Module 3.2 — Static Electricity and Conduction

What is static electricity?

The build-up of electric charge on an object.

What causes an object to become statically charged?

A transfer of electrons creates an imbalance of charge.

What are the two types of electric charge?

Positive (+) and negative (−).

How do two positive charges interact?

They repel each other.

How do two negative charges interact?

They repel each other.

How do opposite electric charges interact?

They attract each other.

Why is an ordinary atom electrically neutral?

It has equal numbers of protons and electrons.

What happens when an object loses electrons?

It becomes positively charged.

What happens when an object gains electrons?

It becomes negatively charged.

Which subatomic particles are transferred during ordinary static charging?

Electrons.

What happens to the total charge when electrons transfer between two isolated objects?

Charge is conserved; one gains what the other loses.

What happens when a static charge suddenly discharges?

Charge moves rapidly, potentially producing a spark or shock.

What natural phenomenon illustrates a large electrostatic discharge?

Lightning.

What is static cling?

Attraction between objects caused by electrostatic charges.

How can shuffling across a carpet produce static electricity?

Repeated contact and separation transfer electrons.

Why can touching an object after walking across carpet cause a shock?

Built-up static charge suddenly discharges.

What happens when a balloon is rubbed against hair?

Electrons transfer, leaving the balloon and hair oppositely charged.

What is the triboelectric effect?

Charge separation caused by electron transfer between contacting materials.

What happens to a material that loses electrons through the triboelectric effect?

It becomes positively charged.

What happens to a material that gains electrons through the triboelectric effect?

It becomes negatively charged.

Which electrons tend to transfer most easily during contact charging?

Weakly bound outer electrons.

What is the triboelectric series?

A ranking of materials by their tendency to become positively or negatively charged.

What happens when materials far apart in the triboelectric series contact and separate?

They generally develop a greater charge separation.

What charge does the higher material in the BA triboelectric series tend to acquire?

Positive relative to the lower material.

What charge does the lower material in the BA triboelectric series tend to acquire?

Negative relative to the higher material.

Which material is at the positive end of the BA triboelectric series?

Glass.

Which materials appear at the negative end of the BA triboelectric series?

Brass and silver.

In the BA series, which is more positive: glass or hard rubber?

Glass.

In the BA series, which is more negative: human hair or hard rubber?

Hard rubber.

In the BA series, which is more negative: cotton or silk?

Cotton.

In the BA series, which is more negative: copper or wool?

Copper.

What causes hair to stand up after contact charging?

Similarly charged hairs repel one another.

What is electrostatic induction?

Redistribution of charge caused by a nearby charged object.

Can a charged object attract an electrically neutral object?

Yes, by inducing separation of positive and negative charge.

Why can a neutral object be attracted to a charged object?

The closer induced opposite charge produces a stronger attraction.

Why is induced charge separation more pronounced in conductors?

Their mobile charges can redistribute more easily.

How does electrostatic force change as separation distance increases?

It decreases.

What is grounding or earthing?

Providing an electrical path for charge to move to or from Earth.

How can grounding an induced charge separation leave an object charged?

Electrons enter or leave while the grounding path is connected.

Which apparatus in the BA notes demonstrates electrostatic charge effects?

The Van de Graaff generator.

What is electrical conduction?

The movement of electric charge through a material.

What is an electrical conductor?

A material in which electric charges move relatively easily.

What is an electrical insulator?

A material in which electric charges move with difficulty.

Which class of materials commonly conducts electricity well?

Metals.

Name three metallic conductors identified in the BA notes.

Copper, silver and gold.

Why do metals generally conduct electricity well?

They contain mobile, loosely bound electrons.

What are free electrons?

Electrons able to move through a conducting material.

What happens when an atom loses an electron?

It becomes a positively charged ion.

What is a crystal lattice in the BA metallic model?

A regular arrangement of positive ions within a metal.

Which particles move freely through the metallic crystal lattice?

Free electrons.

Are the positive metal ions free to travel through the lattice?

No, they are held in regular lattice positions.

What do positive ions do at temperatures above absolute zero?

They vibrate around their lattice positions.

What are free electrons doing inside a metal above absolute zero?

Moving continually due to thermal energy.

Does random thermal motion alone produce a net electric current?

No, because the random motions have no overall direction.

Why can a metal remain electrically neutral despite having free electrons?

Its total positive and negative charges balance.

What can cause free electrons in a metal to develop a net directional flow?

An applied electric field or potential difference.

Toward which battery terminal are electrons attracted?

The positive terminal.

Why don't positive lattice ions travel toward the battery's negative terminal?

They are held in the crystal lattice.

What is conventional current direction in an external DC circuit?

From positive to negative.

What is electron-flow direction in an external DC circuit?

From negative to positive.

Why are conventional current and electron flow in opposite directions?

Electrons are negatively charged.

Which current direction was established before electrons were understood?

Conventional current.

Which direction represents actual electron movement in a metallic conductor?

Negative to positive.

Are conventional current and electron-flow conventions both used in industry?

Yes.

What is essential when using either current-flow convention?

Use the chosen direction consistently.

Does choosing conventional current instead of electron flow change circuit behaviour?

No; it changes the direction convention used to describe it.

What does DC stand for?

Direct Current.

What is the defining direction characteristic of DC?

Current flows in one direction.

Name three DC sources listed in the BA notes.

Batteries, solar panels and DC generators.

What is a polarity-conscious circuit?

A circuit that requires the correct supply polarity to operate properly.

Why must polarity be respected in some DC circuits?

Their operation depends on the supply's positive and negative connections.

What does AC stand for?

Alternating Current.

What is the defining direction characteristic of AC?

The current periodically reverses direction.

What does frequency describe in an AC supply?

The number of complete cycles per second.

What is the unit of electrical frequency?

Hertz (Hz).

What does an AC frequency of 50 Hz mean?

50 complete cycles occur each second.

Name two AC sources identified in the BA notes.

Inverters and AC generators (alternators).

What is a non-polarity-conscious load?

A load that can operate without a fixed positive and negative connection.

Name two examples of loads that may operate on either AC or DC.

Incandescent lamps and resistive heaters.

How can the presence of electric current be detected through light?

A lamp or LED produces light.

How can electric current be detected through heat?

A conducting element or electrical load becomes warm.

How can electric current be detected through magnetism?

Current produces a magnetic effect, as in an electromagnet or relay.

What chemical effect of electricity is identified in the BA notes?

Electrical current can produce chemical changes.

What pressure-related electrical effect is listed in the BA notes?

The piezoelectric effect.

What friction-related electrical effect is listed in the BA notes?

Static charge produced through contact and separation.

What sensation can indicate an electric current or discharge?

An electric shock.

What is the SI unit of electric charge?

The coulomb.

What symbol is used for the coulomb?

C.

What symbol is used for quantity of electric charge?

Q.

Approximately how many elementary electron charges equal one coulomb in magnitude?

6.25 × 10¹⁸.

Does the coulomb measure charge or the rate of charge flow?

The quantity of charge.

What is electric current?

The rate of flow of electric charge.

What symbol represents electric current?

I.

What is the SI unit of electric current?

The ampere (A).

What is one ampere equal to?

One coulomb of charge flowing per second.

What formula relates current, charge and time?

I = Q/t.

What does I represent in I = Q/t?

Current in amperes.

What does Q represent in I = Q/t?

Charge in coulombs.

What does t represent in I = Q/t?

Time in seconds.

What is the rearranged formula for total charge transferred?

Q = It.