Motors and Generators HSC Questions
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2001
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2002
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2003
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2004
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2005
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2006
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2007
A
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2008
C
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2009
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2010
C
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2011
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2002
9.3.1
2002
9.3.1
Question 7
A student performed an experiment to measure the force on a long current-carrying conductor placed
perpendicular to an external magnetic field. The graph shows how the force on a 1.0 m length of the
conductor varied as the current through the conductor was changed.
What was the magnitude of the external magnetic field in this experiment?
(A) 0.23 T
(B) 1.1 T
(C) 2.1 T
(D) 4.3 T
Question 8
A single-turn coil of wire is placed in a uniform magnetic field B, so that the plane of the coil is parallel
to the field, as shown in the diagrams. The coil can move freely. An electric current I flows around the
coil in the direction shown. In which direction does the coil begin to move as a consequence of the
interaction between the external magnetic field and the current?
2003
9.3.1
2003
9.3.1
Question 9
A current of 5.0 A flows in a wire that is placed in a magnetic field of 0.5 T. The wire is
0.7 m long and is at an angle of 60° to the field.
What is the approximate magnitude of the force on the wire?
(A) 0 N
(B) 0.9 N
(C) 1.5 N
(D) 1.8 N
Question 10
A flexible wire loop is lying on a frictionless table made from an insulating material. The wire can slide
around horizontally on the table and change shape freely, but it cannot move vertically. The loop is
connected to a power supply, a switch and two terminals fixed to the table as shown.
When the switch is closed, a current I flows around the loop. Which of the following diagrams most
closely represents the final shape of the loop after the switch is closed?
2003
9.3.1
2007
Question 19 (3 marks)
Two straight copper wires are suspended so that their lower ends dip into a conducting salt solution in a
beaker as shown. The length of the straight section of each wire above the conducting salt solution is 35
cm and they are placed 1.5 cm apart. The ends of the wire do not touch the bottom of the beaker. The
two wires are connected to a DC power supply.
A current of 2 amperes flows from the battery. Calculate the magnitude and direction of the initial force
on each wire.
Question 6
An electric motor is set up as shown.
9.3.1.1.6
When current is supplied the coil does not turn. Which of the following is required for the coil to start
turning?
2008
9.3.1.2.2
(A) The magnetic field must be increased.
(B) The direction of the current must be reversed.
(C) The magnitude of the current must be increased.
(D) The starting position of the coil must be changed.
Question 6
Three identical wires W1, W2 and W3 are positioned as shown. Each carries a current of the same
magnitude in the direction indicated.
What is the magnitude and direction of the resultant force on W2?
2011
9.3.1.2.2
2010
9.3.1.2.3
9.2.3.2.3
9.2.2.13
9.2.2.12
9.2.1.2.2
2004
9.3.1.2.4
Question 10
A student performed an experiment using two identical metal rods connected to a power supply. Rod A
was placed at different distances from Rod B, and the measurements on the electronic balance were
recorded.
Which is the independent variable?
(A) The length of the rods
(B) The current in Rod A
(C) The mass recorded on the balance
(D) The distance between the two rods
Question 32 (8 marks)
Two significant problems that will affect a manned spaceflight to Mars are:
• the changes in gravitational energy
• protecting the space vehicle from high-speed electrically charged particles from the Sun.
Use your understanding of physics to analyse each of these problems.
Question 10
A disc magnet has its poles on its opposing flat surfaces. An insulated copper wire was placed on the
disc magnet as shown in the diagram.
2006
9.3.1.2.2
The instant the wire was connected to a DC battery, the wire was observed to move in the direction of
the arrow. Which statement describes the direction of the magnet’s field and the direction of the current
in the wire, consistent with this observation?
(A) The field was vertically upward and the current was from X to Y.
(B) The field was vertically upward and the current was from Y to X.
(C) The field was in the direction of the arrow and the current was from X to Y.
(D) The field was in the direction of the arrow and the current was from Y to X.
Question 20 (8 marks)
A balance was used to investigate the relationship between current and force. The balance was set up
with one copper rod fixed to it and a second rod fixed above it, as shown in the diagram. Each rod was
connected to a source of current. The diagram is not to scale.
The copper rods were rigid, each was 2.6 m long, and they were parallel. The current in the upper rod
was kept constant at 50 A. Different currents were passed through the lower rod and the balance reading
recorded for each current. The readings are given in the table below.
