AP Physics III.D

Magnetic Fields

III.D1 − Magnetic Fields

The prized lodestone

Force of one magnet on another

Magnetic field as plainly demonstrated by iron filings and

compasses.

The direction of a magnetic field

The Force of a Magnetic Field on a Moving Charge

A magnetic field exerts a force on a charged particle when . . .

• The charge is moving

• The velocity of the moving charge has a component that is perpendicular to the direction of the field

Consider . . . 1) a magnetic field and the charge moving parallel or

antiparallel to the field

2) The charge moving at 90º to the direction of the field (time for

Right Hand Rule Number 1)

3) The charge moving between 0º and 180º to the direction of the

field

Note: for positive charges in a magnetic field use your right

hand. For negative charges in a magnetic field use your left hand.

Motion of a Charged Particle in a Magnetic Field

Work done on a charged particle moving through a electric and

magnetic fields

A for a handy formula which I never remember and is not a

“boxer” but one you can easily derive.

Ex. A particle with charge +q traveling with velocity v, enters a uniform magnetic field B, as shown below. Describe the particle’s motion.

B

+q

v

III.D.2 Force on a current carrying wire in a magnetic field

RHR-1 Again

Ex. A U-shaped wire of mass m is lowered into a magnetic field B that points in the plane of the page. What is the magnitude and direction of the current I that must pass through the wire if the net force on the wire is zero?

III.D.3 Magnetic fields produced by current-carrying wires

Electromagnetism – the linking of the motion of electric charges with

the creation of a magnetic field

Extraordinary Demo!

Right-Hand-Rule Number 2

+e

v0

I

Forces on parallel current carrying wires