Examination questions on photoelectric effect involves key concepts like work function, threshold frequency, and the relationship between light frequency, photon energy, and electron kinetic energy. The photoelectric effect involves the emission of electrons from a metal surface when light shines on it. Here are some example exam questions:
Examination questions on photoelectric effect
1. (a) What is meant by threshold wavelength? (1 mark)
(b) How does intensity of radiation incident on a metal surface affect the photoelectrons emitted.
(1 mark)
(c) In an experiment using a photocell, light of varying frequency but constant intensity was made
to strike a metal surface. The maximum kinetic energy of the photoelectrons for each frequency, f,
was measured. The values obtained are shown in table 2 below
| Maximum K.E (x 10-19) | 2.8 | 5.4 | 7.4 | 9.0 | 10.0 | 11.0 |
| Frequency (x 1015) Hz | 1.5 | 1.9 | 2.2 | 2.42 | 2.57 | 2.75 |
(i) Plot a graph of maximum K.E against frequency. (5 marks)
2. The fig. below shows a photo – cell.
What factor determine the kinetic energy of the electrons emitted, hence show the relationship. (2 marks)
3. (a) What is meant by the term photo – electric effect. (1 mark)
b) The figure below shows an arrangement used to investigate photo-electric effect.
(i) Name the parts marked P and Q. (2 marks)
(ii) State three measurable quantities in this set up. (3 marks)
(iii) State how the intensity of light affects the photo – current. (1 mark)
c) The results obtained for various monochromatic radiations of different colors are shown in the grid below.
(i) The graph indicates that there is a frequency below which no electrons are
emitted. explain why this is so. (1 mark)
(ii) From the graph determine;
(i) Plank’s constant, h (Take electron charge, e = 1.6 x 10-19C) (4 marks)
Exam Questions on work functions in photoelectric effect
(ii) The work function of the metal. (3 marks)
(iii) Sketch on the same graph, the expected graph of another metal which has a lower work function than the metal used. (1 mark)
4. The graph in Figure shows the variation of frequency of radiation f with the greatest kinetic energy of the emitted electrons.
From the graph determine
(i) Plank’s constant (4mks)
(ii) Hence or otherwise calculate the work function of the metal. (3mks)
5. (a) What do you understand by the term photoelectric effect? (1mk)
(b) Name one factor that determines the velocity of photoelectrons produced
on a metal surface when light shine on it. (1mk)
(c) In a photoelectric effect experiment, a certain surface was illuminated with
radiations of different wavelengths and the stopping potential determined
for each wavelength. The table in figure 9 below shows the results obtained.
| Stopping potential (Vs) V | 1.35 | 1.15 | 0.93 | 0.62 | 0.36 |
| Wavelength (x 10-7m) | 3.37 | 4.04 | 4.36 | 2.42 | 5.46 |
On the grid provided plot a graph of stopping potential (Y-axis) against frequency. (7mks)
6. The table below shows the kinetic energy of photoelectrons for various radiations for a given photo emissive surface.
| kinetic energy (x 10-19) | 0.42 | 1.47 | 2.10 | 2.73 | 3.36 | 3.78 |
| Frequency x 1014 Hz | 4.50 | 6.00 | 7.00 | 8.00 | 9.00 | 9.75 |
i) Plot a graph of kinetic energy (y axis) against the frequency (x – axis) (5mks)
ii) Use the graph to find h the Planck’s constant (2mks)
iii) From the graph determine the work function of the surface (2mks)
iv) State 3 factors that affect the photoelectric effect (3mks)
(v) State two applications of photoelectric effect (2 marks)
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