Energy Transfer in Circuits


Unit: Coulomb, C

“The coulomb is the charge that flows past a point when a steady current of 1A passes for 1 second.”

Drift Velocity

The electrons in a current have an overall motion at low speed in a direction negative to the positive.

The three things that affect the drift velocity are:

• Current, I
• Charge carrier concentration, n: number of charge carrying electrons per unit volume
• Cross sectional area of material, A

For a metal:  I = n A e v    = electronic charge

For a non-metal:  I = n A q v    = ionic charge


Alternating Current and the Oscilloscope

Alternating and Direct Direct

A current from a battery is direct current, d.c., while mains electricity is alternating current, a.c.

a.c. changes direction, while d.c maintains the same direction even though the current value may vary.