Observation

(a ) Principle of operation in starter motor
      The operation of a starter motor is based on the principle of electromagnetism.                                                                 When current flows through a conductor placed in magnetic field, a force is created acting on the conductor relative to the field. The magnitude of this force is proportional to the field strength, length of the conductor in the field and the current flowing. The effect of the electromagnetic force causes the starter motor armature to turn.                                                                                                                        
(b)Function of parts of a starter motor
(i) Solenoid –  It closes a pair of heavy contacts to engage the starter motor
                     - It pushes the plunger to engage the pinion to the flywheel.                 
(ii) Carbon brushes – conduct current to the commutator and thus generate a magnetic
field that mechanically turns the armature.                                                                     
(iii) Switch – energizes/activates the solenoid.                                                              
(iv) Pinion – connects the flywheel gear and thus cranks the engine.                            
 (c) (i) The spring at the end of the motor shaft.                                                            
(ii) Reason why a copper alloy is used as a starter brush

• It has high electrical conductivity.
• To minimize copper loss.
• To reduce wear of the brushes
• It has a high thermal conductivity

The performance of candidates in this question was average.