Electrical energy and voltage

Each coulomb of electricity that flows from a battery has some energy. The voltage of the battery tells us just how much energy. So if one coulomb of electric charge flows from a 240 V source, it will have more energy than one from a 12 V source.
We can compare voltage with gravitational (potential) energy in the pictures below.



The potential difference (voltage) is measured between two points on the circuit with a voltmeter. It is really measuring the loss of energy of the electricity between one point and the other.

This is shown by the diagrams in Figure 2. The reading of V₁ in the first circuit shows how much energy is lost in the bulb - it is turned into heat and light. The reading of V₂ will be 0, as almost no energy is lost in the connecting wires.

In the second circuit the battery is supplying energy to two bulbs. If the bulbs are identical the energy lost in one will be the same as the energy lost in the other.
Using the figures in the diagram there will be a 3 V drop across each bulb.

In the third circuit one bulb is much more powerful than the other, there is much more energy used in it and so the voltage drop across it is large compared with the other bulb.