D.4 Induction
Practice exam-style IB Physics questions for Induction, aligned with the syllabus and grouped by topic.
Question 1
A circular coil of area is in a uniform magnetic field of flux density . The normal to the coil makes an angle of with the field.
A.
$1.7 imes10^{-3}\, ext{Wb}$
B.
$8.0 imes10^{-3}\, ext{Wb}$
C.
$1.0 imes10^{-3}\, ext{Wb}$
D.
$2.0 imes10^{-3}\, ext{Wb}$
Question 2
What is the SI unit of magnetic flux?
A.
volt metre
B.
weber
C.
newton per ampere
D.
tesla
Question 3
The graph shows the magnetic flux linkage through a coil varying with time. The graph is a straight line with negative gradient.
A.
It is constant and positive for the sign convention of the graph.
B.
It reverses direction halfway through the interval.
C.
It is zero because the flux linkage is decreasing uniformly.
D.
It increases because the flux linkage is becoming smaller.
Question 4
A straight conductor of length moves at at right angles to a uniform magnetic field of flux density .
A.
$0.030\, ext{V}$
B.
$1.2\, ext{V}$
C.
$3.3\, ext{V}$
D.
$0.30\, ext{V}$
Question 5
A current in a coil is increasing.
A.
In the direction that increases the current further.
B.
At right angles to the current.
C.
In the direction that opposes the increase in current.
D.
There is no self-induced emf until the current is steady.
Question 6
A coil has 200 turns. The magnetic flux through each turn changes by in .
A.
$6.0 imes10^{-2}\, ext{V}$
B.
$1.5 imes10^{-2}\, ext{V}$
C.
$30\, ext{V}$
D.
$3.0\, ext{V}$
Question 7
A bar magnet and a conducting loop move along the same straight line with the same velocity, maintaining a constant separation and orientation.
A.
Alternating, because the field of the magnet is non-uniform.
B.
Maximum, because the magnet is aligned with the loop axis.
C.
Zero, because the magnetic flux through the loop is constant.
D.
Non-zero, because both objects are moving.
Question 8
A diagram represents a magnetic field using field lines.
A.
Field lines drawn closer together.
B.
Field lines crossing each other more often.
C.
Field lines drawn with greater thickness.
D.
Field lines drawn with more labels.
Question 9
A rectangular coil has sides and . It is placed in a uniform magnetic field of flux density . The normal to the coil makes an angle of with the magnetic field.
Calculate the area of the coil in .
[1]
Calculate the magnetic flux through the coil.
[1]
Question 10
A coil is connected to a centre-zero galvanometer. A bar magnet is held stationary near the coil.
State the galvanometer reading while the magnet is stationary.
[1]
Outline why the reading changes when the magnet is moved towards the coil.
[1]
Question 11
Distinguish between magnetic flux density and magnetic flux.
State the meaning of magnetic flux density.
[1]
State how magnetic flux depends on the orientation of an area in a uniform field.
[1]
Question 12
A north pole of a magnet moves towards the left-hand face of a circular coil. The coil is connected to a resistor so that current may flow.
A.
Clockwise, so the near face of the coil is a south pole.
B.
Anticlockwise, so the near face of the coil is a north pole.
C.
Clockwise, so the near face of the coil is a north pole.
D.
Anticlockwise, so the near face of the coil is a south pole.
Question 13
A rectangular conducting loop moves at constant velocity wholly inside a large region of uniform magnetic field. Its plane is perpendicular to the magnetic field.
A.
Zero, because no side of the loop cuts magnetic field lines.
B.
Non-zero and alternating, because the loop has two opposite sides.
C.
Non-zero and constant, because all sides cut magnetic field lines.
D.
Zero, because the magnetic flux linkage of the loop is constant.
Question 14
A coil rotates at constant angular speed in a uniform magnetic field. At an instant, the magnetic flux linkage through the coil has its maximum positive value.
A.
Half the peak value, because the coil is rotating steadily.
B.
Maximum positive, because the flux linkage is maximum positive.
C.
Zero, because the gradient of flux linkage with time is zero.
D.
Maximum negative, because of the minus sign in Faraday's law.
Question 15
A generator coil rotates in a uniform magnetic field. The rotation frequency is doubled while , and are unchanged.
A.
Peak emf is unchanged and output frequency doubles.
B.
Peak emf quadruples and output frequency doubles.
C.
Peak emf doubles and output frequency doubles.
D.
Peak emf doubles and output frequency is unchanged.
Question 16
An aircraft with wingspan flies horizontally at . The vertical component of Earth's magnetic field is .
A.
$0.020\, ext{V}$
B.
$3.2\, ext{V}$
C.
$5.6 imes10^{4}\, ext{V}$
D.
$0.41\, ext{V}$
Question 17
A generator is harder to turn when a lamp connected to it is switched on.
A.
The generator coil has a larger area when the lamp is switched on.
