the work function of the metal is 3.04 x 10(^{-19})J, calculate the:
(i) frequency of the light
(ii) energy of the incident photon,
(iii) maximum kinetic energy of the photoelectrons (Speed of light = 3.00 x 108ms(^{-1}); Planck’s constant = 6.6 x 10(^{-34})Js).
Explanation
(a) When EM radiation of appropriate frequency or wavelength is incident on a metal surface, it causes electrons to be emitted from the surface. This phenomenon is called photoelectric effect. It is a surface phenomenon. Emission is instantaneous and K.E. of emitted electrons depend on frequency or wavelength of incident photons.
(b) A = Incident light or EM radiations
B = Cathode
C = Photoelectrons
D = Anode
E = Vacuum (Evacuated space)
F = Glass tube
(c)(i) Intensity of the incident radiation
(ii) Energy or frequency of the incident radiation.
(d) Similarities
(i) In both, particles are emitted
(ii) Both are surface phenomenon
(iii) Both involves energy changes
Difference
(i) Evaporation involves molecules while photoemission involves electrons.
(ii) Evaporation causes cooling while photoemission does not.
(e)(i) Thermionic emission.
(ii) Ionization of gases.
(iii) Field emission
(f) Photocells can be used.
(i) To open or close doors automatically
(ii) In automatic switching device.
(iii) In television cameras
(iv) As a burglar alarm
(v) As safety devices in paper mills and related industries
(vi) To produce sounds of varying intensities on film tracks.