Current electricity

Conductors

Are materials through with electrical charges move freely

Insulators

Are materials in which electrical charges do not move freely

Semiconductors

Are a class of materials with conductivity in a range between that of a good and bad conductors.

Good conductors

Silver, gold , copper, aluminum, ghaphite

Semi-conductors

Silicon, germanium

Insulators

Glass, quartz, rubber, plastic, mica

Conventional current and electron flow

Current-

Is the rate of flow of charge

Current = I, charge= Q, time = t

I = Q/t

Q= It

The SI unit of charge

Coulomb, C

The SI unit of current

ampere, A

The current is 1 ampere when the rate of flow of charge is 1 coulomb per second through a point.

Since Q= It

1 C= 1A × 1s

1C = 1As

Conventional current

Is in the direction in which a POSITIVE charge would move if free to do so. It is the direction of the electric field.

Electron flow

is the flow of NEGATIVE charge and is therefore opposite to the direction of conventional flow.

Alternating current

ac is a current that repeatedly reverses direction with time.

Direct current

dc is a current that does not change direction with time.

Frequency, f

Is the number of complete cycles per second. Unit Hz

Period, T

Is the time taken for one complete cycle. Unit is “s”(second).