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Learning Introductory Physics with Activities

Paul J. Emigh, Rebecka Tumblin, Kathryn Hadley, Danielle Skinner

Section 28.5 Current Loops

Subsubsection Activities

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Activity 28.5.1. Magnetic Dipoles.

For each of the current loops shown below:
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Three current loops, from top to bottom: clockwise when viewed from above, counterclockwise when viewed from above, clockwise when viewed from the right.
Figure 28.5.1. Three current loops.
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(a)

Use the right-hand rule to determine the magnetic dipole moment of the loop.
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(b)

Sketch and label a small bar magnet that would have the same magnetic dipole moment as the loop.
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Activity 28.5.2. Dipole Energy.

Rank the configurations below from smallest to largest potential energy. Check that your ranking makes sense by figuring out what the magnet is likely to do in each situation.
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Four bar magnets, each above a loop carrying clockwise current when viewed from above. From left to right: Case A has the north end of the bar magnet down, Case B has the south end down, case C has the north end to the left, case D has the north end to the right.
Figure 28.5.2. Four magnet configuration.
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Activity 28.5.3. Flux Loops.

A square loop (side length \(s\)) in the plane of the screen is in a region of magnetic field. Find the magnetic flux through the loop if:
  1. The magnetic field is a uniform \(B_o\) and points into the screen.
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  2. The magnetic field is a uniform \(B_o\) and points to the right.
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  3. The magnetic field points into the screen and increases linearly from \(0\) along the left edge to \(B_o\) along the right edge.
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Activity 28.5.4. The Pickup Coil.

Run this simulation. Go to the Pickup Coil tab.
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(a)

Play with the simulation for a few minutes. Record a list of observations.
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(b)

How many different kinds of changes can you make that will cause the light bulb to light up?
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(c)

Consider the statement: “While the magnetic flux through the loop changes, there is current induced in the loop.” What evidence is there to support this statement? Can you find any evidence to refute the statement? Can you find any evidence that suggests the statement is incomplete?
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(d)

Identify what properties the induced current in the loop depends on. Justify your answers with evidence from the simulation.
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Activity 28.5.5. Force on a Circuit.

The square circuit below is in a region with a uniform magnetic field.
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(a)

Determine the current through each side of the square circuit.
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(b)

Determine the direction of the magnetic force on each side of the square circuit.
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(c)

Does the magnetic field exert a net nonzero magnetic force on the loop? If so, what direction is the net force?
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(d)

Does the magnetic field exert a net nonzero magnetic torque on the loop? If so, what direction would you expect the loop to rotate (starting from rest)?
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