Magnetism and electromagnetism - how does things work

HOW DOES A LOUDSPEAKER WORK

• The moving-coil loudspeaker uses the motor effect to change electrical energy into sound energy.
• A source emits signals which are fed into the coil of the speaker as current (this current continually changes in size and direction.)
• The overlapping fields of the coil and the magnet therefore create rapidly varying forces on the wires of the coil.
• This causes the speaker cone to vibrate.
• These vibrations create the sound waves we hear.

THE ELECTRIC BELL

• When the bell push is pressed the circuit is complete and current flows.
• The soft iron core of the electromagnetic becomes magnetised and attracts the iron armature.
• When the armature moves the hammer strikes the bell and at the same time a gap is created at the contact screw. The circuit is now incomplete, current stops flowing.
• The electromagnet is now turned off so the spring's armature returns to its original position.
• The circuit is complete again and the process begins again.

THE RELAY SWITCH

• -Uses a small current in 1 circuit to turn on a second circuit that may be carrying a much larger current.
• When switch S is closed a small current flows around the circuit on the left.
• The current passes through coil C and the soft iron core becomes magnetised as a result and attracts the iron armature.
• The armature is pivoted at X, this causes its lower end Y to push the contacts of the second circuit together.
• The circuit is complete and larger current flows. User would not come into contact with a potentially more dangerous current.

CIRCUIT BREAKER

• When the current is too high the electromagnet becomes strong enough to pull the iron catch out of position so that the contacts open and the circuit.
• Once the problem in the circuit has been corrected the catch is repositioned by pressing the reset button.