B.
The flux through the coil becomes constant when current flows.
C.
The lamp increases the magnetic field of the permanent magnets.
D.
The induced current produces a torque opposing the rotation.
Question 18
A 120-turn coil experiences a uniform change of magnetic flux through each turn from to in .
State Faraday's law for the magnitude of the average induced emf.
[1]
Calculate the magnitude of the average induced emf.
[1]
Question 19
A metal ring falls vertically through a region of horizontal magnetic field.
Explain why an emf is induced while the ring enters the field region.
[1]
State what happens to the induced emf when the ring is completely inside a uniform part of the field and falling at constant orientation.
[1]
Question 20
A conducting rod of length moves at right angles to a magnetic field of flux density . The induced emf is .
Calculate the speed of the rod.
[1]
State one condition required for the equation used in
[1]
to apply.
[1]
Question 21
A long solenoid is connected to a variable power supply. A small search coil is placed inside the solenoid and connected to a voltmeter.
State the voltmeter reading when the current in the solenoid is constant.
[1]
Explain why the voltmeter shows a reading while the solenoid current is increasing steadily.
[1]
Question 22
A current in an isolated coil is reduced rapidly to zero by opening a switch.
State what self-induction means in this context.
[1]
Explain the direction of the self-induced emf as the current decreases.
[1]
Question 23
A simple ac generator consists of a coil rotating between magnetic poles.
State the purpose of slip rings and brushes in this generator.
[1]
Outline why the induced emf alternates.
[1]
Question 24
A flat coil is rotated slowly in a uniform magnetic field. The graph shows magnetic flux through one turn against the angle between the field and the normal to the coil.
State the angle at which the magnitude of the flux is maximum.
[1]
State the angle at which the flux is zero.
[1]
Explain why the graph is not linear.
[1]
Question 25
A conducting rod is pulled to the right on rails in a uniform magnetic field directed into the page. The circuit is closed through a resistor.
A.
To the right, increasing the speed of the rod.
B.
Up the page, towards the upper rail.
C.
To the left, opposing the motion of the rod.
D.
Down the page, towards the lower rail.
Question 26
A coil rotating in a uniform magnetic field has induced emf
A.
$\dfrac{\pi}{\omega}$
B.
$0$
C.
$\dfrac{\pi}{2\omega}$
D.
$\dfrac{2\pi}{\omega}$
Question 27
A conducting rod slides to the right on rails connected by a resistor. A uniform magnetic field is directed out of the page.
Determine the direction of the conventional current in the rod.
[1]
Explain why an external force is needed to keep the rod moving at constant speed.
[1]
Question 28
A generator coil has 80 turns and area . It rotates at in a uniform magnetic field of flux density .
Calculate the angular speed of the coil.
[1]
Calculate the peak induced emf.
[1]
State the value of the induced emf when the flux linkage is a maximum.
[1]
Question 29
Two identical generator coils rotate in the same uniform magnetic field. Coil X rotates at frequency and coil Y rotates at frequency .
Compare the peak emf of Y with that of X.
[1]
Compare the period of the output emf of Y with that of X.
[1]
Explain both comparisons.
[1]
Question 30
A rectangular coil moves at constant speed into, through and out of a region of uniform magnetic field. The plane of the coil is perpendicular to the field.
Sketch the variation of induced emf with time for the complete motion.
[1]
State why the emf is zero while the coil is entirely inside the field.
[1]
Question 31
A rectangular loop of width and resistance is pulled at constant speed out of a uniform magnetic field of flux density . The side of length cuts the boundary of the field.
Calculate the induced emf while the loop is leaving the field.
[1]
Calculate the induced current.
[1]
State the direction of the induced effect according to Lenz's law.
[1]
Question 32
An engineer must increase the peak emf of a grid-connected generator without changing the output frequency.
State why increasing the rotation frequency is not suitable.
[1]
Suggest two changes that could increase the peak emf without changing the frequency.
[1]
Question 33
A search coil is connected to a data logger. The graph shows the variation of magnetic flux linkage with time.
Determine the induced emf during the first straight-line section.
[1]
State the induced emf during the horizontal section.
[1]
Explain why the sign of the induced emf changes in the final straight-line section.
[1]
Question 34
A conducting rod slides along rails in a uniform magnetic field. The table gives the measured emf for different speeds of the rod.
Describe the relationship between induced emf and speed.
[1]
Use the graph/table to determine the magnetic flux density. The rod length in the field is .
[1]
Suggest one reason why the data may not pass exactly through the origin.
[1]
Question 35
A coil rotates in a uniform magnetic field. The graph shows the induced emf against time for several cycles.
Determine the period of rotation of the coil.
[1]
Determine the peak emf.
[1]
Use the graph to determine the angular speed of rotation.
[1]
State the phase of the flux linkage when the emf is zero.
