Circuit Symbols – you met these circuit symbols in GCSE Physics.
Conventional current flows around a circuit from the positive (+) side of the cell to the negative (). However the electrons are flowing around the circuit in the opposite direction from the negative () side of the cell to the positive (+).
Charge, Current & Potential Difference
Charge (Q) – charge is measured in coulombs (C).
 A single electron carries a charge of 1.6 x 10^{19} C.
Current (I) – is measured in amperes (A).
 Current is the rate of flow of charge. A current of 1 A means that 1 coulomb of charge flows past a point in a circuit every second. ( 1 A = 1 C s^{1} ) Current is measured in a circuit using an ammeter which is placed in series with the component of interest in the circuit.
 I = current in amperes, A
 DQ = charge in coulombs, C
 Dt = time in seconds, s
Potential difference (V) – is measured in volts (V).
 Potential difference is the work done per unit charge. A potential difference of 1 V means that 1 joule of work is done per coulomb of charge. ( 1 V = 1 J C^{1}) Potential difference in a circuit is measured using a voltmeter which is placed in parallel with the component of interest in the circuit.
 V = potential difference in volts, V
 W = work done or energy transferred in joules, J
 Q = charge in coulombs, C
Resistance (W) – is the ratio of potential difference across a component to the current flowing through it, it is measure in ohms (W).

R = resistance in ohm’s, W

V = potential difference in volts, V

I = current in amperes, A
Examples;
Q1) If all electrons carry a charge of 1.6 x 10^{19} C, how many electrons would be needed to give a total charge of one coulomb?
Q2) If a current of 0.50 amps flows through a circuit for 120 seconds. How much charge will have passed into a component in the circuit?
Q3) A charge of 4.0 coulombs was moved through a potential difference of 24 volts, how much energy was transferred?
Q4) The potential difference across a component is 12 volts and the current through it is 0.37 amps, what is the resistance of the component?