4.1Chapter 4: Electricity

Charging up — Alhussan Physics - Stage 7 Revision Notes & Topical Questions

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📚 Alhussan Physics - Stage 7 Hub / Topical Revision

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4.1 Charging up — Static Electricity, Electrons and Electrostatic Forces — Alhussan International Academy — Physics (Stages 7–9) notes: Name the two types of charge, explain why objects become charged, and explain the difference between conductors and insulators.Phenomenon = some…

Forces between charges
Charged balloon
Origin of the word
Atom model
Neutral atom
Which particles move

Part 1 of 7Electrostatic phenomena

Phenomenon

Phenomenon something that you can observe.

Examples

Examples a balloon rubbed on clothes sticks to a wall, deflects a stream of water from a tap and picks up small pieces of paper.
A comb rubbed through dry hair can attract a thin stream of water or small pieces of paper.
Clothes crackle when pulled apart because charge builds up by friction and then discharges.

Cause

Cause these things happen because rubbing charges the balloon.

Static

Static it means stationary or standing still, so electrostatic phenomena are caused by charges that are not moving.

Part 2 of 7What charge is

What charge is

Charge

Charge it is a property of a particle or object, like mass.

Two types

Two types positive (+) charge and negative (-) charge.

Forces between charges

Forces between charges when charges are brought together, electrostatic attraction or repulsion occurs.
Like charges repel, so a positive charge repels another positive charge and a negative charge repels another negative charge.
Unlike charges attract, so a positive charge attracts a negative charge.

Charged balloon

Charged balloon it can repel the negative charge in scraps of paper, running water or a wall, leaving a positive charge that produces attraction.

Origin of the word

Origin of the word in 600 BCE a Greek scientist picked up leaves with rubbed amber, and the Greek word for amber is elektron.

Part 3 of 7Charges in atoms

Charges in atoms

Atom model

Atom model protons and neutrons make up the central nucleus, and electrons orbit the nucleus.

Neutral atom

Neutral atom the number of electrons (negative) always equals the number of protons (positive), so the atom has no net charge and is neutral.

Which particles move

Which particles move only electrons move from one object to another, and protons stay in the nuclei.

Gaining or losing

Gaining or losing gaining electrons makes an object negative and losing electrons makes it positive.

Part 4 of 7How rubbing charges an object

1Polythene rod

Polythene rod when it is rubbed with a cloth, electrons are transferred from the cloth to the rod.
The rod has a net negative charge, because there is not enough positive charge to neutralise the negative charge.
The cloth has a net positive charge, because there is not enough negative charge to neutralise the positive charge.

2Perspex rod

Perspex rod when it is rubbed, electrons are transferred from the rod to the cloth,
- so the rod has a net positive charge and the cloth a net negative charge.

3Only some electrons

Only some electrons not all electrons are transferred, just some.

4Conservation of charge

Conservation of charge the total amount of charge in the rod and the cloth is always the same,
- since charge cannot be created or destroyed, just like energy or mass.

Object	Electron change	Net charge
Polythene rod (rubbed with cloth)	Gains electrons	Negative
Cloth rubbed on polythene	Loses electrons	Positive
Perspex rod (rubbed)	Loses electrons	Positive

Part 5 of 7Testing with rods

1Two polythene rods

Kunala rubbed a polythene rod and hung it by a string, then brought a second rubbed rod close, and the first rod was repelled.
Both rods are negatively charged, so the net charge on both is the same.

2Perspex rod

Perspex rod when a rubbed Perspex rod is brought near the polythene rod, it is attracted.
The rods have unlike charges, and the net charge on the Perspex rod is positive.

Part 6 of 7Electric field

Electric field the region around any charge where another charge experiences a force.

Part 7 of 7Insulators and conductors

Insulator

Insulator electrons stay on the rod once you have rubbed it, so the charge stays in place, as with polythene and Perspex.

Conductor

Conductor electrons can move in it, as in metals.
A metal rod rubbed with a cloth also becomes charged,
- but extra electrons move through the metal to your hand and through you to earth,
- so the rod seems uncharged.

Insulated person

Insulated person if charge is transferred to a person insulated from the ground, the charge stays on them.
Their hairs all gain the same charge, so they repel each other and the hair stands away from the body.

Key terms

Term	Meaning
Electrostatic	relating to electric charges that are stationary.
Net charge	the overall charge once positive and negative charges are added together.
Electric field	the region around a charge where another charge experiences a force.
Insulator	a material in which electrons cannot move freely, so charge stays in place.
Conductor	a material in which charge can move freely.
Neutral	having no net charge.