MYP Physics Electric and Magnetic Fields Notes

How Can Electricity Create Magnetism?

1. Physicists often prefer a small number of universal laws rather than many separate rules for specific situations.
2. A major success of this approach was James Clerk Maxwell's theory of electromagnetism, which showed that electricity and magnetism are deeply linked.

The Magnetic Effect of an Electric Current

1. When an electric current flows through a wire, it creates a magnetic field around the wire.
2. This magnetic field exists only while the current is flowing.
3. If the current stops, the magnetic field disappears immediately.
4. This shows that electricity and magnetism are closely linked.

Shape of the Magnetic Field Around a Straight Wire

1. The magnetic field around a straight current-carrying wire forms concentric circles.
2. These circles are centred on the wire.
3. The magnetic field gets weaker as the distance from the wire increases.
4. There are no north or south poles around a straight wire.

The Right-Hand Grip Rule Gives The Field Direction

1. To find the direction of the magnetic field around a straight current-carrying wire:
   1. Point your right thumb in the direction of the conventional current $I$.
   2. Your curled fingers show the direction of the magnetic field $\mathbf{B}$.
2. If the current is towards you (out of the page), the field circles anticlockwise.