(a) Identify the relative directions of the currents in both rods, and justify your answer. (2 marks)
(b) Plot the data from the table onto the graph, using the scales and axes as indicated, and add the line of
best fit (trend line). (2 marks)
9.3.1.2.5
(c) Find the mass of the copper rod on the balance.
(1 mark)
(d) Calculate the distance between the two copper rods. (3marks)
2006
9.3.1.2.5
Question 6
The diagram shows a magnet standing on the bottom of a dish filled with a conducting solution. A
copper wire is suspended freely from a point above the magnet with its tip in the conducting solution. It
is held in the position shown.
The switch is closed and the wire released. Which of the following will be observed?
2009
(A) The wire will rotate about the magnet.
(B) The wire will be attracted to the magnet.
(C) The magnet will rotate about its vertical axis.
(D) The solution in the dish will rotate about the magnet.
Question 11
The diagram shows a DC motor with a constant current flowing to the rotor.
9.3.1.2.5
9.3.1.2.3
9.1.13
Which pair of graphs best describes the behaviour of the force F on wire AB, and the torque τ on the
rotor as functions of time t?
2008
Question 18 (4 marks)
The diagram shows a coil in a magnetic field. The coil can rotate freely.
9.3.1.2.5
9.3.1.2.4
The coil is connected to a power supply and, at the instant shown, terminal X is positive.
2010
9.3.1.2.5
9.3.1.2.4
(a) In which direction will side PQ initially move? (1 mark)
Question 20
The diagrams show possible ways to connect the coils and rotor of a DC motor to a DC power supply.
In which circuit will the rotor turn in a clockwise direction?
2011
Question 12
The diagram represents a DC electric motor.
9.3.1.2.5
9.3.1.2.4
What is the polarity of the magnetic pole at X, and the direction of the motion of wire Y?
2009
9.3.1.2.2
9.1.14.1d
Question 23 (6 marks)
Two identical wires, W1 and W2, each 2.5 m in length, are positioned as shown. They carry identical
currents in the direction indicated.
9.3.1.3.1
9.1.13.1d
9.1.12.4b
9.3.1.2.2
9.1.14.1g
9.1.14.1f
9.1.14.1d
9.1.13.1
(a) Identify the direction of the force which W2 experiences as a result of the current in W1. (1 mark)
(b) Calculate the current in each wire, given that the two wires experience a force of 6.9 × 10–4 N. (2
marks)
(c) A third wire, W3, carrying a smaller current, is now placed as shown. (3 marks)
Explain qualitatively the forces on W2 as a result of the currents in W1 and W3.
2004
Question 21 (6 marks)
(a) The diagram shows a two-pole DC motor as constructed by a student.
9.3.1.3.2
Identify THREE mistakes in the construction of this DC motor as shown in the diagram. (3 marks)
2011
9.3.1.3.3
9.3.1.2.5
Question 27 (4 marks)
A single turn coil is positioned in a region of uniform magnetic field with a strength of 0.2 T. The plane
of the coil is at 45° to the magnetic field. The coil is a square with 5 cm sides, and carries a current of
10.0 A.
(a) Calculate the magnitude of the force on side AB. (2 marks)
(b) Explain why the net force produced by the magnetic field on the coil is zero. (2 marks)
2006
9.3.1.3.3
9.1.2.1
2010
9.3.1.3.3
9.3.1.2.1
2001
9.3.1.3.3
9.3.1.2.2
Question 7
A current-carrying conductor passes through a square region of magnetic field, magnitude 0.5 T, as
shown in the diagram. The magnetic field is directed into the page.
What is the magnitude of the magnetic force on the conductor?
(A) 0.170 N
(B) 0.424 N
(C) 0.600 N
(D) 0.849 N
Question 28 (4 marks)
A copper rod is placed on a wooden frame, which is placed on an electronic balance. A length of 0.2 m
of the rod passes at right angles to a horizontal magnetic field.
When a current of 0.3 A is passed through the rod, the reading on the balance increases by 7.5 × 10−4
kg. What is the strength and direction of the magnetic field?
Question 14
Two straight metal rods, P and Q, have the same length. They are each pivoted at one end and rotated
with the same angular velocity so that they sweep out horizontal circular paths as shown in diagrams X
and Y. A constant current I is flowing along each rod, as shown. In diagram X, a constant magnetic field
is applied at right angles to the plane of the circular path. In diagram Y, a uniform magnetic field of the
same magnitude is applied in the plane of the circular path.
Which of the following statements about the forces acting on rod P and rod Q is correct?
