Electric Charge and the Process of Charging
Introduced| English |
|---|
| electrons/ɪˈlektrɒnz/ |
| insulators/ˈɪnsjuːleɪtəz/ |
| conductor/kənˈdʌktə/ |
| polarises/ˈpəʊləraɪzɪz/ |
| ground/ɡraʊnd/ |
| conservation of charge/ˌkɒnsəˈveɪʃn ɒv tʃɑːdʒ/ |
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?
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 ____.
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 same sign as the source.
Contact shares charge, so both end with the same sign.
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:
Induction leaves the opposite sign — a positive rod leaves a negative sphere.
Select all correct statements about charging.
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 ____.
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.