The Process of Charging
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| electron/ɪˈlektrɒn/ | Electron |
That doorknob spark — where did the charge come from?
- Walk across a carpet and touch a doorknob: snap — a tiny shock.
- You picked up extra electrons 电子 from the carpet, then dumped them into the metal.
- Charging is really just electrons moving from one object to another.
- There are a few tidy ways to make an object charged.
Charging by friction
- Rub two different materials together and electrons transfer from one to the other.
- One object ends up with extra electrons (negative), the other short of them (positive).
- The balloon-and-hair and carpet-and-shoe effects both work this way.
- No charge is created — it is only moved.
Rub up a charge
Rub the balloon and watch electrons transfer, then see it attract a wall or hair.
Charging by friction transfers ____ from one material to the other.
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Rubbing moves electrons; one object gains them, the other loses them.
Conduction and induction
- Charging by conduction — touch a charged object to a neutral one; charge flows across by contact.
- Charging by induction — bring a charge near (without touching), and it rearranges charge in the other object.
- Induction can leave a conductor charged even though nothing touched it.
- Both, like friction, only shuffle electrons around.
Charging by induction differs from conduction because it:
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Induction rearranges charge by proximity — no contact is needed.
Select all genuine methods of charging an object.
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Friction, conduction and induction all charge objects. Heating alone does not.
Charge is conserved
- Conservation of charge: charge is never created or destroyed, only transferred.
- If one object gains $-5\ \text{units}$, another gains $+5$ — the total is unchanged.
- In everyday charging it is always electrons that move (protons stay locked in nuclei).
- So a "positive" object is really one that has lost some electrons.
In ordinary charging, which particles actually move between objects?
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Electrons transfer; protons stay locked in the nuclei.
A positively charged object has:
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A positive object has lost electrons, leaving more protons than electrons.
When one object gains negative charge, another object must lose the same amount.
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Charge is conserved: it is transferred, never created or destroyed.
In ordinary charging, it is electrons that move — never protons. A positively charged object has lost electrons, not gained protons. And no charge is ever created: what one object gains, another loses (conservation of charge).
A glass rod is rubbed with silk and becomes positive with charge $+3\ \text{units}$.
- The rod lost $3\ \text{units}$ of electrons.
- The silk gained exactly $3\ \text{units}$ of electrons, becoming $-3$ — the total stays zero.
Charging moves electrons between objects — by friction (rubbing), conduction (contact) or induction (nearby, no contact). Charge is conserved: what one gains, another loses. A positive object has lost electrons, never gained protons.
Write from a cloth charge of -3 nC
- A neutral rod and a neutral cloth are rubbed together.
- The rod ends at positive 3 nC. Find the cloth's charge.
A neutral rod is rubbed on a neutral cloth. The rod ends with a charge of positive 3 nC. What is the cloth's charge, and what is the total charge of rod plus cloth?
The rod's positive 3 nC means the cloth lost that much negative charge.
What is the cloth's charge after rubbing?
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The cloth supplied the electrons, so it is left at -3 nC. Other options — Positive 3 nC (the same sign as the rod); 0 (as if both objects stayed neutral).