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AP · AP 2 · multiple choice

AP Physics 2: Algebra-Based · Question 4

AP Physics 2: Algebra-Based · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
routine
Marks
1
Topics
1
Answer
Complete
Straight current-carrying wire in a uniform magnetic field directed into the pageuniform magnetic field B = 0.40 T, into the pageI = 3.0 AL = 0.25 m
Figure 1A rectangular region of uniform magnetic field is shown by a grid of small crosses, marking a field of magnitude 0.40 T directed into the page. A straight wire lies horizontally across the region, in the plane of the page and therefore at right angles to the field, and an arrow drawn along the wire shows the conventional current of 3.0 A flowing to the right. A dimension line below the region, with projection lines dropped from each end of the wire, marks the length of wire lying in the field as L = 0.25 m. No force is shown.
multiple choice1 mark

A straight wire of length 0.25 m carries a current of 3.0 A at right angles to a uniform magnetic field of magnitude 0.40 T. What is the magnitude of the magnetic force on the wire?

  1. A

    0.030 N

  2. B

    0.30 N

  3. C

    3.0 N

  4. D

    4.8 N

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Answer overviewCorrect answer: B — 0.30 N
01

Answer and reasoning

1 mark
How to approach it

Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.

  1. 1

    The correct choice is B: 0.30 N

  2. 2

    F = BIL = 0.40 × 3.0 × 0.25 = 0.30 N. A and C are decimal-place slips of the kind that survive on an exam where no working is seen, which is why the item is worth doing carefully rather than quickly. D multiplies all three numbers and then adds the field again.

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