| Date | May 2015 | Marks available | 3 | Reference code | 15M.2.HL.TZ1.8 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 8 | Adapted from | N/A |
Question
This question is in two parts. Part 1 is about the electrical and magnetic characteristics of a loudspeaker. Part 2 is about vibrations and waves.
Part 1 Electrical and magnetic characteristics of a loudspeaker
The diagram shows the main features of a loudspeaker L. A current-carrying coil is positioned within the magnetic field provided by a permanent magnet. The diagram also shows the directions of the magnetic field and of the current in the coil at a particular instant. The dust cap D prevents dust from blocking the gap between the cardboard tube and the south pole of the magnet.
The coil consists of 150 turns, each of average diameter 2.5 cm. The magnetic field of the permanent magnet has strength 0.40 mT. The peak current in the coil is 0.45 mA.
Identify, on the diagram, the direction of the force on the coil with the current directions shown.
Calculate the maximum magnetic force acting on the coil.
Explain, with reference to electromagnetic induction, the effect of the motion of the coil on the current.
Markscheme
force in correct location on diagram, ie arrow on coil;
force direction to the right;
Award [1 max] if any other forces drawn.
\(L = \left( {2\pi rN} \right) = 2 \times \pi \times 1.25 \times {10^{ - 2}} \times 150 = \left( {11.8} \right){\rm{m}}\);
\(F = \left( {{\rm{BIL}}} \right) = 0.40 \times {10^{ - 3}} \times 0.45 \times {10^{ - 3}} \times 11.8\);
\( = 2.1 \times {10^{ - 6}}{\rm{N / 2.1}}\mu {\rm{N}}\)
(as the coil moves the) conductor cuts the magnetic field / there is a change in flux linkage;
induces an emf across the coil / a current through the coil;
opposes the driving potential difference;
reduces the (net) current;
