Unit 9: Electricity
Current And Voltage In Parallel Circuits — HIA International - Grade 8 Revision Notes & Topical Questions
5 min read 10 parts Lesson 8 of 12 1 quiz
Lesson summary
Current and voltage in parallel circuits — HIA INTERNATIONAL notes: Compare current and voltage in series and parallel circuits and state the effect of adding cells and lamps.Voltage = a measure of the electrical energy in a circuit, measured in volts (V).It measures the energy s…
- It measures the energy supplied by a cell, battery or power supply
- Most cells supply 1.5 V
- Mains voltage
- Voltage rating
- In a circuit diagram
- Energy is conserved
Section 1 of 10Voltage
Voltage
Voltage
Voltage a measure of the electrical energy in a circuit, measured in volts (V).
It measures the energy supplied by a cell, battery or power supply
- It measures the energy supplied by a cell, battery or power supply and the energy changed by components such as lamps.
Most cells supply 1.5 V
- Most cells supply 1.5 V batteries commonly supply 6 V, 9 V or 12 V.
Mains voltage
- Mains voltage between 220 V and 240 V in most countries, and 110 V in some.
Voltage rating
- Voltage rating the maximum voltage a component can use; school lamps are often rated 3 V or 6 V.
Section 2 of 10Measuring current and voltage
Ammeter
- Ammeter measures the current through a component, so it is connected in series with it.
Voltmeter
- Voltmeter measures the energy difference across a component, so it is connected in parallel with it.
In a circuit diagram
- In a circuit diagram the ammeter is in the loop with the lamp and the voltmeter is across the lamp.
Section 3 of 10Voltage in a series circuit
Voltage in a series circuit
Energy is conserved
- Energy is conserved the energy changed by the components equals the energy supplied by the supply.
The voltages across the components add up to the supply voltage.
Identical components
- Identical components have the same voltage across each.
Different components
- Different components the one that changes more energy has the larger voltage, for example a lamp compared with a buzzer.
The current is the same all the way round
- The current is the same all the way round because there are no branches.
Section 4 of 10Adding components in series
Adding components in series
Adding components
- Adding components gives each component a smaller share of the voltage.
Adding components decreases the current
- Adding components decreases the current it is harder for the supply to push electrons round.
Adding cells increases the supply voltage
- Adding cells increases the supply voltage two 1.5 V cells give 3 V, and a 12 V battery contains eight 1.5 V cells.
More cells in series increase the current
- More cells in series increase the current and the voltage across each component.
Section 5 of 10Current and voltage in a parallel circuit
1The voltage across every branch equals the supply voltage
- The voltage across every branch equals the supply voltage even when the components in the branches are different.
2The current can be different in each branch
- The current can be different in each branch because the current has different paths to flow along.
3
The current through the cell equals the sum of the branch currents.
4
A branch with lower resistance takes a larger share of the current.
Section 6 of 10Adding components in parallel
Adding components in parallel
Adding another branch
- Adding another branch gives more paths for the current, so the current through the cell increases.
Other branches are not affected
- Other branches are not affected and lamps stay at the same brightness.
Adding components to one branch
- Adding components to one branch decreases the current in that branch, because the branch voltage stays the same.
Adding cells to a parallel circuit
- Adding cells to a parallel circuit increases the supply voltage, the voltage across each branch, the current through the cell and the current through each branch.
Section 7 of 10Series and parallel circuits compared
| Feature | Series | Parallel |
|---|---|---|
| Current | Same everywhere | Splits between branches and adds up to the total |
| Voltage | Shares the supply voltage between components | Same across every branch |
| Adding a lamp | Current falls; lamps dimmer | Total current rises; other lamps unchanged |
| If one component breaks | All stop | Others keep working |
Section 8 of 10Measuring voltage in a series circuit
1
Set up a series circuit with a battery, two lamps and a buzzer, without exceeding any voltage rating.
2
Connect the voltmeter across the battery and record its voltage.
3
Connect the voltmeter separately across each component and record each voltage.
4
Record the results in a table.
5
Add the voltages across the components and compare the total with the battery voltage.
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Voltage | A measure of the electrical energy supplied or changed in a circuit, in volts. |
| Voltmeter | A meter connected in parallel to measure voltage. |
| Voltage rating | The maximum voltage a component can safely use. |
| Mains | The electrical supply from a power station or generator. |
| Supply | The cell, battery, power supply or mains that provides energy. |
| Branch | One path of a parallel circuit. |
| Series circuit | A circuit with one path for the current. |
| Parallel circuit | A circuit with more than one path for the current. |
Section 10 of 10Exam technique
1
Connecting a voltmeter in series — it must be connected in parallel across the component.
2
Saying the voltage is shared between parallel branches — each branch has the full supply voltage.
3
Saying adding lamps in parallel dims the others — their brightness stays the same.
4
Saying the current is the same in all parallel branches — it differs unless the branches are identical.
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