IB Physics SL D.3.4 Magnetic Force on a Charge

Practise calculating magnetic force on moving charges, using the right-hand rule with charge sign and explaining circular motion when velocity is perpendicular to a uniform field.

Exam points

calculate F = |q|vB sinθ and identify zero force for motion parallel to the field
use the right-hand rule for positive charge and reverse the force for negative charge
equate qvB to mv²/r to find orbit radius, momentum or charge-to-mass ratio

[Maximum number: 2]

In an experiment a student constructs the circuit shown in the diagram. The ammeter and the voltmeter are assumed to be ideal.

Figure for Question D.3.4—Magnetic force on charge question 1 — IB Physics SL

The diagram shows a cross-sectional view of the connecting wire in (c).

The wire which carries a current of 3.5 A into the page, is placed in a region of uniform magnetic field of flux density 0.25 T . The field is directed at right angles to the wire.

Determine the magnitude and direction of the magnetic force on one of the charge carriers in the wire.

$F=<q v B=1.6 \times 10^{-19} \times 2.0 \times 10^{-4} \times 0.25=>8.1 \times 10^{-24} \mathrm{~N}$

directed down OR south

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D.3.4—Magnetic force on charge question 1