Aim for FivePhysics 2

Translation between representations (TBR)

A square loop pulled through a magnetic field

  • Unit 12
  • 12 points
  • About 28 minutes

You can use a calculator on this question, just like on exam day.

A multipart problem about one situation shown in several ways. You draw a diagram, derive equations, sketch or draw graphs, and then explain whether your answers agree with each other or use them to predict what happens when the situation changes. On the exam: Question 2 of 4. New for May 2027: the free-response section is 95 minutes, down from 100, for all 4 questions (50% of your score), one of each type in this order. Calculator and equation sheet allowed. The CED suggests 25–30 minutes. This question type started in May 2025, so Physics 2 free-response questions from 2024 and earlier are built differently.

The question

A square loop of wire with sides of length 0.20 m and resistance 0.50 Ω lies in the plane of the page. A region of uniform magnetic field of magnitude 0.40 T, directed into the page, has straight, sharp left and right edges 0.50 m apart and extends far above and below the loop. An external force pulls the loop to the right at a constant speed of 2.0 m/s, with two of its sides parallel to the edges of the field region. At time t = 0, the loop's right side reaches the left edge of the field region.

Suggested time: 28 minutes

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Part (a)

2 points

Describe the direction of the induced current in the loop (clockwise, counterclockwise or none, as seen on the page) (i) while the loop is entering the field region, (ii) while it is completely inside it, and (iii) while it is leaving it. Justify your answers.

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Part (b)

3 points

While the loop is entering the field, (i) derive an expression for the magnitude of the external force needed to keep the loop moving at constant speed, in terms of the field B, the side length L, the speed v and the resistance R, and (ii) calculate the induced emf and the external force.

Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).

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Part (c)

3 points

Describe graphs of (i) the magnetic flux through the loop and (ii) the induced current in the loop as functions of time, from t = 0 to t = 0.40 s. Take counterclockwise current as positive. Include the axes with units, the times at which the graphs change, and the values.

Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).

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Part (d)

4 points

(i) Explain how your current graph is consistent with your flux graph. (ii) The loop is now pulled at 4.0 m/s instead. Predict how the external force needed while the loop enters the field, and the total energy dissipated in the loop while it enters, compare with their values at 2.0 m/s. Justify your predictions.

Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).

0 / 2,500 characters

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