(A) The magnitude of the force on P is exactly the same as the magnitude of the force on Q at all times.
(B) The magnitude of the force on P is constant and the magnitude of the force on Q is zero.
(C) The magnitude of the force on P is constant and the magnitude of the force on Q varies with time.
(D) The magnitude of the force on P varies with time and the magnitude of the force on Q is constant.
2004
9.3.1.3.3
Question 26 (7 marks)
The diagram shows part of an experiment designed to measure the force between two parallel currentcarrying conductors.
9.3.1.2.2
The experimental results are tabulated below.
(a) Plot the data and draw the line of best fit. (3 marks)
(b) Calculate the gradient of the line of best fit from the graph. (1 mark)
(c) Write an expression for the magnetic force constant k in terms of the gradient and other variables. (2
marks)
(d) Use this expression and the gradient calculated in part (b) to determine the value of the magnetic
force constant k. (1 marks)
2001
9.3.1.3.3
9.3.1.2.3
Question 22 (7 marks)
Two parallel wires are separated by a distance of 0.75 m. Wire X is 3.0 m long and carries a current of
2.0 A. Wire Y can be considered to be infinitely long and carries a current of 5.0 A. Both currents flow
in the same direction along the wires.
(a) What is the direction of the force that exists between the two wires? (1 mark)
9.3.1.2.3
9.3.1.2.2
(b) On the axes, sketch a graph that shows how the force between the two wires would vary if the length
of Wire X was increased. (2 marks)
9.3.1.3.2
(c) In your Physics course you have performed a first-hand investigation to demonstrate the motor
effect. Explain how your results demonstrated that effect. (4 marks)
2009
9.3.1.2.1
9.1.14.1f
Question 21 (6 marks)
A rectangular wire loop is connected to a DC power supply. Side X of the loop is placed next to a
magnet. The loop is free to rotate about a pivot.
9.3.1.2.3
9.1.14.1f
9.1.13.1d
9.1.12.4b
9.3.1.3.3
9.3.1.2.3
9.1.14.1f
9.1.13.1d
9.1.12.4b
When the power is switched on, a current of 20 A is supplied to the loop. To prevent rotation, a mass of
40 g can be attached to either side X or side Y of the loop.
(a) On which side of the loop should the mass be attached to prevent rotation? (1 mark)
(b) Calculate the torque provided by the 40 g mass. (2 marks)
(c) Calculate the magnetic field strength around side X. (3 marks)
2004
9.3.1.3.4
2011
9.3.1.3.4
2007
Question 9
An electric DC motor consists of 500 turns of wire formed into a rectangular coil of dimensions 0.2 m ×
0.1 m. The coil is in a magnetic field of 1.0 × 10−3 T. A current of 4.0 A flows through the coil. What is
the magnitude of the maximum torque, and the orientation of the plane of the coil relative to the
magnetic field when this occurs?
(A) 0.04 N m, parallel to the field
(B) 0.04 N m, perpendicular to the field
(C) 0.4 N m, parallel to the field
(D) 0.4 N m, perpendicular to the field
Question 18
An electric motor is constructed using a square coil and a uniform magnetic field of strength 0.45 T.
The coil has 3 turns and sides of 10 cm. A current of 0.5 A flows through the coil. What is the
maximum torque experienced by the coil as it rotates?
(A) 2.25 × 10–3 Nm
(B) 6.75 × 10–3 Nm
(C) 22.5 Nm
(D) 67.5 Nm
Question 21 (5 marks)
A simple motor consists of a flat rectangular coil with n turns in a magnetic field B as shown.
9.3.1.3.4
9.3.1.2.4
9.3.1.2.3
9.3.1.3.4
9.3.1.2.3
9.3.1.3.4
9.3.1.2.3
The coil has an area of 0.01_m2and carries a current of 1_A. The motor drives a pulley of diameter 20
cm, and weights can be hung from either side of the pulley at point X or point Y.
(a) In order to prevent rotation, should a weight be hung at point X or at point Y? Justify your answer.
(1 mark)
(b) What is the magnitude of the torque provided by a mass of 0.2 kg suspended from either point X or
point Y? (2 marks)
(c) If the motor is just stopped by a mass of 0.2 kg, how many turns does the coil have? (2 marks)
2006
Question 19 (3 marks)
The diagram shows the structure of a typical galvanometer.
9.3.1.3.5
9.3.1.2.4
Describe how the galvanometer operates as an application of the motor effect.
2002
9.3.2
2002
Question 9
In a student experiment, a bar magnet is dropped through a long plastic tube of length l and diameter d.
