Electric Charge LO: To explain voltage in terms of work done by the moving charges Complete the missing words: 1.Electricity is the flow of _____________ around a circuit. 2.A proton is a ____________ charge (positive / negative). 3.An electron carries a ________________ charge. 4.The current can be calculated from charge flowing divided by the _____ taken. 5.Charge is measured in _____________.

Recap: Electric current is the flow of charge. Electrons are charged (negatively) The more charges go past a point in a given time; the higher the current I = Q / T Current (A) = Charge (C) / Time (s)

Theory bit: Copy this simple circuit The ammeter is in series, it is measuring the ‘rate of flow’ of charges (i.e. total charge / time taken) The voltmeter is in parallel. It is measuring the energy provided to the bulb by each charge. (another way of saying this is it measures the difference in the energy per charge going in and leaving the bulb)

Pupil demo Tokens = energy (work done) Pupils = electrons. Room = circuit Pupil hands out tokens = cell 1 Pupil collects token = bulb 1 Pupil counts number of electrons that go past in a given time = ammeter 1 Pupil counts the difference between the number of tokens going into and leaving the bulb = voltmeter 1 pupil needs to add up the total amount of energy given to the bulb in the time limit. (work done)

Proving the equation: We will run the circuit a few times, using different Voltages to see if the rule works. Try the circuit for voltages of 1, 2 and 3 V (this means handing out 1, 2 or 3 tokens at a time)

Does our model actually work? Voltage (potential difference) Work done (total number of tokens collected at bulb) Total charges ( number of pupils past the ammeter) Work done divided by charge Copy this table out, for the last column use the equation of Potential Difference = Work done ÷ Charge If our model has worked the last column should be the same as the first.

Theory bit: 1 Volt is the potential difference when 1 Joule of work is done by 1 Coulomb of charge. Potential Difference = Work done ÷ Charge (V) (J) ÷ (C)

Practice makes _______. For these questions find the Voltage (potential difference) if: 1) 1200J of work is done by 300 C of charge 2) 160 J of work is done by 40 C of charge 3) 21 J of work is done by 7 C of charge Find the Work done if: 4) Voltage = 3V and the charge is 10 Coulombs 5) Voltage = 5 V and the charge is 5 C 6) Voltage = 10 V and the charge is 0.4 C

A harder question: Find the potential difference across a bulb if a Current of 2 Amps flows in a time of 3 seconds doing a Work of 12 Joules.