PHYSICS · Stage 7 · Chapter 4: Electricity
Physics 4.4 Modelling electric circuits — Conductors, Insulators and Scientific Models
5 min read 5 parts Lesson 4 of 6
Lesson summary
4.4 Modelling electric circuits — Conductors, Insulators and Scientific Models — Alhussan International Academy — Physics (Stages 7–9) notes: Describe models of an electric circuit and evaluate the strengths and limitations of each.Problem — you cannot see a current flowing in a …
- What it shows
- Predictions
- Factory model
- Sweets model
- Water model
- Faulty battery
Part 1 of 5Why we use models
1Problem
— you cannot see a current flowing in a wire, which makes it hard to understand what is happening in a circuit.
2Model1 point
= a helpful way of thinking about something that you cannot see, or that is very big or very small.
- Scientists use models to work out what is happening and to predict what might happen in different circuits.
3Limits1 point
— all models have limits, meaning there may be things they do not explain clearly, or at all.
- A good scientist asks where each model works and where it fails.
Part 2 of 5The rope model
- Set-up — a rope is tied in a continuous loop, with one person as the "battery" and another as the "lamp".
| The rope is like... | In an electric circuit... |
|---|---|
| The rope | The charges (electrons) in the wire |
| Person X pulling the rope | The cell or battery pushing the charge |
| Rope passing through his hand each second | The current (charge flowing per second) |
| Person Y gripping the rope gently | A component, like a bulb |
- Energy — Person Y's hands get warm, like the filament of a lamp, which gets so hot that it gives out light.
- The rope transfers energy from person X to person Y, as the current transfers energy from the battery to the components.
- What it shows — the battery does not produce the charges, which are already in the wires and components.
- The same amount of rope passes any point every second, so the current is the same everywhere in a series circuit.
- All parts of the rope start to move as soon as person X starts, so current starts to flow as soon as the battery is connected.
- Predictions — a second lamp is like a second person holding the rope, so there is more resistance to its movement.
- Strengths — it helps us to visualise what is happening and make predictions.
- Limits — lamps in a circuit light up immediately, which this model does not explain well, and it does not help predict what happens with more than one lamp.
Part 3 of 5The factory and people model
- Factory model — the factory that makes things such as loaves of bread represents the battery, the trucks are like the charges, and the shop is like the lamp.
- The bread represents the energy.
- Sweets model — a pot of sweets is like the battery, the people carrying the sweets are like the charges, another person eating the sweets is like the lamp, and the sweets represent the energy transferred from the battery to the lamp.
- Limit — lamps light up immediately and the models do not explain that very well.
Part 4 of 5The water circuit model
1Water model1 point
— the pipes are like the wires, the water is like the charges, the pump pushes the water around the pipe like a battery, the tap can stop the flow like a switch and a flow meter measures the flow like an ammeter.
- Making the water move faster represents a bigger current.
2Limit2 points
— some people think the insulation around a copper wire holds the electrons in, like a pipe holding the water in.
- This is not correct, because water can leak out of pipes but electrons cannot leak out of wires.
- Insulation stops current flowing to other places or people.
3Faulty battery
— in each model it is represented by a pump, person or factory that does not work.
4Switch
— in the rope or truck model it could be represented by a person who stops the rope or a road block that stops the trucks.
| Model | Battery is like | Current is like | Main limit |
|---|---|---|---|
| Rope | Person pulling the rope | Rope passing a point each second | Does not explain instant lighting or several lamps |
| Factory or trucks | Factory | Goods delivered | Does not explain instant lamp lighting |
| Water pipe | Pump | Water flow | Wires are not hollow pipes and electrons do not leak |
Part 5 of 5Using models
- Helpingmodels help us work out what is happening in a circuit.
- Predictingmodels can be used to predict what might happen if you change something in a circuit.
- Limitationsall models have limitations.
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