The time taken for it to hit the floor is recorded.
The experiment is repeated using a copper tube of the same length and diameter.
Which of the following statements is correct?
(A) The magnet will take the same time to hit the floor in both cases.
(B) The magnet will come to rest in the middle of the copper tube.
(C) The magnet will take longer to fall through the copper tube.
(D) The magnet will take longer to fall through the plastic tube.
Question 23 (7 marks)
(a) State Lenz’s law. (1 mark)
9.3.2
(b) When the metal rod is moved upwards through the magnetic field as shown in the diagram, an emf
is induced between the two ends.
(i) Which end of the rod is negative? (1 mark)
(ii) Explain how the emf is produced in the rod. (3 marks)
(c) Explain how the principle of induction can be used to heat a conductor. (2 marks)
2003
9.3.2
Question 20 (4 marks)
Two solenoids (coils) with hollow cores are suspended using string so that they are hanging in the
positions shown below. The solenoids are free to move in a pendulum motion.
In the first investigation shown in Figure 1, a strong bar magnet is moved towards the solenoid until the
north end of the magnet enters the solenoid and then the motion of the magnet is stopped. In the second
investigation, shown in Figure 2, a thick copper wire is connected between the two terminals, A and B,
at the ends of the solenoid. The motion of the magnet is repeated exactly in this second investigation.
Explain the effect of the motion of the magnet on the solenoid in the two investigations.
2003
Question 22 (5 marks)
9.3.2
Describe a first-hand investigation to demonstrate the effect on a generated electric current when the
strength of the magnet is varied.
In your description, include:
• a labelled sketch of the experimental set-up;
• how you varied the magnetic field strength;
• how other variables were controlled.
Question 8
A square loop of wire, in a uniform magnetic field, is rotating at a constant rate about an axis as shown.
The magnetic field is directed out of the plane of the page. At time t 0 the plane of the loop is
perpendicular to the magnetic field and side XY is moving out of the page.
2006
9.3.2.2.3
Which graph best represents the variation of the magnetic flux through the loop with time?
2011
9.3.2.2.3
Question 14
A heavy copper split ring is attached by a light insulating rod to a pivot to form a pendulum. A region of
uniform magnetic field B is present as shown. As the pendulum swings from Position 1 to Position 2,
the induced emf in the ring is measured between points X and Y.
Which graph best represents the measured emf during the time that the pendulum swings from Position
1 to Position 2?
2011
9.3.2.2.4
2007
9.3.2.2.4
9.3.2.2.3
Question 6
Why is the back emf induced in a motor greater when the motor is rotating faster?
(A) A larger current is induced.
(B) It takes a greater emf to spin the motor.
(C) The rate of change of magnetic flux is greater.
(D) More magnetic field lines are being cut per rotation.
Question 7
In the graph shown, the solid curve shows how the emf produced by a simple generator varies with
time. The dashed curve is the output from the same generator after a modification has been made to the
generator.
2004
9.3.2.2.5
Which modification was made to produce the result shown?
(A) The area of the coil was doubled.
(B) A split-ring commutator was added.
(C) The speed of rotation of the coil was doubled.
(D) The number of turns in the coil was quadrupled.
Question 21 (6 marks)
(b) An ammeter was used to measure the current through a small DC motor. While it was running
freely, a current of 2.09 A was recorded. While the motor was running, the axle of the motor was held
firmly, preventing it from rotating, and the current was then recorded as 2.54 A.
Explain this observation. (3 marks)
2006
9.3.2.2.5
Question 22 (5 marks)
A student drops a bar magnet onto a large block of copper resting on the floor. The magnet
falls towards the copper, slowing down as it comes close, then landing gently.
(a) Explain the physics responsible for this observation. (3 marks)
(b) Predict what will happen if the experiment is repeated with a copper block cooled to approximately
–50°C. Justify your prediction. (2 marks)
2010
9.3.2.2.5
9.3.2.2.4
Question 11
Lawrence and William Bragg used X-rays to determine the crystal structure of materials. Which
property of waves was the basis of their technique?
(A) Diffraction
(B) Dispersion
(C) Polarisation
(D) Rarefaction
2001
9.3.2.2.6
2008
Question 21 (3 marks)
A fan that ventilates an underground mine is run by a very large d.c. electric motor. This motor is
connected in series with a variable resistor to protect the windings in the coil. When the motor is
starting up, the variable resistor is adjusted to have a large resistance. The resistance is then lowered
slowly as the motor increases to its operating speed. Explain why no resistance is required when the
motor is running at high speed, but a substantial resistance is needed when the motor is starting up.
