Magnetism and ElectromagnetismIB MYP Physics: Topic test

20 questions, 54 marks

IB MYP Physics

Magnetism and Electromagnetism topic test

Total 54 marks

Name

Class

Date

1
Two bar magnets lie on a table in a classroom in Kyoto, with their north poles facing each other 3 cm apart. A student places a small plotting compass between them. She also has an unmagnetised steel rod.
(a)
What happens between the two magnets?
[1 mark]
AThey attract each other
BThey repel each other
CNothing happens, because the magnets are too far apart
DThey attract each other first and then repel
(b)
In which direction are magnetic field lines drawn outside a magnet?
[1 mark]
AFrom the south pole to the north pole
BAlways parallel to the bar
CAway from both poles
DFrom the north pole to the south pole
(c)
Explain how the student could show that the steel rod is a magnet and not just an unmagnetised piece of steel.
[2 marks]
Total for question 1: 4 marks
2
An electric bell contains a coil of wire wound around a soft iron core. When the bell push is pressed, a current flows in the coil and the core attracts an iron armature that carries a hammer. As the armature moves, it breaks the circuit, so the hammer springs back and the circuit is made again.
(a)
Why is soft iron used for the core instead of steel?
[1 mark]
ASoft iron is a better insulator
BSoft iron is permanently magnetised
CSoft iron is magnetised easily and loses its magnetism quickly when the current stops
DSoft iron is lighter than steel
(b)
What happens to the electromagnet when the armature moves and breaks the circuit?
[1 mark]
AIt loses its magnetism, so the armature springs back
BIt becomes stronger, so the armature is held
CIt reverses its poles
DIt stays magnetised, because the core is iron
(c)
Give two ways to make the electromagnet stronger without changing the core.
[2 marks]
Total for question 2: 4 marks
3
A small loudspeaker in a radio in Lagos has a coil of wire attached to a paper cone. The coil sits in the field of a permanent magnet. The amplifier sends an alternating current through the coil.
(a)
Explain how the loudspeaker produces sound.
[3 marks]
(b)
Explain two ways to increase the force on the coil, and state which property of the sound increases as a result.
[4 marks]
Total for question 3: 7 marks
4
A wind farm in Denmark has turbines that turn a.c. generators. Each generator is a coil of wire that turns between the poles of strong magnets. The farm produces 1.1 MW (1.1 × 10⁶ W) of electrical power at 11 kV (11 000 V). The electricity is sent to a town along cables with a total resistance of 5.0 Ω. Engineers compare sending the power at 11 kV with sending it at 110 kV after a step-up transformer.
(a)
Explain how a generator produces an alternating current and how its output could be increased.
[6 marks]
(b)
Calculate the current in the cables and the power lost in the cables when the power is sent at 11 kV and at 110 kV. Explain why the engineers choose the higher voltage.
[6 marks]
Total for question 4: 12 marks
5
A model railway controller in Munich contains an ideal transformer. The primary coil has 2300 turns and is connected to the 230 V a.c. mains. The secondary coil has 200 turns.
(a)
What is the output potential difference of the transformer?
[1 mark]
A20 V
B2645 V
C230 V
D200 V
(b)
What type of transformer is this?
[1 mark]
AStep-up, because the secondary has fewer turns than the primary
BStep-up, because the secondary has more turns than the primary
CStep-down, because the secondary has fewer turns than the primary
DStep-down, because the secondary has more turns than the primary
(c)
Explain why the transformer would give no output if the primary coil were connected to a 12 V d.c. battery.
[2 marks]
Total for question 5: 4 marks
6
A toy fan in Sydney is driven by a small d.c. motor. The motor has a rectangular coil between two curved magnets, a split-ring commutator and carbon brushes, and it is powered by a battery.
(a)
What is the purpose of the split-ring commutator?
[1 mark]
ATo keep the current constant in the coil
BTo increase the voltage of the battery
CTo make the magnets turn with the coil
DTo reverse the current in the coil every half turn so that it keeps turning in the same direction
(b)
Which change would make the motor spin faster?
[1 mark]
AReversing the battery connections
BIncreasing the current in the coil
CUsing weaker magnets
DUsing a battery with a lower voltage
(c)
State what the thumb, the first finger and the second finger show in Fleming's left-hand rule.
[2 marks]
Total for question 6: 4 marks
7
A bicycle dynamo in Amsterdam is pressed against the tyre. As the wheel turns, it generates an alternating output with a peak voltage of 6.0 V. One complete cycle takes 0.020 s.
(a)
Calculate the frequency of the output.
[3 marks]
(b)
The cyclist doubles her speed. Describe how the peak voltage, the frequency and the period of the output change, and state one way in which the output differs from the d.c. output of a cell.
[4 marks]
Total for question 7: 7 marks
8
A city plans a maglev (magnetic levitation) train line. The train carries powerful electromagnets, and electromagnets along the track are arranged so that like poles face each other, which lifts the train a few centimetres above the track. The line would be built through crowded residential areas and would cost far more per kilometre than an ordinary railway.
(a)
Explain why electromagnets rather than permanent magnets are used to lift the train, and how their strength is controlled.
[6 marks]
(b)
Discuss whether the city should build the maglev line.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).