Part 08 · Circuits and magnetism · Card 12 of 12
Force on a current-carrying wire
A wire carrying current I in a field B feels force F = B I L sin theta.
Last updated
Analogy
The principle of every electric motor.
Example
Wire in field
F = B I L= 0.2 x 4 x 0.5= 0.4 N
In practice
A 0.5 m wire carrying 4 A across a 0.2 T field feels 0.4 N.
Practice
Flashcards
- What is the force on a current-carrying wire?F = B I L sin theta.
Questions people ask
How does an electric motor use this force?
A coil of wire carrying current sits in a magnetic field. The force on the two sides points in opposite directions, so the coil turns. A commutator flips the current each half turn so the coil keeps rotating in the same direction.
How is this force related to the force on a single charge?
A wire holds many moving charges. Each feels q v B. Adding them up over the length L gives total force BIL, since current times length equals charge times velocity summed over the wire. So the wire formula is the single-charge formula for many charges.