Electromagnetic induction and generatorsIB MYP Physics: Subtopic test

1. 1
   A student in Lagos connects a coil of wire to a sensitive centre-zero voltmeter and moves a bar magnet into and out of the coil.

   (a)

   What does the voltmeter show when the magnet is held still inside the coil?

   [1 mark]

   • AZero
   • BA steady reading in one direction
   • CA reading that keeps changing direction
   • DThe largest reading it can show

   (b)

   Which change would give a larger induced e.m.f.?

   [1 mark]

   • AMoving the magnet more slowly
   • BUsing a weaker magnet
   • CUsing a coil with fewer turns
   • DMoving the magnet faster

   (c)

   Explain why the voltmeter needle swings the opposite way when the magnet is pulled out of the coil compared with when it is pushed in.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a school in Santiago, a bar magnet's north pole is pushed towards one end of a coil of wire. The coil is part of a complete circuit that includes a sensitive ammeter.

   (a)

   Which statement is Lenz's law?

   [1 mark]

   • AThe induced current always flows in the same direction
   • BThe induced current produces a magnetic field that helps the magnet to move
   • CThe induced current flows in a direction so that its magnetic field opposes the change that produced it
   • DThe induced current is always zero

   (b)

   What type of pole is produced at the end of the coil nearest the north pole of the magnet as it is pushed in?

   [1 mark]

   • AA south pole
   • BA north pole
   • CNo pole
   • DA pole that changes between north and south

   (c)

   Explain, in terms of energy, why it takes effort to push the magnet into the coil.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A simple a.c. generator in a school laboratory has a rectangular coil that is turned between the poles of a magnet. The ends of the coil are connected to slip rings and carbon brushes, and the output is displayed on an oscilloscope as a wave that repeats.

   (a)

   Explain how the generator produces an alternating e.m.f. when the coil is turned.

   [3 marks]

   (b)

   Describe the shape of the output wave, and state how its frequency and amplitude change if the coil is turned twice as fast. Give one other way of increasing the amplitude.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A science class in Manila investigates how to induce a voltage by moving a bar magnet through a coil connected to a sensitive voltmeter. A small island community nearby is deciding whether to install wind turbines with generators or to keep using a diesel generator.

   (a)

   The class hypothesises that the number of turns on the coil affects the induced e.m.f. 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 island should install wind turbines with generators instead of using the diesel generator.

   [6 marks]

   Total for question 4: 12 marks

End of questions