The idea
Electrons can be moved from one object to another. An object with extra electrons is negatively charged; one short of electrons is positively charged.
Protons never move. Only electrons do. Say “this object lost electrons” rather than “it gained protons” — the second is wrong.
Three ways to charge something
| Method | What happens | Contact? |
|---|---|---|
| Friction | Rubbing transfers electrons between materials | Yes |
| Conduction | Charge flows between touching conductors | Yes |
| Induction | A nearby charge pushes electrons within an object | No |
graph LR A["Neutral object"] -->|"rub with cloth"| B["Electrons transferred"] B --> C["One object negative, the other positive"] C -->|"like charges"| D["Repel"] C -->|"opposite charges"| E["Attract"]
The law of electric charges
- Like charges repel
- Opposite charges attract
- A charged object attracts a neutral one
The third one is the interesting one
Why does a charged balloon stick to a neutral wall? The balloon’s charge pushes the wall’s electrons slightly away, leaving the near surface slightly opposite in charge. Attraction to the closer side beats repulsion from the farther side. This is induced charge separation.
Why winter is sparky
Charge leaks away through moisture in the air. Cold air holds little water vapour, so charge accumulates instead of draining — which is why doorknobs start biting in January and not in September.
Curriculum connection
D2.1
conduct investigations to explain the behaviour of electric charges in static and current electricity, and to relate the observed behaviour to the properties of subatomic particles and atomic structure
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D2.2
determine the conductivity of various materials by investigating their ability to hold or transfer electric charges
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