1. 1
   A student sets up a long straight vertical wire passing through a horizontal sheet of card. A direct current flows upwards through the wire. The student places several plotting compasses on the card at different distances from the wire and marks the direction each compass needle points, then repeats the investigation with a larger current.

   (a)

   A student holds a plotting compass just above a long straight vertical wire carrying a direct current. The current flows upwards through the wire. Which shape best describes the magnetic field produced around the wire?

   [1 mark]

   • AConcentric circles centred on the wire, in a plane perpendicular to the wire
   • BStraight field lines running parallel to the wire
   • CField lines radiating outward from the wire like spokes on a wheel
   • DA uniform field pointing in one direction everywhere around the wire

   (b)

   The student increases the size of the direct current in the wire but keeps the compasses at the same distances from the wire. What happens to the strength of the magnetic field at each compass position?

   [1 mark]

   • AIt reverses direction but stays the same strength
   • BIt decreases
   • CIt stays the same
   • DIt increases

   (c)

   The student notices that the compasses placed further from the wire show smaller needle deflections than those placed close to the wire, even when the current is unchanged. Explain this observation in terms of the magnetic field produced by the wire.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A straight copper wire is threaded between the poles of a strong horseshoe magnet so that the wire is perpendicular to the magnetic field lines running from the north pole to the south pole. The wire is connected to a direct current supply and a variable resistor, allowing the size of the current in the wire to be changed. When the circuit is switched on, the wire is observed to jump upwards out of the magnetic field.

   (a)

   A straight copper wire is placed between the poles of a strong horseshoe magnet, at right angles to the magnetic field, and carries a direct current. Which term describes the force produced on the wire?

   [1 mark]

   • AElectrostatic attraction
   • BElectromagnetic induction
   • CThe motor effect
   • DMutual induction

   (b)

   The student uses Fleming's left-hand rule to check the direction of the force on the wire. Which statement correctly describes how the rule is applied?

   [1 mark]

   • AThe thumb points along the magnetic field, the first finger points along the current, and the second finger gives the direction of the force
   • BThe First finger points along the magnetic Field (north to south), the seCond finger points along the Current, and the thuMb gives the direction of the force (Motion)
   • CAll three digits are pointed in the same direction as the current
   • DThe First finger points along the Current, the seCond finger points along the Field, and the thuMb gives the force, using the right hand

   (c)

   The wire has a length of 0.05 m within the magnetic field, and the magnetic flux density of the field is 0.4 T. Calculate the force on the wire when the current is 3 A. Give your answer to 2 significant figures and include the unit.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician builds a simple electric motor by mounting a rectangular coil of wire on an axle between the poles of a permanent magnet, so the coil can spin freely. The coil is connected to a direct current supply via a split-ring commutator and carbon brushes, which allow the coil to keep rotating continuously in the same direction rather than oscillating back and forth.

   (a)

   A technician replaces the straight wire between the magnet's poles with a rectangular coil of wire, positioned so that the two long sides of the coil each lie perpendicular to the magnetic field but on opposite sides of the field, carrying current in opposite directions along the length of each side. Explain why this arrangement produces a turning effect (a couple) on the coil rather than the coil simply moving upwards or downwards as a whole.

   [3 marks]

   (b)

   Explain the role of the split-ring commutator in allowing the coil to rotate continuously in the same direction, rather than reversing direction every half turn.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineer is comparing two possible designs for the coil of a small electric motor intended for a toy car. Design 1 uses a coil with a single loop of wire. Design 2 uses a coil with many turns of wire wound around the same axle, carrying the same current as Design 1, in the same magnetic field.

   (a)

   Describe and explain, in as much detail as possible, why Design 2 produces a greater turning effect on the axle than Design 1, referring to the force on each side of the coil and how the individual turns combine.

   [6 marks]

   (b)

   The engineer then investigates how the turning effect changes if a stronger permanent magnet is used, or if the current in the coil is increased, while keeping everything else in each design the same. Evaluate how each of these two changes (using a stronger magnet, and increasing the current) would affect the force on each side of the coil and the resulting turning effect of the motor, and explain any practical limitation the engineer would need to consider when increasing the current.

   [6 marks]

   Total for question 4: 12 marks

End of questions