1. 1
   A student places a straight current-carrying wire between the poles of a horseshoe magnet, perpendicular to the magnetic field, to investigate the force produced on a current-carrying conductor in a magnetic field.

   (a)

   A student places a straight wire between the poles of a horseshoe magnet, perpendicular to the magnetic field, and passes a current through it. The wire is observed to jump sideways. What causes this movement of the wire?

   [1 mark]

   • AA force acts on the current-carrying wire because it is in a magnetic field
   • BThe wire becomes permanently magnetised and is repelled by the magnet
   • CThe wire heats up and expands, pushing itself out of the field
   • DThe magnet's field induces a current that flows out of the wire into the air

   (b)

   The student then reverses the direction of the current in the wire, keeping the magnet's field direction the same. What happens to the direction of the force on the wire?

   [1 mark]

   • AThe wire's direction of force cannot be predicted
   • BThe force stays in exactly the same direction as before
   • CThe force disappears completely
   • DThe force reverses direction

   (c)

   State what would happen to the force on the wire if, instead of reversing the current, the student reversed the direction of the magnetic field instead (keeping the current direction the same), and state what would happen if both the current direction and the field direction were reversed together.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A cordless power drill contains an electric motor with a coil that rotates continuously between the poles of a permanent magnet, driven by direct current from a rechargeable battery.

   (a)

   What additional component allows the motor's coil to keep rotating continuously in the same direction, rather than oscillating back and forth?

   [1 mark]

   • AA fixed diode connected across the coil
   • BA step-down transformer
   • CA split-ring commutator, together with brushes
   • DA second, identical permanent magnet

   (b)

   The drill's motor spins faster and with a greater turning effect when the battery is fully charged, delivering a larger current. Why does increasing the current increase the turning effect (torque) on the coil?

   [1 mark]

   • AA larger current decreases the strength of the permanent magnet's field
   • BA larger current increases the force on each side of the coil in the magnetic field, increasing the overall turning effect
   • CA larger current has no effect on the turning effect of the coil
   • DA larger current reduces the number of turns on the coil

   (c)

   State two further ways, besides increasing the current, that the turning effect on the drill motor's coil could be increased.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In an old television's cathode ray tube, a narrow beam of electrons travels through a region containing a magnetic field, directed at right angles to the beam's direction of travel, in order to steer the beam across the screen.

   (a)

   Explain what happens to the direction of travel of the electron beam as it passes through this magnetic field, referring to the force produced on moving charged particles in a magnetic field.

   [3 marks]

   (b)

   Explain what would happen differently to the direction of deflection of the electron beam if the direction of the magnetic field in the tube were reversed, and explain what would happen if a beam of positively charged particles, rather than electrons, were sent through the same unchanged magnetic field.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In the early 19th century, scientists first demonstrated that a current-carrying wire experiences a force when placed in a magnetic field, an effect that eventually led to the invention of the electric motor, using a rotating coil, magnets, and a split-ring commutator.

   (a)

   Explain, using the relative directions of current, field and force, and the factors affecting the turning effect on a current-carrying coil, how winding the wire into a coil and placing it between magnetic poles produces a continuous turning effect, and explain why a simple coil alone would not keep rotating in one direction without an additional component.

   [6 marks]

   (b)

   An inventor building an early prototype motor notices that if the split-ring commutator is fitted incorrectly, so that it reverses the coil's connections at the wrong point in each rotation rather than exactly every half turn, the motor runs unevenly and with a reduced turning effect compared with a correctly fitted commutator. Explain, using the relative directions of current, field and force, and the factors affecting the size of the turning effect, why the timing of the commutator's reversal matters for producing a smooth, maximum, continuous turning effect.

   [6 marks]

   Total for question 4: 12 marks

End of questions