11.5 Force and Torque on a Current Loop

Zero net force but real torque on a loop in a uniform field, the magnetic dipole moment that measures it, and the principle behind motors.

University Physics Volume 2, 11.5 Force and Torque on a Current Loop

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5 exercises

11.5 Exercise 1

Check Your Understanding

In what orientation would a magnetic dipole have to be to produce (a) a maximum torque in a magnetic field? (b) A maximum energy of the dipole?

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11.5 Exercise 2

(a) By how many percent is the torque of a motor decreased if its permanent magnets lose 5.0% of their strength? (b) How many percent would the current need to be increased to return the torque to original values?

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11.5 Exercise 4

Find the current through a loop needed to create a maximum torque of $9.0 \text{N} \cdot \text{m} .$ The loop has 50 square turns that are 15.0 cm on a side and is in a uniform 0.800-T magnetic field.

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11.5 Exercise 6

Since the equation for torque on a current-carrying loop is τ = NIAB sin θ, the units of N ⋅ m must equal units of A ⋅ m² T. Verify this.

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11.5 Exercise 8

A proton has a magnetic field due to its spin. The field is similar to that created by a circular current loop $0.65 \times 10^{−15} \text{m}$ in radius with a current of $1.05 \times 10^{4} \text{A} .$ Find the maximum torque on a proton in a 2.50-T field. (This is a significant torque on a small particle.)

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