Magnetic flux density (A-level only) Flashcards – AQA A-level Physics (7408)

What is the force magnitude on a straight wire perpendicular to a uniform magnetic field?

$F = BIl$, where $B$ is magnetic flux density, $I$ is current and $l$ is the length of wire in the field.

What is the direction of the force on a current-carrying wire relative to the current and magnetic field?

It is perpendicular to both the conventional current and the magnetic field.

How is magnetic flux density defined in terms of the force on a perpendicular current-carrying wire?

$B = \frac{F}{Il}$. It measures magnetic field strength in terms of the force on the wire.

What is one tesla, the SI unit of magnetic flux density?

The flux density that produces a force of 1 N on a 1 m wire carrying 1 A, perpendicular to the field.

In Fleming’s left-hand rule, what do the thumb, first finger and second finger indicate?

With the three digits mutually perpendicular:

• Thumb: force
• First finger: magnetic field
• Second finger: conventional current