Electricity

6D: Monday 22nd November

Measuring current

• Current (flow of charge) has symbol I, and is measured in Amperes or Amps (A) for short

• 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:

Voltage

• Voltage (or potential difference) has symbol V, and is measured in Volts (V)

• Voltage tells us how much energy is transferred by a component 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

Measuring voltage

• We use an Voltmeter to measure voltage across a component:

Vsupply

Vlamp

Ilamp

Experiments:• Aim: Measuring current and voltage in a series circuit• Working in pairs:– Collect 3 cells, 4 lamps, 10 wires, 1 Ammeter and 1

Voltmeter

• A) Measure the current in the circuit for 1, 2, 3 and 4 bulbs

• B) Measure the current at different points within our circuit containing 4 bulbs, and the voltage across all 4 bulbs

• Write down your results in a table

Series circuits: Conclusions

• 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 = …

• The voltage of the supply is equal to the sum of the voltages across all the components in the circuit: • Vsupply = V1 + V2 + V3 + …

Parallel circuits• In a parallel circuit, current has more than one

path in which to flow around the circuit:

Vsupply

I1I2 I3

V1V2 V3

Isupply

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

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 = …