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# 3 e electronics 231110

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Measuring voltage in series and parallel circuits, uses of parallel and series circuits: S3

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### 3 e electronics 231110

1. 1. Electricity 3E: Tuesday 23rd November
2. 2. Measuring current • Current (flow of charge) has symbol I, and is measured in Amperes (A) • We use an Ammeter to measure current through a circuit • Ammeter is connected in line with the other components – in series – We ‘break into’ the circuit:
3. 3. Voltage • Voltage (or potential difference) has symbol V, and is measured in Volts (V) • Voltage of a supply is a measure of the energy given to charges in a circuit: A voltage of 1V means 1 Joule (J) of electrical energy is being transferred into other forms every time 1 Coulomb (C) of charge passes through a component •1 Volt = 1 Joule per Coulomb OR 1V = 1JC-1
4. 4. Measuring voltage • We use an Voltmeter to measure voltage across a component: Vsupply Vlamp Ilamp
5. 5. Experiment: • Aim: Measuring voltage in a series circuit • Working in pairs: – Collect 3 cells, 4 lamps, 10 wires, 1 Ammeter and 1 Voltmeter • A) Measure the Voltage of the supply and the voltage across each of the lamps in the series circuit (Experiment A) as per last class • Write down your results in a table
6. 6. Series circuits: Conclusions • The voltage of the supply is equal to the sum of the voltages across all the components in the circuit: • Vsupply = V1 + V2 + V3 + … • When more bulbs are added to the series circuit the current is reduced • The current is the same at ALL points within the series circuit: • Isupply = I1 = I2 = I3 = …
7. 7. Parallel circuits • In a parallel circuit, current has more than one path in which to flow around the circuit: Vsupply I1 I2 I3 V1 V2 V3 Isupply
8. 8. Experiment • Aim: Measuring current and voltage in a parallel circuit • Set up parallel circuit as shown • Measure the voltage across the cells (Vsupply) and the voltage across each lamp (V1, V2, V3, V4) • Measure the current through each lamp (I1, I2, I3, I4) and the current drawn from the supply, Isupply
9. 9. Parallel circuits: Conclusions • The sum of all currents in the parallel branches in the circuit is equal to the current drawn from the supply: • Isupply = I1 + I2 + I3 + … • The voltage across components in parallel are the same and equal to the supply voltage • Vsupply = V1 = V2 = V3 = …
10. 10. Uses of series circuits • Torches, old-style Christmas lights… • Stair lighting uses two or more 2-way switches in series: Power Supply Downstairs switch Upstairs switch Lamp This circuit is in the OFF position Either switch will turn the light ON
11. 11. Uses of parallel circuits • New style Christmas lights • Car lighting circuits: MM Ignition switch Side & rear lamps Headlights Starter motor Wiper motor