Electromagnetism

A current-carrying wire in an external magnetic field has a force exerted upon it

Increase the current
Increase the number of wire coils
Increase the strength of the magnetic field

If a positively charged particle is moving across a magnetic field, then this is the same as a current in the direction of the proton's movement
If a negatively charged particle is moving across a magnetic field, then this is the same as a current in the opposite direction of the electron's movement

More current
More turns on the coil
Stronger magnetic field
A soft iron core in the coil

alternating current changes direction continuously
current in coil produces alternating magnetic field
this produces a force on the coil
this reverses the direction of the current, reversing the direction of the force
hence the cone vibrates and the cone vibrates air particles

the creation of a voltage (and maybe a current) in a wire that experiences a change in the magnetic field
happens when an electrical conductor (a coil of wire) moves through a magnetic field or the magnetic field through an electrical conductor changes (gets bigger, smaller or reverses)
if the direction of movement is reversed, then the induced voltage (or current) will be reversed

Increase strength of the magnet
Increase number of turns on the coil
Increase the speed of movement

using electromagnetic induction to generate electricity using energy from kinetic energy stores
in a power station, this energy is provided by the turbines

The commutator reverses the polarity of the magnets every half-turn so that the motor rotates in the same direction

Change the size of the voltage of an alternating current
Have two coils (a primary coil and a secondary coil) that are joined with an iron core

Increase the voltage
Have more turns on the secondary coil than on the primary coil

Decrease the voltage
Have more turns on the primary coil than on the secondary coil

Voltage produced by power stations is too low to be transmitted efficiently
Power = VI so the lower the voltage, the higher the current for a given amount of powerand current causes the wire to heat up
A step-up transformer is used to increase the voltage before it is transmitted
A step-down transformer is used at the end of the journey to reduce the voltage so it's more useful and safer to use