PHYSICS · Stage 7 · Chapter 4: Electricity
Physics 4.6 Chapter 4 Review: Electricity
5 min read 5 parts Lesson 6 of 6
Lesson summary
4.6 Chapter 4 Review: Electricity — Alhussan International Academy — Physics (Stages 7–9) notes: Revise static charge, current, series circuits, circuit models, two-way switches and electrical safety.Charging — rubbing a balloon on a jumper transfers electrons from the jumper to …
- Sticking to a wall
- Conservation
- Insulators and conductors
- Chain of changes
- Net charge
- Resistance
Section 1 of 5Static charge and the sticking balloon
- Charging
- rubbing a balloon on a jumper transfers electrons from the jumper to the balloon, so the balloon has a net negative charge.
- Sticking to a wall
- the wall is an insulator and neutral overall.
- The negative charge on the balloon repels the electrons in the wall's surface away, leaving the surface slightly positive.
- The balloon is attracted to this positive surface, and the attraction is enough to hold it up.
- Conservation
- charge is conserved, so when the balloon gains electrons the jumper loses the same amount.
- Insulators and conductors
- insulated objects keep a charge, but conductors let it flow away.
Section 2 of 5Current, resistance and measuring
- Current
- the flow of charge, measured in amperes with an ammeter connected in series.
- Series circuit
- adding lamps increases the resistance and reduces the current, while adding cells increases the current.
- The same current passes through every component, and a switch must be closed for any current to flow.
- Conductors
- metals and graphite let charge flow.
- Insulators
- plastic, wood and glass do not.
Section 3 of 5Models of circuits
1Models2 points
- a circuit can be modelled with a loop of rope or as trucks delivering food to a supermarket.
- The battery or pusher drives the flow, the loop carries it round, and energy is delivered where it is needed.
2Limits2 points
- all models have limits and should be tested against evidence.
- A model with limits is not wrong, and it should be judged by one strength and one limit.
Section 4 of 5Two-way switches
- Use
- some circuits use two switches to control one lamp, such as a staircase light.
- Operation
- one switch can be flipped between connections 1 and 3, and the other between connections 2 and 4.
- The lamp is on only when the two switches connect to form a complete loop through the cell.
- Flipping either switch changes this, so the light can be switched on or off from either place.
Section 5 of 5Cause and effect in circuits
- Chain of changes
- a change in one factor starts a chain of responses.
- Adding a lamp raises the resistance, which lowers the current, which makes each lamp dimmer.
| Idea | Key fact |
|---|---|
| Static charge | Rubbing transfers electrons; like charges repel, unlike attract |
| Current | Flow of charge, measured in A with an ammeter in series |
| Conductors | Metals and graphite let charge flow |
| Insulators | Plastic, wood and glass keep charge in place |
| Series circuit | More lamps means more resistance and less current |
| Safety | Earthing lets charge flow safely to the ground |
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