Potential difference
Posted in Physics, SensingElectrons pick up energy at in the cell of a battery and deliver it to the components of the circuit. When electrons return to the cell they have given up all the energy they gained. Voltage is defined as the energy per unit charge or:
Where V is the voltage in volts, E is the energy in joules and Q is the charge in coulombs
Potential difference (p.d.) is the difference in electrical potential energy - voltage - between any two points in a circuit. P.D. is therefore also measured in volts.
Potential difference is also the work done in moving charge between the two points with work done being measured in joules. Therefore:
1 volt is hence equal to 1 joule per coulomb of charge.
Measuring potential difference
A voltmeter is used to measure the potential difference in a circuit. They are connected in parallel with the two points between which the p.d. is to be measured, such as before and after a bulb. In order to get an accurate reading the voltmeter must have a high resistance in order to keep the electrons from diverting around the bulb. An ideal or perfect voltmeter has infinite resistance.
Series and parallel circuits
In a series circuit there is only one route for the electrons to go and so the energy they deliver is split across the components of the circuit. The total potential difference of a series circuit is equal to the sum of the p.d.s across all the components of the circuit.
In a parallel circuit the electrons have multiple paths to choose from and so can give all their energy to a single component of the circuit. Therefore the total voltage of the circuit is equal throughout all branches of the circuit.