Magnetic Effects of Electric Current

A current makes a magnetic field, a magnetic field pushes on a current, and household wiring uses fuses and earthing to keep that current safe.

Key ideas

Magnetic field lines go from the north pole to the south pole outside a magnet, never cross, and are closer where the field is stronger.
Around a straight wire the field lines are circles; the right-hand thumb rule gives their direction (thumb along the current).
The field is stronger nearer the wire and with a larger current.
A solenoid behaves like a bar magnet: the field inside is uniform, and the end where the current looks anticlockwise is the north pole.
A current in a magnetic field feels a force, greatest when the current is at right angles to the field; Fleming's left-hand rule gives its direction.
Homes get 220 V between the live (red) and neutral (black) wires; the earth wire (green) is for safety. Appliances are connected in parallel.
A fuse in the live wire melts if the current gets too large, from a short circuit or overloading.

Fleming's left-hand rule	forefinger: field; middle finger: current; thumb: force
Right-hand thumb rule	thumb: current; curled fingers: field
Current drawn by an appliance	I = P ÷ V
Appliances in parallel	total current = total power ÷ 220 V

Using the right hand for the force on a current (Fleming's rule uses the left hand).
Forgetting that an electron moving one way is a current in the opposite direction.
Putting the fuse in the neutral wire instead of the live wire.

An electron enters a magnetic field pointing west, moving towards the south. In which direction is it pushed?

Working: the electron's motion is a current in the opposite direction; then Fleming's left-hand rule

Answer: Vertically upwards