1. 1
   A student holds a plotting compass at several points around a long, straight, current-carrying wire, noting the direction the compass needle points, in order to investigate the magnetic field produced by the current.

   (a)

   What is the overall shape of the magnetic field pattern around a straight current-carrying wire?

   [1 mark]

   • AA series of concentric circles centred on the wire
   • BStraight lines running parallel to the wire
   • CStraight lines pointing directly away from the wire in all directions
   • DNo magnetic field is produced around a straight wire

   (b)

   The student then reverses the direction of the current in the wire and repeats the test with the compass at the same points. What happens to the direction shown by the compass needle at each point?

   [1 mark]

   • AThe compass needle always points directly along the wire, regardless of current direction
   • BThe compass needle points in exactly the same direction as before
   • CThe compass needle stops responding to the field altogether
   • DThe compass needle points in the opposite direction to before

   (c)

   State how the strength of the magnetic field around the straight wire varies with distance from the wire, and state one way the student could increase the strength of the field at a fixed distance from the wire.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An electrical engineer builds a solenoid by winding many turns of insulated wire into a long coil, and investigates how its magnetic field pattern and strength compare with those of a single straight current-carrying wire.

   (a)

   Compared with the field around a single straight wire, how does the field pattern produced by a solenoid, away from its ends, compare?

   [1 mark]

   • AThe solenoid produces no magnetic field at all, unlike a straight wire
   • BThe solenoid produces exactly the same simple circular field pattern as a straight wire
   • CInside the solenoid, the field is strong and roughly uniform, similar in pattern to that of a bar magnet, unlike the simple circular pattern around a straight wire
   • DThe solenoid's field exists only outside the coil, with no field inside it

   (b)

   The engineer wants to increase the strength of the magnetic field produced by the solenoid without changing the current. Which of these changes would achieve this?

   [1 mark]

   • ADecreasing the number of turns of wire on the solenoid
   • BIncreasing the number of turns of wire on the solenoid
   • CRemoving the insulation from the wire
   • DWinding the wire in the opposite direction only

   (c)

   Describe how the engineer could use iron filings or a plotting compass to identify the pattern of the magnetic field produced both inside and around the outside of the solenoid.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A doorbell mechanism uses a small electromagnet, made from a solenoid wound around an iron core, to attract a metal striker towards a bell each time the doorbell button completes the circuit, and a loudspeaker in the same house uses a related magnetic effect to produce sound.

   (a)

   A doorbell mechanism uses a small electromagnet (a solenoid with an iron core) to attract a metal striker towards a bell each time the doorbell button completes the circuit. Explain how pressing the doorbell button causes the striker to be attracted, referring to the magnetic effect of the current in the solenoid.

   [3 marks]

   (b)

   In the same house, a loudspeaker uses a coil of wire (carrying a varying current from an amplifier) placed within the field of a permanent magnet, attached to a paper cone. Explain, using the magnetic effect of a current, how varying the current in the loudspeaker's coil causes the cone to move and produce sound, and explain what would happen if the direction of the current in the coil were reversed.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In the early days of long-distance communication, engineers built electric telegraph receivers using an electromagnet made from a solenoid wound around a soft iron core, which attracted a small lever whenever a pulse of current was sent along the telegraph line.

   (a)

   Explain, using the pattern and strength of the magnetic field produced by a current-carrying solenoid, why a solenoid with an iron core was a much more effective choice for this device than a single straight wire carrying the same current, and explain how the strength of the field could be increased if a stronger attraction on the lever was needed.

   [6 marks]

   (b)

   An engineer maintaining an old telegraph line notices that reversing the two wires connecting the battery to the solenoid at the sending station still causes the receiving station's lever to be attracted just as strongly as before, but a colleague at another site reports that reversing the wires at their station instead makes their receiver's field noticeably weaker when combined with a second nearby solenoid wound in a fixed direction. Explain why simply reversing the current direction through a single solenoid does not change the strength of the attraction it produces, but explain how the relative winding direction and current direction of two nearby solenoids could combine to increase or decrease the total field strength where they overlap.

   [6 marks]

   Total for question 4: 12 marks

End of questions