Magnetic Fields from Currents and Forces on Conductors

All flashcards

What does a current represent in a conductor?

An ordered movement of electric charge.

What is the magnetic-field pattern around a long, straight current-carrying wire?

Concentric circles centered on the wire; the field is stronger nearer the wire.

How does RHR-2 give the magnetic-field direction around a straight wire?

Point the right thumb along conventional current; curled fingers show the field direction.

What is the force on a straight wire in a uniform magnetic field?

$\vec F=I\vec\ell\times\vec B$, where $I$ is current and $\vec\ell$ points along it.

Can a closed current loop in a uniform magnetic field experience torque?

Yes. Its net force is zero, but a net torque may remain.

Quiz questions

1. Which expression gives the magnetic force on a straight wire segment in a uniform magnetic field?Answer: $\vec F=I\vec\ell\times\vec B$
2. At what angle between a straight wire's current and a magnetic field is the magnetic force greatest?Answer: $90^\circ$
3. What happens to the magnetic-force direction if either the current direction or the magnetic-field direction is reversed?Answer: The force direction reverses.
4. How is the net magnetic force on a curved wire in a magnetic field calculated?Answer: Integrate the vector force contributions along the wire.
5. What is the net magnetic force on a closed current loop in a uniform magnetic field?Answer: Zero, although the loop may still experience torque.