Question 18 (4 marks)
The diagram shows a coil in a magnetic field. The coil can rotate freely.
9.3.2.2.6
The coil is connected to a power supply and, at the instant shown, terminal X is positive.
(b) When the coil starts rotating, the potential difference experienced by theelectrons in the wire is less
than that supplied by the power supply. Describe the origin of this effect. (3 marks)
2010
9.3.2.2.6
9.3.2.2.5
2001
9.3.2.2.6
9.3.2.2.5
9.3.2.2.4
8.3.2.3.5
Question 8
While drilling into a tough material, the DC motor in an electric drill is slowed significantly. This
causes its coils to overheat. Why do the coils overheat?
(A) The resistance of the coils increases significantly.
(B) The increased friction on the drill is converted to heat.
(C) The back emf decreases and so the current in the coils increases.
(D) The induced eddy currents increase and so more heat is produced.
Question 10
An electric motor is connected to a power supply of constant voltage. The motor is allowed to run at
different speeds by adjusting a brake. Which graph best shows how the current through the motor varies
with speed?
2011
Question 25 (4 marks)
Identical magnets A and B are suspended above vertical copper tubes as shown in the diagram.
9.3.2.2.7
2009
9.3.2.2.7
9.1.14.1d
2005
9.3.2.3.1
The magnets are dropped at the same time. Each magnet falls straight through its tube without touching
the tube walls. Which magnet leaves its tube first and why?
Question 7
A type of car speedometer consists of a rotating bar magnet which produces eddy currents in a copper
disc. A model of this is shown.
As the magnet begins to rotate, in which direction does the disc move?
(A) Toward the magnet
(B) Away from the magnet
(C) Rotates in the same direction as the magnet
(D) Rotates in the opposite direction to the magnet
Question 7
A single-turn coil of wire is placed in a uniform magnetic field B at right angles to the plane of the coil
as shown in the diagrams. The coil is then rotated in a clockwise direction as shown. Which of the
following shows the direction of current flow in the coil as it begins to rotate?
2005
9.3.2.3.2
2007
Question 6
In a particular experiment a long length of copper wire of very low resistance is rotated by two students.
The ends of the wire are connected to a galvanometer, G, and a current is detected.
Which of the following is LEAST likely to affect the amount of current produced?
(A) The length of the rotating wire
(B) The thickness of the rotating wire
(C) The speed with which the wire is rotated
(D) Whether the wire is oriented north-south or east-west
Question 8
The variation in magnetic flux through a coil is shown below.
9.3.2.3.2
Which graph best represents the corresponding induced emf in the coil?
2008
9.3.2.3.2
9.3.2.2.4
Question 8
A plastic cylinder with a metal strip, M, on its surface is rotated at constant speed about its axis, in a
uniform magnetic field. During each rotation the strip, M, passes locations W, X, Y and Z shown
below.
2010
When is the potential difference across M greatest?
(A) As M passes W.
(B) As M passes X.
(C) As M passes Y.
(D) As M passes Z.
Question 26 (5 marks)
A bar magnet is dropped through the centre of a solenoid connected to a data logger as shown.
9.3.2.3.2
9.3.2.2.4
9.3.2.3.2
9.3.2.2.4
The data are recorded in the graph as shown.
(a) Why is the magnitude of the potential difference at Y greater than at X? (2 marks)
(b) The magnet is dropped again with two changes being made.
1. It is dropped from a greater height. 2. The south pole of the magnet is pointing down.
Sketch a graph that represents the most likely outcome of this new experiment. (3 marks)
2008
9.3.2.3.3
2011
Question 9
Which statement best explains how induction cooktops heat food?
(A) Eddy currents generated in the water in the food produce heat.
(B) Eddy currents generated in the base of the saucepan produce heat.
(C) Resistance in the glass of the cooktop produces heat.
(D) Resistance in the element beneath the glass cooktop produces heat.
Question 11
A student set up the equipment shown to carry out a first-hand investigation.
9.3.2.3.3
9.3.2.3.2
2007
9.3.2.3.4
2001
9.3.2.3.4
9.3.2.2.7
What was the student investigating?
(A) Gravity
(B) The motor effect
(C) Magnetic levitation
(D) Electromagnetic induction
Question 9
A stationary exercise bike has a solid metal wheel that is rotated by a chain connected to the pedals. An
array of strong permanent magnets provides a magnetic field close to the face of the wheel. The
exercise level can be selected from 1(easy) to 6(hard) using a control panel.
