Electric Charge and the Process of Charging
Introduced| English | Meaning |
|---|---|
| electrons/ɪˈlektrɒnz/ | Negatively charged subatomic particles found outside atomic nuclei. |
| insulators/ˈɪnsjuːleɪtəz/ | A material in which electric charge does not move readily under ordinary conditions. |
| conductor/kənˈdʌktə/ | A material through which electric charge or thermal energy can pass readily. |
| polarises/ˈpəʊləraɪzɪz/ | polarises |
| ground/ɡraʊnd/ | Connect a conductor to Earth so charge can enter or leave. |
| conservation of charge/ˌkɒnsəˈveɪʃn ɒv tʃɑːdʒ/ | The principle that total electric charge remains constant in an isolated system. |
Three ways to move charge — none of them make new charge
- You can charge an object, but you never create charge.
- Charging just moves electrons 电子 from one place to another.
- One object gains electrons (goes negative); the other loses them (goes positive).
- There are three ways to do it: friction, conduction, and induction.
When you charge an object, what actually moves?
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Charging moves electrons; protons stay locked in the nuclei.
Charging by friction
- Rub two different materials together and electrons rub off one onto the other.
- The material that grabs electrons becomes negative; the other becomes positive.
- This works best on insulators 绝缘体 like plastic or hair.
- The charge stays put where it was rubbed — insulators don't let it flow.
Rub and charge
Rub the materials and watch electrons transfer, leaving equal and opposite charges.
A material that does not let charge flow through it is called an ____.
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Insulators (plastic, hair, glass) hold charge where it is placed.
Charging by conduction
- Touch a charged object to a neutral conductor 导体 and charge flows across.
- They share the charge, so both end up with the same sign.
- Conductors let charge move freely, so it spreads over the surface.
- Break contact and the conductor keeps its share.
Charging by conduction (direct contact) leaves the object with the opposite sign to the source.
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False. Contact shares charge, so both objects end with the same sign. Opposite charge comes from charging by induction.
Charging by induction
- Bring a charged rod near (not touching) a conductor.
- The rod's field pushes like charges away and pulls opposite charges near — the conductor polarises 极化.
- Now ground 接地 the far side: unwanted charge escapes to the earth.
- Remove the ground, then the rod — the conductor keeps the opposite sign.
A positive rod charges a sphere by induction (with grounding). The sphere ends up:
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Induction leaves the opposite sign — a positive rod leaves a negative sphere.
Select all correct statements about charging.
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Friction suits insulators, induction is contactless, conduction shares sign. Charging never creates charge.
Charge is always conserved
- Add up the charge before and after: the total never changes.
- Electrons only move; they are not made or destroyed.
- This is the law of conservation of charge 电荷守恒.
- It holds for every charging method and every circuit.
The total charge before and after any charging process is the same — charge is ____.
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Charge is conserved; electrons only move.
You hold a negative rod near a metal sphere and ground the far side.
- The rod repels electrons to the far side, which then flow to ground.
- Remove the ground, then the rod: the sphere is left positive — opposite to the rod.
Conduction leaves the same sign as the source; induction leaves the opposite sign. Mixing these up is the classic charging mistake — check whether the source actually touched the object.
Charging moves electrons, never creates them. Friction and conduction leave the same sign as the source; induction (polarise, then ground) leaves the opposite sign. In every case, charge is conserved.
Write from a shared charge of -4 microcoulomb
- A rod carrying -8 microcoulomb touches a neutral metal sphere and they share the charge equally.
- Find the charge on each object. Say what induction plus grounding would have done instead.
A rod carrying -8 microcoulomb touches a neutral metal sphere and they share the excess equally. What charge does each end with, and how is induction different?
Equal sharing of -8 microcoulomb gives -4 microcoulomb each. Charging moves electrons. It does not create charge.
What charge does each object have after equal sharing?
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Half of -8 microcoulomb is -4 microcoulomb, and the two halves still add to -8 microcoulomb.