1. Circuits – Current and Voltage

2. Quick Starter Complete the Handout called ‘Voltage’ –Definitions of terms that you should be familiar with When finished, draw in your exercise books a circuit that shows: a)2 bulbs in series b)2 bulbs in parallel

3. In an electric c____, current is the flow of e_______. The bigger the current, the m___ electrons are flowing around the circuit. The w___ carry the electrons from one terminal around the circuit to the other t______. Current lamps ircuit lectrons ore ires erminal

4. Set up the two circuits shown: In which circuit are the bulbs the brightest? In circuit A the bulbs are the brightest. What happens if you unscrew one bulb in Circuit A? The other bulb stays lit. What happens if you unscrew a bulb in circuit B? The other bulb goes out. What do we call circuit A? Parallel Circuit What do we call circuit B? Series Circuit BRIGHTER DIMMER A. B.

5. Measuring current I Set up the circuit shown below…… …and then record the current using an ammeter in the places shown below. What do you notice about the readings? The current is the same for each ammeter. In a series circuit the current is the same wherever you measure it. When measuring current ammeters are always placed in series. A A A

6. Measuring current II Set up the circuit shown below…… …then record the current at the locations shown.What do you notice about the readings? For a parallel circuit, the current that leaves the cell or battery is the same as the current that returns to the cell or battery. The current does not get used up by a circuit, just the energy the electrons are carrying. A 1 = A 4 The sum of the currents in the branches of a parallel circuit is the equal to the current that leaves the cell or battery. A 1 = A 2 + A 3 =A 4 AmmeterCurrent (A) A1A1 A2A2 A3A3 A4A4 0.8 0.4 A1A1 A2A2 A3A3 A4A4

7. The v_____ is a measure of how big a push the e_______ are given as they leave the cell or b_____. The bigger the voltage, the bigger the p___. The cell, battery or p____ s_____ produces the voltage. Voltage lamps oltage lectrons attery ush ower upply

8. Measuring voltage I V2V2 V3V3 V1V1 Set up the apparatus as shown…… …then record the voltages at the locations shown. What do you notice about the readings? For a series circuit, the sum of the voltages for each component is equal to the voltage across the cell or battery. V 1 = V 2 + V 3 Voltmeters are connected in parallel VoltmeterVoltage (V) V1V1 V2V2 V3V3 1.5 0.75

9. Measuring voltage II V1V1 V2V2 V3V3 VoltmeterVoltage (V) V1V1 V2V2 V3V3 1.5 Set up the apparatus as shown…...measure the voltage at the locations shown. What do you notice about your readings? For a parallel circuit, the voltage across the cell/battery is the same as the voltage across each branch. V 1 = V 2 = V 3

10. Testing Your Knowledge Complete the handout Make sure that you read the instructions carefully

11. High Demand – Calculation Fun It is possible to work out the charge flowing through a circuit at any given time using the following equation: Q = I x t where: –Q = charge (measured in Coulombs (C)) –I = current (measured in Amperes (A)) –t = time (measured in seconds (s))

12. Knowing the charge, it is also possible to calculate the amount of energy supplied to a bulb using the following formula: E = V x Q where: –E = energy (measured in Joules (J)) –V = voltage (measured in Volts (V)) –Q = charge (measured in Coulombs (C)) Can you see how it is possible to work out the energy if you were not given the charge but were given current and time instead?

13. Example A portable emergency light can run from a 12V car battery and draws a current of 5A. a)How much charge passes through the bulb in 90 seconds? b)Calculate how much energy it takes to run the bulb for 90 seconds. c)Re-calculate your answer for b) using a different method/formula