Matter & Interactions 2nd ed. Practice Problems
Aaron Titus | High Point University
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2k80002     Torque on a coil     2k80002
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A coil of 20 turns of wire has a radius 0.5 cm and is connected to a power supply so that 0.4 A flows through the coil. At , the coil is at rest, current flows into the page at the top of the coil, and the plane of the coil makes an angle of with respect to a magnetic field of 0.5 T.

Figure: A coil in a uniform magnetic field.

  1. At the instant shown (t=0), what is the torque on the coil?
  2. In what direction will the loop rotate if it is released from rest?
  3. What is the magnetic potential energy of the loop at t=0?
  4. If the system is frictionless, what will be the kinetic energy of the coil when it reaches its equilibrium orientation?
  5. Describe the motion of the coil, even after a long time, if the system is frictionless.


2k80001     Torque on a beam     2k80001
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A 1.5-m beam has a 1-kg object hanging from its end. The beam is held in equilibrium at an angle of with respect to the horizontal, as shown below. To hold the beam in equilibrium, you grasp a handlebar of radius 2 cm at the bottom of the beam and exert a tangential force on the handlebar.

Figure: A beam in equilibrium.

  1. If the mass of the beam is negligible, what is the torque by the object on the beam, about the axis of rotation O?
  2. What magnitude force must you apply tangentially at the handlebar in order to keep the beam in equilibrium?


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