IB Physics SL D.3.5 Force on current conductor

Practise calculating and predicting the magnetic force on current-carrying conductors, rods and circuit sections in uniform fields.

Exam points

calculate force or current from F = BIL when a wire or rod is at right angles to a uniform magnetic field
use a circuit-and-field diagram to determine the force direction on a rod or wire and predict the resulting motion
apply changes in current or force data to determine B from the gradient-like relation between F and I for fixed L

[Maximum number: 3]

The long straight conductor is formed into a coil consisting of two separate turns, X and Y . The coil hangs with its axis vertical.

Figure for Question D.3.5—Force on current conductor question 1 — IB Physics SL

Assume that the turns of the coil each behave as a long straight conductor.

The current in the coil is 15 A and the circumference of one turn is 0.48 m . In order to restore X and Y to their original separation, a mass of $2.8 \times 10^{-4} \mathrm{~kg}$ is suspended from turn Y . Estimate the magnetic field strength at X due to Y .

A3. This question is about radioactivity.

Caesium-137 ( ${ }_{55}^{137} \mathrm{Cs}$ ) is a radioactive waste product with a half-life of 30 years that is formed during the fission of uranium. Caesium-137 decays by the emission of a beta-minus $\left(\beta^{-}\right)$ particle to form a nuclide of barium (Ba).

$F=\left(0.280 \times 10^{-3} \times 9.81=\right) 2.75 \times 10^{-3} \mathrm{~N}$ ;
$B=\frac{F}{I l}$ or correct substitution $2.75 \times 10^{-3}=B \times(15) \times 0.48$ ;
$B=\left(\frac{2.75 \times 10^{-3}}{15 \times 0.48}=\right) 3.8 \times 10^{-4} \mathrm{~T} ;$

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D.3.5—Force on current conductor question 1