When level 6 is selected, which of the following statements is correct?
(A) The current supplied to the bike is a minimum.
(B) The magnetic field at the wheel is a minimum.
(C) The induced current in the wheel is a maximum.
(D) The distance between the magnets and the wheel is a maximum.
Question 8
A light rod has a coil of insulated copper wire fixed at one end and is pivoted at the other end. The
result is a pendulum which is free to swing back and forth. A magnet is placed underneath this
pendulum. The arrangement is shown in the diagram.
The pendulum is pulled back and then allowed to swing. Which of the following would cause the
pendulum to come to rest most quickly?
(A) Replacing the magnet with a stronger one
(B) Shortening the pendulum
(C) Replacing the rod with a heavier one
(D) Connecting the ends of the coil by a piece of copper wire
2005
Question 9
Three rings are dropped at the same time over identical magnets as shown below.
9.3.2.3.4
9.3.2.2.7
2005
9.3.2.3.4
9.3.2.3.3
2002
Which of the following describes the order in which the rings P, Q and R reach the bottom of the
magnets?
(A) They arrive in the order P, Q, R.
(B) They arrive in the order P, R, Q.
(C) Rings P and R arrive simultaneously, followed by Q.
(D) Rings Q and R arrive simultaneously, followed by P.
Question 20 (6 marks)
In your course you had to gather information to explain how induction is used in certain applications.
With reference to TWO applications, describe how you assessed the reliability of information you
found.
Question 10
The coil of an AC generator rotates at a constant rate in a magnetic field as shown.
9.3.3
Which of the following diagrams represents the curve of induced emf against position?
2002
Question 22 (6 marks)
Two types of generator are shown in the diagram.
9.3.3
(a) What is the function of the brush in a generator? (1 mark)
(b) Which of these generators is a DC generator? Justify your choice. (3 marks)
(c) Outline why AC generators are used in large-scale electrical power production. (2 marks)
2003
Question 6
The diagram shows a DC generator connected to a cathode ray oscilloscope (CRO).
9.3.3
What output voltage would be observed for this generator on the CRO?
2006
Question 9
Early electric generators were often very simple. A hand-operated version is depicted below.
9.3.3.2.1
2009
9.3.3.2.1
2007
9.3.3.2.2
2004
Brush X touches the metal axle and Brush Y touches the rim of the disc. If the metal disc is rotated
uniformly as shown, which statement about the current through the globe is correct?
(A) No current flows.
(B) A direct current flows from Y to X.
(C) A direct current flows from X to Y.
(D) An alternating current flows between X and Y.
Question 6
Which of the following would increase the output of a simple DC generator?
(A) Increasing the rotation speed of the rotor
(B) Reducing the number of windings in the coil
(C) Using slip rings instead of a split ring commutator
(D) Wrapping the windings around a laminated, aluminium core
Question 25 (4 marks)
A student claims that a DC generator is an ‘electric motor in reverse’. Analyse this claim with reference
to the structure and function of a simple DC generator and an electric motor. Include diagrams in your
answer.
Question 22 (3 marks)
The photograph below shows parts of an AC electric motor.
9.3.3.2.3
Describe the main features of this type of motor and its operation.
2001
Question 4
Two types of generator are shown.
9.3.3.2.3
9.3.3.2.1
What type of current is produced by each generator when connected to an external resistance?
2005
(A) Both produce d.c.
(B) Both produce a.c.
(C) Generator 1 produces d.c. and Generator 2 produces a.c.
(D) Generator 1 produces a.c. and Generator 2 produces d.c.
Question 21 (6 marks)
Two thin metal tubes one metre long were supported in a vertical wooden rack as shown in the diagram.
9.3.3.2.4
9.3.1.3.1
9.3.1.2.2
The two ends were connected together, then the other two ends were connected briefly to a car battery
as shown in the diagram. It was observed that one of the tubes jumped upward as the connection was
made.
(a) Explain why only one tube jumped upward. (2 marks)
(b) Each tube has a mass of 1 × 10-2 kg, and the tubes lie on the rack 10 cm apart. What minimum
current flows when one tube jumps? (3 marks)
(c) What is the implication of this result for power distribution networks? (1 mark)
2001
9.3.3.2.5
Question 23 (6 marks)
Discuss the effects of the development of electrical generators on society and the environment.
