Magnetism The shadow of electricity. Magnetic Force Magnets apply forces to each other. Opposite...

Magnetism

The shadow of electricity

Magnetic Force

Magnets apply forces to each other.

Opposite poles attract, like poles repel.

CPS Question

The magnitude of the force between magnetic poles

A. is the same at all distances.

B. becomes stronger as the poles come closer.

C. becomes weaker as the poles come closer.

Magnetic Field Lines

Field lines point from North to South pole.

Conventions as with electric field lines.

strong field where lines are close together

direction is direction of force on a north pole

Group Work

1. What happens to a dipole magnet in a uniform magnetic field?

B

N

S

Naming the polesN = north-seeking

Earth’s north pole is a south pole!

Current Creates Magnetism

An electric current creates a magnetic field.

Look, Ma! No poles!

Vector Direction Conventions

Up Down

In Out

RightLeft

Poll Question

If a wire in front of you carries a current from left to right, what is the direction of the resulting magnetic field where you are?

I

A. B. C.

D. E. F.

Board Work

An electric current creates a magnetic field whose lines circle right-handed around it. Draw lines for the magnetic field created by a ring of current.

I

Magnetic Field of Current Ring

Source: Griffith, The Physics of Everyday Phenomena

N

S

dipole field

Solenoid Magnetic Field

Source: Griffith, The Physics of Everyday Phenomena

N S

Electrons are Magnets!

spin

Electrons are Magnets!

current

Electrons are Magnets!

magnetic field

Electrons are Magnets!

N

S

magnetic dipole

Types of Magnets

• Electromagnets– currents travel through conducting coils

• Permanent Magnets– materials whose electrons have aligned spins

or orbits

Moving charges create the fields!