Exampro A-level Physics (7407/7408)
Name:
PAL Prep Wk11
Class:
Author:
Chella Nathan
Date:
Time:
90
Marks:
60
Comments:
Page 1 of 9
Q1.
(a) Figure 1 shows the electron gun that accelerates electrons in an electron
microscope.
Figure 1
(i)
Draw, on Figure 1, electric field lines and lines of equipotential in the region between
the anode and cathode. Assume that there are no edge effects and that the holes in
the plates do not affect the field.
Clearly label your diagram.
(3)
(ii)
Calculate the kinetic energy, speed and momentum of an electron as it passes
through the hole in the anode.
mass of an electron
charge of an electron
=
=
9.1 × 10–31 kg
–1.6 × 10–19 C
(4)
Page 2 of 9
(b)
By calculating the de Broglie wavelength of electrons coming through the anode of this
device, state and explain whether or not they will be suitable for the investigation of the
crystal structure of a metal.
Planck constant
=
6.6 × 10–34 J s
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(4)
(Total 11 marks)
Q2.
An electron has a kinetic energy E and a de Broglie wavelength λ. The kinetic energy is
increased to 4E. What is the new de Broglie wavelength?
A
B
C
λ
D
4λ
(Total 1 mark)
Q3.
(a)
When monochromatic light is shone on a clean cadmium surface, electrons with a
range of kinetic energies up to a maximum of 3.51 × 10–20 J are released. The work
function of cadmium is 4.07 eV.
(i)
State what is meant by work function.
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(2)
Page 3 of 9
(ii)
Explain why the emitted electrons have a range of kinetic energies up to a maximum
value.
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(4)
(iii)
Calculate the frequency of the light. Give your answer to an appropriate number of
significant figures.
answer = ................................ Hz
(4)
(b)
In order to explain the photoelectric effect the wave model of electromagnetic radiation was
replaced by the photon model. Explain what must happen in order for an existing scientific
theory to be modified or replaced with a new theory.
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(2)
(Total 12 marks)
Q4.
(a)
State what is meant by the wave-particle duality of electrons.
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(1)
Page 4 of 9
(b)
Electrons of wavelength 1.2 × 10–10 m are required to investigate the spacing between
planes of atoms in a crystal.
(i)
Calculate the momentum of an electron of this wavelength stating an appropriate
unit.
momentum of electron = ................................................
(3)
(ii)
Calculate the speed of such an electron.
speed of electron = .............................................. m s–1
(2)
(iii)
Calculate the kinetic energy of such an electron.
kinetic energy of electron = .................................................... J
(2)
(Total 8 marks)
Q5.
(a)
(i)
Explain what is meant by the duality of electrons.
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(ii)
State the relation between the electron mass, electron velocity and the wavelength
for a monoenergetic beam of electrons.
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(3)
Page 5 of 9
(b)
The spacing of atoms in a crystal is 1.0 × 10–10 m.
mass of the electron
the Planck constant
=
=
9.1 × 10–31 kg
6.6 × 10–34 J s
Estimate the speed of electrons which would give detectable diffraction effects with such
crystals.
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(4)
(c)
Give one piece of evidence to demonstrate that electrons have particle properties.
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(1)
(Total 8 marks)
Q6.
(a)
(i)
Electrons behave in two distinct ways. This is referred to as the duality of electrons.
State what is meant by the duality of electrons.
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(ii)
Give one example of each type of behaviour of electrons.
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(3)
(b)
Calculate the speed of electrons that have a de Broglie wavelength of 1.70 × 10–10 m.
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(2)
(Total 5 marks)
Page 6 of 9
Q7.
(a) Calculate the de Broglie wavelength of an electron travelling at 2.00% of the speed of
light.
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(b)
Determine the frequency of the electromagnetic radiation that would have the same
wavelength as this electron.
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(Total 5 marks)
Q8.
(a)
(i)
State what is meant by the wave-particle duality of electromagnetic radiation.
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(ii)
Which aspect of the dual nature of electromagnetic radiation is demonstrated by the
photoelectric effect?
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(2)
(b)
A metal plate is illuminated with ultra violet radiation of frequency 1.67 × 1015 Hz. The
maximum kinetic energy of the liberated electrons is 3.0 × 10–19 J.
(i)
Calculate the work function of the metal.
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Page 7 of 9
(ii)
The radiation is maintained at the same frequency but the intensity is doubled. State
what changes, if any, occur to the number of electrons released per second and to
the maximum kinetic energy of these electrons.
number per second ...............................................................................
maximum kinetic energy ........................................................................
(iii)
The metal plate is replaced by another metal plate of different material. When
illuminated by radiation of the same frequency no electrons are liberated. Explain
why this happens and what can be deduced about the work function of the new
metal.
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(8)
(Total 10 marks)
Page 8 of 9
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