The motor effect and electric motorsIB MYP Physics: Subtopic test

1. 1
   In a demonstration in Istanbul, a copper rod rests on two horizontal metal rails between the poles of a strong horseshoe magnet. When a current from a d.c. supply is passed through the rod, the rod rolls along the rails.

   (a)

   What name is given to the effect that makes the rod move?

   [1 mark]

   • AElectromagnetic induction
   • BElectrolysis
   • CMagnetic induction
   • DThe motor effect

   (b)

   The current through the rod is reversed. What happens to the force on the rod?

   [1 mark]

   • AIt stays the same
   • BIt acts in the opposite direction
   • CIt becomes zero
   • DIt doubles in size

   (c)

   State two changes that would increase the force on the rod.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A straight horizontal wire passes at right angles between the poles of a large magnet. The north pole is on the left and the south pole is on the right, so the magnetic field points to the right. The conventional current in the wire flows away from the observer.

   (a)

   In which direction is the force on the wire?

   [1 mark]

   • AUpwards
   • BTo the left
   • CDownwards
   • DTo the right

   (b)

   In Fleming's left-hand rule, which finger or digit points in the direction of the current?

   [1 mark]

   • AThe second finger
   • BThe thumb
   • CThe first finger
   • DThe little finger

   (c)

   The poles of the magnet are swapped and the current is also reversed. State the direction of the force on the wire and explain your answer.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students in Nairobi build a model d.c. motor. A rectangular coil of wire is placed between two magnets and connected to a battery through a split-ring commutator and carbon brushes.

   (a)

   Explain why the coil starts to turn when the battery is connected.

   [3 marks]

   (b)

   Explain the purpose of the split-ring commutator, and state two ways of making the motor turn faster.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technology team in Jakarta builds model buggies driven by small d.c. motors and investigates how the voltage of the supply affects the speed of a buggy. A delivery company in the same city is also deciding whether to replace its diesel vans with electric vans driven by motors.

   (a)

   The team hypothesises that the voltage of the supply affects the speed of the buggy. State a testable hypothesis with a scientific reason, identify the independent, dependent and one control variable, and outline a safe method.

   [6 marks]

   (b)

   Discuss and evaluate whether the delivery company should replace its diesel vans with electric vans.

   [6 marks]

   Total for question 4: 12 marks

End of questions