| Date | May 2015 | Marks available | 3 | Reference code | 15M.2.HL.TZ2.5 |
| Level | Higher level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Calculate | Question number | 5 | Adapted from | N/A |
Question
This question is about changing magnetic fields.
A single-turn conducting square coil is released and falls vertically from rest. At the instant it is released, the coil is at the boundary of a region of a uniform horizontal magnetic field directed into the plane of the paper as shown. The ends of the coil are not joined together.
Each side of the coil is 0.050 m long. The dimensions of the magnetic field region are greater than that of the coil. The magnetic field strength is 25 mT.
Calculate the electromotive force (emf) induced in the coil at the instant just before the whole of the coil enters the magnetic field.
Suggest why the time taken for the whole of the coil to enter the magnetic field increases if the coil is a continuous loop.
Markscheme
speed as the whole of the coil enters the field \( = \sqrt {2 \times 9.81 \times 0.05} \) (=0.99 ms-1);
\(\left( {\varepsilon = \left( - \right)\frac{{\Delta \varphi }}{{\Delta t}}} \right) = 0.05 \times 0.99 \times 25 \times {10^{ - 3}}\);
1.23(mV) or 1.24(mV0; (allow use of g=10 to give 1.25(mV))
Award [3] for a bald correct answer.
Use of factor 4 appears if candidate thinks all sides of coil contribute to emf [2 max].
current (induced) in the coil;
this will act so as to oppose the movement / reference to Lenz’s law;
force will be upwards/resistive/counteracts the effect of gravitational force;
