Introduction to electricity - Higher physics. Measuring current, voltage, series and parallel circuits

1. Electricity
6D: Monday 22nd
November

2. 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:

3. 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

4. Measuring voltage
• We use an Voltmeter to measure voltage
across a component:
Vsupply
Vlamp
Ilamp

5. 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

6. 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 + …

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. 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. 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. 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 = …