M
ULTIPLEC
HOICEQ
UESTIONSChoose the letter A, B, C or D that corresponds to the best answer.
31 Which of the following properties of cathode rays is incorrect? Cathode rays:
(A) come from the cathode of a discharge tube (B) have a q/m ratio less than that of the
hydrogen ion
(C) cause glass to fluoresce (D) carry energy and momentum.
32 J. J. Thomson succeeded in discovering the size of a cathode rays:
(A) charge (B) mass
(C) charge to mass ratio (D) radius.
Questions 3 and 4 refer to the following information:
Some metals will emit electrons when bombarded with high frequency light.
33 If the frequency of the light is increased without increasing the intensity:
(A) more electrons will be emitted with unchanged speed
(B) the same number of electrons will be emitted with increased speed (C) more electrons will be emitted with
increased speed
(D) the same number of electrons will be emitted with unchanged speed
34 If the intensity is increased without increasing the frequency:
(A) more electrons will be emitted with unchanged speed
(B) the same number of electrons will be emitted with increased speed (C) more electrons will be emitted with
increased speed
(D) the same number of electrons will be emitted with unchanged speed 35 p-type semiconductors:
(A) have electrons as the majority charge-carriers
(B) have holes as the majority charge-carriers (C) contain Group V donor atoms
(D) are better conductors than n-type semiconductors.
36 Silicon is preferred over germanium for semiconductor devices because:
(A) silicon is more abundant and hence is cheaper
(B) silicon has a higher ‘leakage current’ than germanium
(C) silicon is more difficult to dope than germanium
(D) silicon is harder than germanium.
37 Conduction in semiconductors is by:
(A) electrons only
(B) holes only
(C) electrons and holes
(D) depends on whether it is p-type or n-type.
38 Doping:
(A) increases the resistance of semiconductors (B) decreases the resistance of
semiconductors
(C) decreases the number of charge carriers (D) is called intrinsic semi-conduction 39 The resistance of a metal results from:
(A) collision of electrons with other electrons only
(B) collision of holes with other holes only (C) collision of electrons with imperfections in
the crystal lattice
(D) collision of holes with imperfections in the crystal lattice.
40 Bragg diffraction:
(A) proved the particle nature of X-rays (B) proved the wave nature of X-rays (C) proved the regular structure of a crystal
lattice
(D) both B and C above.
41 The correct statement is:
(A) in insulators, the valence band and conduction band overlap
(B) in conductors the valence band and conduction band overlap
(C) in semiconductors, the forbidden energy gap is larger than for insulators
(D) in conductors, the valence band is empty.
42 Superconductors:
(A) have zero resistance near 0 K (B) have zero resistance near 00C.
(C) attract magnetic fields.
(D) have resistance between that of conductors and insulators.
43 Graphs of resistance versus temperature for three materials X, Y and Z are shown in Figure 3.41. X, Y and Z are respectively:
(A) semiconductor, metal, superconductor
(B) metal, superconductor, semiconductor (C) metal, semiconductor, superconductor (D) superconductor, metal, semiconductor.
Figure 3. 41
44 As temperature decreases:
(A) the resistance of metals increases
(B) the resistance of semiconductors increases (C) the resistance of semiconductors decreases (D) all substances become superconductors.
45 The exclusion of a magnetic field by a superconductor is called:
(A) the photoelectric effect (B) the Meissner Effect (C) Bragg diffraction (D) ferromagnetism.
S
HORTA
NSWERQ
UESTIONSIn keeping with the format of the HSC sample marks are given for each question.
Answer the following questions in approximately three lines of writing, calculation or diagram.
152 List four properties of cathode rays. (2 marks) 153 In 1888 Hertz demonstrated two phenomena
that were to have important implications for science. These were the transmission and reception of 'radio waves' and the photoelectric effect. Explain how observations of these two phenomena support:
(a) Maxwell's electromagnetic theory of light (2 marks) and
(b) Einstein’s quantum theory. (2 marks) 154 Explain why the photoelectric effect supports the
particle model of light rather than the wave theory. (3 marks)
155 It is found that when light above a certain frequency illuminates the surface of a metal,
125 Core Topic Three: From Ideas to Implementation electrons are liberated from the metal. In an
experiment to determine how the maximum kinetic energy of the emitted electrons varies with frequency, the graph in Figure 3.42 was obtained.
Figure 3. 42
(a) Write an equation for this line. (1 mark) (b) What is the significance of the frequency
fo? (1 mark)
(c) What is the maximum kinetic energy of the emitted electrons at frequency 3 fo? (1 mark)
156 Blue light of wavelength 450 nm (1 nm = 10-9 m) is incident on a metal surface whose work function is 2.4 x 10-19 J. Calculate the maximum kinetic energy of the resulting photoelectrons.
(2 marks) (Planck's constant = 6.6 x 10-34 J.s and c = 3 x 108 m.s-1.)
157 The German physicist Heisenberg stated in 1924 that: "Light and matter are but single entities, the apparent duality of their nature lying in the limitations of language". State two experiments which show that light has:
(a) a wave nature (1 mark) and (b) a particle nature. (1 mark)
158 A wave packet can be visualised as in Figure 3.43. In what way does this picture illustrate the wave-particle duality of light? (2 marks)
Figure 3. 43
159 Cathode ray tubes (CRTs) have three main components.
(a) What are these components? (2 marks) (b) What is the purpose of each of them?
