Electrical energy and power

Electrical energy

The potential difference (PD) measured in volts gives information on the power supplied to the current by the cell.

If the PD is one volt then the cell provides each coulomb with one joule of energy so:

Measuring PD (voltage) of lamp

Energy = charge x PD

and since charge = current x time then

energy = current x time x PD

in symbols

E = ItV

Where E is in joules, I in amps, t in seconds and V in volts

The voltmeter on the right around the lamp  gives information on the power provided by the current to the lamp. If the PD is one volt then each coulomb provides the lamp with one joule of energy so:

The equations are exactly the same, so again: Energy = charge x PD and since charge = current x time then

energy = current x time x PD in symbols E = ItV

Electrical Power

Since power = energy transferred/time

Then electrical power = ItV/t  The value of t cancels out, so

Power = IV power is measures in watts which is the same as joules per second

In this case the two values of PD are the same since the only component in the circuit apart from the cell is the lamp. Almost all the energy leaving the cell is transferred to the lamp since only a tiny amount of energy is used to drive the current through the thick copper wires. Some energy will however be changed to heat inside the cell- see internal resistance and EMF.