[1]
Question 36
A coil with different numbers of turns is moved in the same way through the same magnetic-field region. The table shows the average induced emf for each number of turns.
| Number of turns, N | Average induced emf over 0.050 s / V |
|---|---|
| 40 | 0.120 |
| 60 | 0.180 |
| 80 | 0.240 |
| 100 | 0.300 |
| 120 | 0.360 |
Describe the relationship between average induced emf and number of turns.
[1]
Determine the change in flux through one turn during the motion, using the duration shown in the table heading.
[1]
State one assumption needed for this analysis.
[1]
Question 37
The magnetic flux linkage in a rotating coil is given by
.
Determine the maximum flux linkage.
[1]
Determine the angular frequency of rotation.
[1]
Determine the peak induced emf.
[1]
Question 38
A rectangular coil is pulled at constant speed through a region of uniform magnetic field. The graph shows the induced emf as a function of time.
Identify the time interval during which the coil is wholly inside the magnetic field.
[1]
Compare the magnitudes of the emf during entry and exit.
[1]
Explain the signs of the emf during entry and exit.
[1]
Suggest how the graph would change if the speed were doubled.
[1]
Question 39
A student investigates a rotating-coil generator. The graph shows peak emf against rotation frequency.
Describe the trend shown by the graph.
[1]
Use the graph to determine for the generator.
[1]
Evaluate whether the data support the model .
[1]
Question 40
A magnet oscillates vertically above a conducting coil connected to a resistor. The graph shows the induced current in the coil as a function of time for one oscillation.
Identify an instant when the magnetic flux through the coil is changing most rapidly.
[1]
Explain why the current changes sign during the oscillation.
[1]
Suggest why the amplitude of the mechanical oscillation decreases more rapidly when the resistor is connected.
[1]
Question 41
A conducting disc swings like a pendulum between the poles of a magnet. The table compares the time for the amplitude to halve in three cases: no slots, radial slots cut in the disc, and an insulating disc of the same size.
| Disc | Half-time / s | Unc. / s |
|---|---|---|
| Conductor: no slots | 2.8 | 0.2 |
| Conductor: radial slots | 7.4 | 0.4 |
| Insulator | 25 | 2 |
Identify which case shows the strongest electromagnetic damping.
[1]
Explain why cutting radial slots changes the damping.
[1]
Evaluate whether the results are consistent with Lenz's law.
[1]
Question 42
Electromagnetic induction can be produced in several different ways.
State Faraday's law and define magnetic flux linkage.
[1]
Discuss three different methods of producing an induced emf, making clear what changes in each case.
[1]
Question 43
Lenz's law is often described as a consequence of conservation of energy.
State Lenz's law and apply it to a north pole moving away from a coil.
[1]
Discuss why an induced current that assisted the change in flux would violate conservation of energy.
[1]
Question 44
The graph shows both magnetic flux linkage and induced emf for a rotating coil. One curve is sinusoidal and the other is shifted by a quarter period.
Identify which curve represents induced emf.
[1]
Explain the phase relationship between flux linkage and induced emf.
[1]
Determine whether the rotation is at constant angular speed.
[1]
Question 45
A conducting rod is pulled at constant speed along horizontal conducting rails connected to a resistor. The rails are in a uniform magnetic field perpendicular to their plane.
Derive an expression for the magnitude of the induced emf in the rod.
[1]
Explain, using Lenz's law and energy conservation, why an external force is required to maintain constant speed when the circuit is closed.
[1]
Question 46
A coil rotates at constant angular speed in a uniform magnetic field.
Describe how the magnetic flux linkage varies during one complete rotation.
[1]
Compare and contrast the variation of flux linkage with the induced emf, including their phase relationship and dependence on rotation frequency.
[1]
Question 47
A remote generator must supply a larger peak emf to a load while maintaining the same alternating-current frequency.
Use the generator equation to identify factors affecting the peak emf.
[1]
Evaluate possible ways to increase the peak emf without changing the output frequency.
[1]
Question 48
A rectangular conducting coil is moved at constant speed into and then out of a uniform magnetic field region.
Explain why the induced emf has different values during entry, while fully inside the field, and during exit.
[1]
Explain how the magnitude and direction of the induced current would change if the coil speed were increased and its resistance were doubled.
[1]
Question 49
A coil is used as a magnetic-field sensor. The coil can be rotated and moved through different magnetic-field regions.
Explain the meaning of magnetic flux and magnetic flux linkage, including the role of the angle in .
[1]
Explain how measurements of induced emf can be used to infer changes in magnetic flux, and comment on the limitation of representing flux using field-line diagrams.
[1]
Question 50
A student claims: "A conductor moving in a magnetic field always has an induced current, because it cuts magnetic field lines."
Explain the conditions under which a motional emf is produced in a straight conductor.
[1]
Evaluate the student's claim for an isolated rod, a complete loop wholly inside a uniform field, and a loop entering a field region.
[1]
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