PHYSICS · Stage 9 · Chapter 14: Electrical Circuits, Resistance and Power
Physics 14.6 Chapter 14 Review: Electrical Circuits, Resistance and Power
5 min read 6 parts Lesson 6 of 6
Lesson summary
Physics 14.6 Chapter 14 Review: Electrical Circuits, Resistance and Power — Alhussan International Academy — Physics (Stages 7–9) notes: Summarise Chapter 14 on series and parallel circuits, current, voltage, resistance, power and electrical energy.FeatureSeriesParallelLoopsOne l…
- Independent control
- Unscrew each bulb in turn
- All others go out
- Only the removed bulb goes out
- Some go out
- Energy in kWh
Section 1 of 6Series and parallel circuits
| Feature | Series | Parallel |
|---|---|---|
| Loops | One loop | More than one loop (branches) |
| Current | Same everywhere | Branch currents add up to the battery current |
| Voltage | Shared; adds up to the battery voltage | Same across every branch |
| Switch | One switch controls all components | A switch in a branch controls only that branch |
| If one lamp breaks | All go out | The others stay on |
Section 2 of 6Switches
- Series
- One switch controls all components because it breaks the only loop.
- Parallel
- A switch in a branch controls only that branch, whereas a switch in the main wire controls everything.
- Independent control
- If every component must switch on and off independently, each needs its own switch in its own branch.
Section 3 of 6Finding how bulbs are connected
- Unscrew each bulb in turn
- Watch the effect on the other bulbs.
- All others go out
- The bulbs are in series.
- Only the removed bulb goes out
- The bulbs are in parallel.
- Some go out
- The circuit is a mixture of series and parallel.
Section 4 of 6Meters
- Ammeter
- A circle with A, connected in series to measure current.
- Voltmeter
- A circle with V, connected in parallel across a component to measure voltage.
| Quantity | Unit | Meter |
|---|---|---|
| Current | ampere (A) | Ammeter in series |
| Voltage | volt (V) | Voltmeter in parallel |
| Resistance | ohm (Ω) | Calculated from V ÷ I |
Section 5 of 6Key equations
- Resistance
- R = V ÷ I.
- Power
- P = E ÷ t, in watts, joules and seconds.What the symbols mean: P = power (W = J s−1) · W or E = work done / energy transferred (J) · t = time (s) · F = force (N) · v = velocity (m s−1)
- P = E ÷ t, in watts, joules and seconds.
- Energy in kWh
- Energy = power in kW × time in h.
- Sense checks
- A branch current can never exceed the current from the battery, and a voltage across one component in series can never exceed the battery voltage.
Section 6 of 6Resistance in circuits
- Resistors
- A resistor in series with a lamp reduces the current.
- Series
- Resistances add and the current is the same.
- Parallel
- The voltage is the same and adding a branch reduces the overall resistance.
Last updated: