Electromagnetic induction GapFill

Mains electricity is delivered by the national grid, which connects power stations to homes and businesses. At power stations, the potential difference of the electricity is increased using  step-down transformersramping solenoidsstep-up transformerssliding solenoids for transmission, and in homes the potential difference is decreased using  step-up transformersramping solenoidssliding solenoidsstep-down transformers for use by appliances.

A potential difference can be induced in a conductor by  a changing magnetic fielda constant magnetic fielda rotating iron corea constant electric field. If this potential difference is induced in a  coil of wiremagnetclosed circuitinsulator then a current will be induced. This is known as the  induction effectmotor effectsolenoid effectgenerator effect. This effect can be used in  a solenoidan alternatora dynamoa battery to produce an alternating current, and in  a dynamoa solenoida batteryan alternator to produce a direct current.
A transformer uses two coils around an iron core to increase or decrease a potential difference, often in the National Grid; an iron core is used because  it is a good electrical conductorit's easily magnetisedcurrents can change direction more quicklyit resists being magnetised, which means that the efficiency of the transformer increases. For a transformer,  Vp + Vs = Np + NsVp ÷ Vs = Ns ÷ NpVp ÷ Vs = Np × NsVp ÷ Vs = Np ÷ Ns, where V_p = potential difference across the primary coil, V_s = potential difference across the secondary coil, N_p = number of turns in the primary coil, and N_s = number of turns in the secondary coil.
If a transformer was 100 % efficient, then  Vp - Ip = Vs - IsVp ÷ Ip = Vs ÷ IsVp + Ip = Vs + IsVp × Ip = Vs × Is.