A current carrying coil placed in a uniform magnetic field experiences
Correct answer: B. a torque that tends to align its plane perpendicular to the field
- A. a net force that accelerates it across the field
- B. a torque that tends to align its plane perpendicular to the field
- C. neither force nor torque
- D. a force along the field lines
Explanation
The forces on opposite sides of the coil are equal and opposite, so they cancel and there is no net translational force, but because they act along different lines they form a couple that rotates the coil. The rotation continues until the plane of the coil is perpendicular to the field, at which point the torque is zero. A motor uses a commutator to reverse the current at that instant so rotation continues.
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About Magnetic Flux Density
Magnetic flux density measures the magnetic force acting on a current carrying conductor or moving charge in a magnetic field. Work includes the relations B equals F divided by IL and F equals qvB, the tesla as its SI unit, field direction and the distinction between flux density and magnetic flux.
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