2011
9.3.3
Question 26 (9 marks)
(a) Use a flowchart to show how electrical energy is transferred from a power station to its point of use.
(3 marks)
9.3.3.2.5
(b) Discuss the effects on the environment of the development of AC generators. (6 marks)
2008
9.3.3.3.1
9.3.3.2.3
Question 25 (5 marks)
The diagrams show two different types of generator spinning at the same number of revolutions per
minute. The difference between the two generators is in the way they are connected to the external
circuits.
9.3.3.2.3
(a) On the axes below, sketch a voltage-time graph for each generator. (2 marks)
(b) Explain how the difference in connection to the external circuit accounts for the different output
voltages. (3 marks)
2007
9.3.3.3.2.1
9.3.3.2.5
Question 20 (4 marks)
Assess the effects of the development of AC generators on today’s society and the environment.
2008
9.3.3.3.3
9.3.3.3.2
9.3.3.2.5
9.2.2.3.3
2004
9.3.3.3.3
9.3.3.3.2
9.3.3.2.5
9.3.3.2.4
9.3.3.2.3
9.3.3.1
2004
9.3.3.3.4
Question 21 (6 marks)
‘The work of scientists is influenced by external factors.’ Do you agree?
Justify your answer with reference to the work of a scientist in the development of
•space exploration
OR
•large-scale electricity distribution systems.
Question 24 (6 marks)
In the late nineteenth century Westinghouse and Edison were in competition to supply electricity to
cities. This competition led to Edison holding public demonstrations to promote his system of DC
generation over Westinghouse’s system of AC generation. Propose arguments that Westinghouse could
have used to convince authorities of the advantages of his AC system of generation and distribution of
electrical energy over Edison’s DC supply.
Question 20 (2 marks)
The photograph below shows a transmission line support tower. The inset shows details of the top
section of the tower.
Describe the role of each of the parts labelled A and B in the photograph.
2010
Question 10
The diagram shows a model of a transformer in a circuit.
9.3.3.3.4
9.3.3.2.4
Which of the following correctly identifies Part 1 and Part 2 and the function of this transformer?
2002
9.3.4
2003
9.3.4
2003
9.3.4
Question 6
What is the role of a transformer at an electrical power station?
(A) To reduce heating in the transmission lines by stepping up the voltage
(B) To reduce heating in the transmission lines by stepping up the current
(C) To increase heating in the transmission lines by stepping up the voltage
(D) To increase heating in the transmission lines by stepping up the current
Question 8
A neon sign requires a 6000 V supply for its operation. A transformer allows the neon sign to operate
from a 240 V supply. What is the ratio of the number of secondary turns to the number of primary turns
for the transformer?
(A) 1 : 40
(B) 1 : 25
(C) 25 : 1
(D) 40 : 1
Question 21 (5 marks)
(a) Explain the relationship between the current in the primary coil and the current in the secondary coil
of an ideal step-down transformer in relation to the conservation of energy. (3 marks)
(b) Explain why a transformer will work in an AC circuit but not in a DC circuit. (2 marks)
2006
Question 10
The apparatus shown is designed to investigate the operation of a transformer.
9.3.4.2.2
A student closes the switch for a short time, then opens it. The data logger records values of voltage for
both coils for the duration of the investigation. The data logger software displays the results as a pair of
voltage–time graphs on a computer monitor.
Which pair of graphs best depicts the student’s results?
2009
9.3.4.2.2
2008
9.3.4.2.3
Question 9
A thin solid conductor with sides PQRS is moving at constant velocity v, at right angles to a uniform
magnetic field B, directed into the page as shown.
Which side of the conductor has the greatest concentration of electrons?
(A) P
(B) Q
(C) R
(D) S
Question 26 (3 marks)
An induction coil is a type of transformer that allows a small voltage to be stepped up to a
higher voltage. An induction coil consists of a primary coil wound around an iron core and a
secondary coil. The secondary coil can be moved sideways so that different lengths of the iron
core are within the secondary coil.
The photographs show an induction coil with the secondary coil in two different arrangements with the
power supply turned off. At sufficiently high voltages a spark can be produced between the secondary
coil electrodes.
(a) Which arrangement would produce a spark when the power supply is turned on? Justify your choice.
(1 mark)
(b) Explain how different voltages are induced when the secondary coil is moved to different positions.
(2 marks)
2011
9.3.4.2.4
Question 5
Which law best applies to the operation of an electrical transformer?
