Topic 11 Practice Paper: Magnetism and electromagnetic effects — question paper

Section A: Multiple-choice questions[10 marks]

Choose one answer for each question. Each question is worth 1 mark.

1. 1

   An unmagnetised iron nail is brought near the north pole of a strong magnet. The far end of the nail becomes

   1. Aan N pole at both ends
   2. Ba south pole
   3. Ca north pole
   4. Ddemagnetised
   ( )
2. 2

   Which material is suitable for the core of a permanent magnet?

   1. ASteel
   2. BSoft iron
   3. CCopper
   4. DPlastic
   ( )
3. 3

   The magnetic field lines between two unlike poles facing each other

   1. Abend away from the gap
   2. Bdo not exist between poles
   3. Cform circles around the poles
   4. Drun almost straight from the N pole to the S pole
   ( )
4. 4

   The strength of a magnetic field is shown by

   1. Athe length of the field lines
   2. Bthe closeness of the field lines
   3. Cthe colour of the field lines
   4. Dthe arrows on the field lines
   ( )
5. 5

   The magnetic field inside a current-carrying solenoid is strongest and most uniform

   1. Aat one end
   2. Boutside the coil
   3. Calong the central axis inside the coil
   4. Dat the connecting wires
   ( )
6. 6

   A wire is moved horizontally through a vertical magnetic field. If the wire is moved twice as fast, the induced e.m.f. is

   1. Adoubled
   2. Bhalved
   3. Cthe same
   4. Dzero
   ( )
7. 7

   In a simple a.c. generator, slip rings and brushes are used to

   1. Areverse the current every half turn
   2. Bkeep the coil from spinning
   3. Cincrease the magnetic field
   4. Dconnect the rotating coil to the external circuit without twisting the wires
   ( )
8. 8

   A current-carrying wire lies in a strong magnetic field. Reversing only the current direction makes the force on the wire

   1. Adouble in size
   2. Breverse direction
   3. Cstay the same
   4. Ddisappear
   ( )
9. 9

   A transformer steps 230 V down to 12 V. The primary has 920 turns. The number of secondary turns is

   1. A48
   2. B17 600
   3. C12
   4. D230
   ( )
10. 10

    Electricity is transmitted at high voltage chiefly so that

    1. Athe cables can be thinner without melting
    2. Bhomes receive alternating current
    3. Cthe current, and hence the I²R heating loss, is smaller for the same power
    4. Dtransformers are not needed anywhere
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided.

1. 11

   A bar magnet is hung from a thread so it can swing freely, and another bar magnet is brought close to it.

   1. (a)

      The hanging magnet’s north pole turns away from the approaching end of the second magnet. State the pole of the second magnet that is nearest, and explain.

      [2]
   2. (b)

      Draw or describe the magnetic field pattern between two unlike poles facing each other.

      [2]
   3. (c)

      State the direction of the magnetic field at any point on these lines.

      [1]
2. 12

   A long straight wire carries a large current vertically. A plotting compass is moved around the wire at a fixed distance, and then the current is doubled. The current is finally switched off.

   1. (a)

      Describe the shape of the magnetic field around the wire.

      [1]
   2. (b)

      State what happens to the compass needle’s behaviour when the current is doubled.

      [2]
   3. (c)

      State what the compass shows when the current is switched off, and explain why.

      [2]
   4. (d)

      Name one practical device that combines this magnetic effect of a current with an iron core.

      [1]
3. 13

   A small generator has a rectangular coil rotating between the poles of a magnet. The coil is connected to the outside circuit by slip rings and brushes.

   1. (a)

      Explain why an e.m.f. is induced as the coil spins.

      [2]
   2. (b)

      Sketch or describe the shape of a graph of e.m.f. against time for two complete revolutions.

      [2]
   3. (c)

      State what happens to the graph if the coil spins at double the speed.

      [1]
4. 14

   A transformer has a primary coil of 1000 turns connected to a 230 V a.c. supply and a secondary coil of 50 turns feeding a low-voltage circuit. The secondary current is 4.0 A. Assume the transformer is 100% efficient.

   1. (a)

      Calculate the potential difference across the secondary coil.

      [2]
   2. (b)

      Calculate the primary current.

      [2]