PHY4 June 2005
PHY4 June 2005
PHY4 June 2005
(b) The number of photons hitting a square metre in one second at this distance from the bulb is 2.4 x 1017.
Find the average energy of the photons in electronvolts. (3)
4. A stationary wave of amplitude 4.0cm is produced by the superposition of two progressive waves that travel in
opposite directions.
(a) Define the term amplitude. (1)
(b) The graph below shows the positions of the stationary wave and of one of the two progressive waves
at a particular instant.
Apply the principle of superposition to determine the displacement of the other progressive wave at positions A, B and
C on the distance axis at this same instant. (3)
Plot these displacement values on a copy of the graph.
Hence draw one complete wavelength of this progressive wave. (3)
PHY4 JUNE 2005 1 hour 20 minutes 2
1cm
7. (a) What is meant by the Doppler effect (electromagnetic Doppler effect) when applied to light? (2)
(b) Edwin Hubble reached a number of conclusions
as a result of observations and measurements of red-shift.
State two of these conclusions. (2)
(c) The diagram gives values of wavelength for part of
the electromagnetic spectrum. A very hot distant galaxy
emits violet light just at the edge of the visible spectrum.
Estimate the maximum velocity the galaxy could have
so that visible light could still be detected as it moves away from the Earth. (4)
(d) The fate of the Universe is dependent on the average mass-energy density of the Universe.
What is meant by the critical density of the Universe? (2)
8. The photoelectric effect supports a particle theory of light but not a wave theory of light.
Below are two features of the photoelectric effect.
For each feature explain why it supports the particle theory and not the wave theory.
(a) Feature 1: The emission of photoelectrons from a metal surface can take place instantaneously.
(b) Feature 2: Incident light with a frequency below a certain threshold frequency cannot release electrons from a metal
surface. (4)