(A) Conservation of Mass
(B) Conservation of Energy
(C) Conservation of Charge
(D) Conservation of Momentum
2001
9.3.4.2.5
9.3.4.2.4
9.3.4.2.3
2005
9.3.4.3.1
Question 11
A transformer has a primary coil with 60 turns and a secondary coil with 2300 turns. If the primary
voltage to the transformer is 110 V, what is the secondary voltage?
(A) 2.4 × 10–4 V
(B) 2.4 × 102 V
(C) 1.3 × 103 V
(D) 4.2 × 103 V
Question 8
The primary coil of a transformer is connected to a battery, a resistor and a switch. The secondary coil
is connected to a galvanometer.
Which of the following graphs best shows the current flow in the galvanometer when the switch is
closed?
2010
9.3.4.3.1
2004
9.3.4.3.2
Question 9
Why is high voltage used to transmit electrical energy from power stations to users?
(A) It helps to protect the system from lightning strikes.
(B) It allows the supporting structures to have smaller insulators.
(C) It minimises the effects of the electrical resistance of the wires.
(D) It ensures that, even with voltage losses, 240 V will still reach the user.
Question 8
A transformer which has 60 turns in the primary coil is used to convert an input of 3 V into an output of
12 V. Which description best fits this transformer?
2005
9.3.4.3.3
2007
9.3.3.3.2
Question 10
A transformer is to be designed so that it is efficient, with heating by eddy currents minimised. The
designer has some iron and insulating material available to build the transformer core. The windings are
to be made with insulated copper wire. Which of the following designs minimises the energy losses in
the core?
Question 26 (6 marks)
An electricity substation delivers a current of 10 A at a voltage of 6kV to an office complex. The office
complex uses a transformer to provide a current of 230 A at a voltage of 240V.
9.3.4.3.3
9.3.4.2.4
8.3.4.3.2
(a) Explain why AC is preferable to DC as an input current for transformers. (2 marks)
(b) Outline possible causes of energy loss in the transformer. (2 marks)
(c) Calculate the energy lost by the transformer in eight hours. (2 marks)
2008
9.3.4.3.4
Question 22 (3 marks)
Explain why the development of transformers was necessary to enable the large- scale distribution of
electrical power.
2001
9.3.4.3.4
9.3.4.2.5
9.3.4.2.4
9.3.4.2.2
9.3.4.2.1
9.3.4.1
2006
9.3.4.3.4
9.3.4.3.3
2004
9.3.4.3.6
2003
9.3.5
2004
9.3.5.2.1
9.3.2.3.4
9.3.2.2.5
Question 20 (4 marks)
The electrical supply network uses a.c. and a variety of transformers between the generating stations
and the final consumer. Explain why transformers are used at various points in the network.
Question 24 (3 marks)
Discuss the origins of unwanted heat production in transformers and ways in which these can be
overcome.
Question 7
Why do some electrical appliances in the home need a transformer instead of operating directly from
mains power?
(A) They require a voltage lower than the mains voltage.
(B) They require a source of energy that is DC rather than AC.
(C) They require an alternating current at a frequency other than 50 Hz.
(D) They consume less energy than a similar device without a transformer.
Question 7
A non-magnetic metal disk is balanced on a support as shown in the diagram below. The disk is initially
stationary. A magnet is moved in a circular path just above the surface of the disk, without touching it.
As a result of this movement the disk begins to rotate in the same direction as the magnet. The observed
effect demonstrates the principle most applicable to the operation of the
(A) DC motor.
(B) galvanometer.
(C) generator.
(D) induction motor.
Question 11
An electromagnet is attached to the bottom of a light train which is travelling from left to right, as
shown.
When a large current is passed through the coils of the electromagnet, the train slows down as a direct
result of the law of conservation of energy. In which of the following devices is the law of conservation
of energy applied in the same way?
(A) DC motor
(B) Loudspeaker
(C) Induction motor
(D) Induction cooktop
2008
9.3.5.3.1
9.3.5.2.1
2009
9.3.5.3.2
9.3.4.2.6
9.3.1.3.5
9.1.13.1a
Question 7
Which of the following is necessary for the operation of an AC induction motor?
(A) A fixed magnetic field in the rotor
(B) A direct current supply to the rotor
(C) A changing magnetic field in the rotor
(D) Split rings conducting current to the rotor
Question 20 (4 marks)
Draw a table to summarise the energy transformations and transfers for three household appliances.
Each appliance must have a different type of useful energy output. Include the name of the appliance,
its use and the transformation/transfer of energy involved.