(3 marks)
160 Briefly describe how lightning rods work.
(3 marks)
161 In 1900 the German physicist Max Planck hypothesised that energy is quantised?
(a) What phenomenon led Planck to this conclusion? (1 mark)
(b) Explain why he made this proposal.
(2 marks)
162 Describe how the photoelectric effect is used in one of the following:
(a) photocell (1 mark) (b) solar cell (1 mark) (c) breathalyser. (1 mark)
163 Light of frequency greater than the threshold frequency of lithium is shone onto a lithium surface. If the intensity of the incident light is increased, describe the effect on:
(a) the number of photoelectrons emitted (b) the maximum kinetic energy of the emitted
photoelectrons (1 mark)
(c) If the frequency is now increased above the threshold frequency and the intensity is unchanged, describe the effect on:
(i) the number of photoelectrons emitted (1 mark)
(ii) the maximum kinetic energy of the emitted photoelectrons. (1 mark) 164 Light of frequency 6.0 x 1014 Hz is incident on a
metal plate causing electrons to be emitted with a maximum kinetic energy of 1.5 x 10-19 J.
(a) What is the work function of the metal surface? (1 mark)
(b) What is the minimum frequency that will result in photoemission? (1 mark)
165 Silicon is the preferred semiconductor material in use today. Give three reasons why this is the case. (2 marks)
166 Semiconductors have all but completely replaced thermionic valves in modern electronics.
(a) What are thermionic valves? (1 mark) (b) Give three reasons why semiconductors
now predominate. (2 marks)
L
ONGERA
NSWERQ
UESTIONSIn keeping with the format of the HSC sample marks are given for each question.
Answer the following questions in approximately five lines of writing, calculation or diagram.
167 In Figure 3.44 X and Y are two parallel
horizontal metal plates separated by 10.0 mm in a vacuum. A potential difference of 100 V is maintained between the plates and the polarity is arranged such that the top plate is positive. A horizontal magnetic field of 0.04 T exists and is perpendicular to the electric field between the plates.
Figure 3. 44
A horizontal beam of electrons is fired between the plates so they enter the magnetic field at right angles.
(a) Calculate the size of the electric field between the plates. (1 mark)
(b) What is the size and direction of the electric force acting on one electron? (1 mark) (c) In which direction should the magnetic field
be directed to provide a downwards force?
(1 mark)
(d) Neglecting gravity, calculate the speed of an electron that will allow it to pass
undeflected between the plates. (2 marks) 168 In 1897, J.J. Thomson used apparatus similar
to that shown in Figure 3.45.
Figure 3. 45
He arranged for electric and magnetic fields to act on cathode rays as they passed through the tube.
(a) If the electric field acted alone, what path would the cathode rays follow in the electric field? (1 mark)
(b) Write down expressions for the force acting on the cathode rays due to both the electric field and the magnetic field. Explain the meaning of each term used. (3 marks) (c) By making these fields the same
magnitude, Thomson was able to allow the cathode rays to pass through undeflected.
From this he was able to determine the speed of the cathode ray. Explain using equations, how this was done. (2 marks) (d) Thomson showed that cathode rays had a
q/m ratio of 1.76 x 1011 C. kg-1. What is the significance of this? (2 marks)
169 Heinrich Hertz is an important figure in science as he was the first to generate electromagnetic waves.
(a) Briefly explain how Hertz demonstrated and explained the generation and detection of electromagnetic waves. (4 marks) (b) List five characteristics of these
electromagnetic waves. (2 marks)
(c) What phenomenon did Hertz discover about the use of ultraviolet light in his
experiments? (1 mark)
170 Light of wavelength 600 nm is shone onto a clean sodium surface. Sodium has a work function of 3.7 x 10-19 J.
(a) What is meant by the ‘work function’?
(1 mark)
(b) What is the energy of the light photon?
(1 mark)
(c) What happens when light shines on the surface? (1 mark)
127 Core Topic Three: From Ideas to Implementation (d) Explain what happens if the light intensity is
increased (but the wavelength is unchanged). (1 mark)
171 Briefly describe how doping a semiconductor can alter its electrical properties. In your answer state whether you are talking about p-type or n-type and ensure you state which are the majority charge carriers. (5 marks)
172 Describe the contribution of the Braggs to our understanding of the structure of matter.
(4 marks)
173 Conduction in semiconductors involves both holes and electrons.
(a) What is a hole? (1 mark)
(b) Explain how holes move. (2 marks) 174 Metals are good conductors because they have
a large number of ‘free’ electrons. In the absence of a potential difference there is no current in the conductor. When a potential difference is applied across the ends of a metal conductor, however, the electrons drift along.
(a) Describe a model of metal structure that explains the good conductivity. (2 marks) (b) Why is a potential difference needed for a
current? (2 marks)
(c) What is meant by the term ‘drift velocity’?
(1 mark)
175 The phenomenon of superconductivity was discovered in 1911.
(a) What is ‘superconductivity’? (1 mark) (b) What was the first metal to be discovered
that demonstrated this phenomenon?
(1 mark)
(c) State three current or potential uses of superconductors. (2 marks)
(d) Explain how superconductivity is used on one of the uses identified in (c) above.
(3 marks)
(e) List two advantages and two
disadvantages of currently available superconductors. (2 marks)
176 Briefly describe the BCS theory of super-conductivity. (5 marks)