1. 1
   A small DC motor is used to spin the blades of an electric desk fan. The motor contains a rectangular coil of wire that rotates between the poles of a permanent magnet, and a direct current from a battery is supplied to the coil through carbon brushes pressed against a split-ring commutator.

   (a)

   Which pair of components allows the current in the coil to reverse direction every half turn, keeping the coil turning in the same direction?

   [1 mark]

   • AThe split-ring commutator and the carbon brushes
   • BThe permanent magnet and the coil
   • CThe battery and the connecting wires
   • DThe fan blades and the drive shaft

   (b)

   The fan has a low-speed and a high-speed setting. On the high-speed setting, a larger current is supplied to the coil. What effect does increasing the current have on the turning effect of the motor?

   [1 mark]

   • AThe turning effect decreases
   • BThe turning effect increases
   • CThe turning effect stays the same
   • DThe coil stops turning completely

   (c)

   State two changes, other than increasing the current, that could be made to the fan motor to increase its turning effect.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer builds a simple demonstration DC motor on a workbench. A rectangular coil is placed between the poles of a horseshoe magnet, with the N pole on the left and the S pole on the right, and a direct current is passed through the coil from a battery.

   (a)

   An engineer builds a simple DC motor on a workbench to demonstrate to students. A rectangular coil is placed between the poles of a horseshoe magnet, with the N pole on the left and the S pole on the right. Current flows up one side of the coil and down the other. What is the name of the rule used to predict the direction of the force on each side of the coil?

   [1 mark]

   • AThe right-hand grip rule
   • BOhm's law
   • CNewton's third law
   • DFleming's left-hand rule

   (b)

   The engineer reverses the direction of the current flowing through the coil, while keeping the magnet's poles the same. What happens to the direction of rotation of the coil?

   [1 mark]

   • AThe coil stops rotating and does not restart
   • BThe direction of rotation stays the same
   • CThe direction of rotation reverses
   • DThe coil rotates twice as fast in the same direction

   (c)

   The engineer then reverses the poles of the magnet back to their original positions but instead reverses the current a second time, returning it to its original direction. Explain what happens to the direction of rotation of the coil compared with the very first test, and give a reason for your answer.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A factory uses a large DC motor to drive a conveyor belt that carries packages between two floors. The motor coil rotates continuously in the magnetic field produced by two fixed permanent magnets.

   (a)

   Explain, with reference to the split-ring commutator, why the coil is able to rotate continuously in one direction rather than oscillating back and forth.

   [3 marks]

   (b)

   The factory manager wants to increase the speed of the conveyor belt without changing the coil or the current supplied. Suggest one modification to the motor's magnet system that would achieve this, and explain, in terms of the force on the coil, why your suggestion works. State one practical drawback of your suggestion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital uses an electric wheelchair powered by a DC motor connected to a rechargeable battery, allowing patients with limited mobility to move independently around the wards.

   (a)

   Describe, in detail, the construction and operation of a simple DC motor of the type used in the wheelchair, including the roles of the coil, the magnetic field, the split-ring commutator and the carbon brushes, and explain how a continuous turning effect in one direction is produced.

   [6 marks]

   (b)

   The wheelchair's motor sometimes needs more turning effect when climbing a ramp. Explain three separate ways the motor's turning effect could be increased, describe how each change affects the force or torque produced, and discuss one possible disadvantage for each way of achieving this in a wheelchair.

   [6 marks]

   Total for question 4: 12 marks

End of questions