Where Electricity Comes From
FoundationAtoms have a positive nucleus and negative electrons; charge sitting still is static electricity, charge flowing is current. Batteries and power stations both drive charge to flow.
- Static electricity is charge sitting still; current is charge flowing.
- An atom has a positive nucleus and negative electrons.
- Friction transfers charge; like charges repel and unlike charges attract.
文體小知識：科普知識文章用生活實例解釋科學概念，先看現象再講原理，讀完就能解釋日常見到的東西。
§Text Passage
1On a dry winter day a door handle gives you a sudden snap, and a balloon rubbed on your hair sticks to the wall — both are static electricity. To understand electricity we must enter the invisible microscopic world: all matter is made of atoms, each with a positive nucleus at the centre and negative electrons around it.
2Friction can transfer electrons from one object to another: brushing your hair leaves electrons on the comb, charging it so it attracts tiny paper bits. When accumulated charge is released all at once, that is a discharge — lightning is one giant discharge between clouds and the ground.
3When charge does not discharge in one go but flows steadily in one direction along a wire, we get electric current. Driving the flow needs a source: a battery converts stored chemical energy into electrical energy, while the electricity at home is generated in power stations and delivered through cables to every household.
4In the next lesson we connect a battery, wires and a bulb into a complete circuit and watch current travel all the way round the loop.
1Summary 重點摘要
Atoms have a positive nucleus and negative electrons; charge sitting still is static electricity, charge flowing is current. Batteries and power stations both drive charge to flow.
2Vocabulary cards Vocabulary
The build-up of electric charge on a surface where it does not flow, e.g. a comb after brushing hair picking up paper bits.
A basic property of matter, either positive or negative; like charges repel and unlike charges attract.
The basic unit of matter, made of a central nucleus with electrons moving around it.
Tiny negatively charged particles moving round the nucleus; some electrons in metals are free to move.
The positively charged centre of an atom, made of protons and neutrons.
The flow of electric charge in one direction; in metal conductors it is the flow of free electrons.
A source that converts chemical energy into electrical energy, driving electrons round a circuit.
The sudden release of accumulated charge, e.g. lightning.
A facility that generates electricity on a large scale and sends it to homes and factories through cables.
3Step by step Steps
- Meeting static electricityStatic electricity is the earliest electrical phenomenon we meet: brush dry hair several times with a plastic comb and it lifts tiny paper bits, because brushing transfers charge from hair to comb; the charged comb then attracts light objects. The drier the hair, the more easily charge builds up, so the effect is strongest in dry winter weather, while humidity lets water vapour carry charge away and weaken it. The crackle when taking off a sweater is also static discharging.
- Atoms and chargeAll matter is built from atoms, each with a positive nucleus at the centre and negative electrons moving around it. Normally the positive and negative charges are equal and cancel, so the atom is neutral overall. When electrons leave an atom, it becomes positive because its positive charge now exceeds its negative; an atom that gains extra electrons becomes negative. Charged atoms or molecules are collectively called ions.
- Charging by frictionWhen two different materials are rubbed together, electrons transfer from one to the other: a balloon rubbed on a jumper carries extra negative charge and clings to the wall until the charge slowly leaks away. Note that friction only transfers charge and never creates it — the total charge stays the same, in line with conservation of charge. Different materials attract electrons with different strengths, which is why one gains electrons while the other loses them.
- Like repels, unlike attractsCharges interact by a clear rule: like charges repel and unlike charges attract. Two rods rubbed with the same cloth carry like charge and push each other apart when brought close, while a rubbed rod and the cloth carry unlike charge and attract. To predict attraction or repulsion, first work out what charge each object carries. The stronger the static charge, the clearer the force, sometimes even producing sparks.
- From static to currentStatic and current electricity are the same in nature and differ only in how charge moves: lightning is a huge one-off discharge between clouds, or between cloud and ground, lasting only an instant. When charge flows steadily in one direction along a wire, it forms an electric current that can power appliances continuously. Batteries and power stations exist precisely to turn one-off discharges into steady current for long use.
- The role of a sourceA source is the heart of a circuit: a battery converts chemical energy into electrical energy and keeps pushing electrons round the circuit, while mains electricity is generated in power stations and delivered through cables to every socket. Without a source to drive them, charges will not keep flowing and the bulb stays dark. Batteries suit portable devices, while the mains supplies high power — the two complement each other for different needs.
4Diagrams Diagrams
5Worked example Example
Example: in dry winter weather, taking off a sweater often brings crackles and even tiny sparks in the dark. Explain with static electricity.
- Pulling the sweater over your head rubs it against your clothes, transferring charge that builds up on the surfaces.
- The accumulated charge grows until the potential difference against your skin is large.
- Charge suddenly jumps across the air gap, discharging and neutralising itself.
- The discharge heats the air quickly so it glows — hence the spark and the crackle.
- Answer: Pulling off the sweater rubs it against other clothes, transferring charge that builds up on the surfaces; the more it builds up, the larger the potential difference against your skin, until charge suddenly jumps across the air and neutralises. The discharge heats the air so quickly that it glows, which is why sparks are seen in the dark and crackles are heard. This is the complete process of friction charging, build-up and discharge.
6Common mistakes Mistakes
7Quick check Quick check
Q1A plastic comb after brushing dry hair lifts paper bits. What phenomenon is this?
Q2What charge does an electron carry?
Q3How do like and unlike charges interact?
Q4What energy does a battery convert into electrical energy?
Q5Is lightning static electricity or current? Why?
8Recap Recap
- Static electricity is charge sitting still; current is charge flowing.
- An atom has a positive nucleus and negative electrons.
- Friction transfers charge; like charges repel and unlike charges attract.
- Lightning is a huge natural discharge of accumulated charge.
- Batteries convert chemical energy to electrical energy to drive electrons round a circuit.