Static Electricity & Electric Circuits

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Energy and Change Static Electricity & Electric Circuits From sparks and lightning to simple circuits

Have you ever felt a small shock when you touched something, or watched lightning in a storm? Both are caused by electric charge.

In this lesson you will learn:

• what static electricity is, and where it builds up
• about positive and negative charges
• how rubbing moves electrons from one object to another
• why charges attract or repel each other
• how lightning happens, and how to stay safe in a lightning storm
• what an electric circuit is, and how to draw one with symbols
• the difference between an open and a closed circuit
• which materials are conductors and which are insulators

There are quick checks along the way. Try each one before you move on.

1. Static Electricity

Static electricity the build-up of electric charge on the surface of an object

Static electricity is the build-up of electric charge on the surface of an object.

The charge collects on the outside of the object. In this lesson you will see where the charge comes from, and what happens when it moves.

Stationary The charge stays where it is. It does not flow. Builds up on insulators Charges cannot flow away through an insulator, so they collect on its surface.

The word static means not moving. The charge is stationary: it stays where it is and does not flow.

Static charge builds up on insulators. An insulator is a material that does not allow electric current to pass through it, so the charge cannot flow away. You will learn more about insulators at the end of this lesson.

Static electricity: charge built up on a surface Static: it does not flow It builds up on insulators

Remember:

• Static electricity is the build-up of electric charge on the surface of an object.
• The charge is stationary: it stays where it is and does not flow.
• Static charge builds up on insulators, because charges cannot flow away through an insulator.

2. Charges

Proton carries a positive charge (+) Electron carries a negative charge (−)

There are two kinds of electric charge: positive (+) and negative (−).

• Protons carry a positive (+) charge.
• Electrons carry a negative (−) charge.

In the diagrams in this lesson, a + sign stands for a positive charge and a − sign stands for a negative charge.

A neutral (uncharged) object has equal numbers of positive and negative charges. They balance out, so the object has no overall charge.

An object with more + than − is positively charged. An object with more − than + is negatively charged.

Protons: positive (+) Electrons: negative (−) Neutral: equal numbers of + and −

Remember:

• Protons carry a positive (+) charge.
• Electrons carry a negative (−) charge.
• A neutral object has equal numbers of positive and negative charges.

3. Friction

Rub two objects together this is friction Electrons move from one object to the other Both objects are now charged

When two objects are rubbed together, friction transfers electrons from one object to the other.

Only electrons move. Protons do not move from one object to another.

Gains electrons becomes negatively charged Loses electrons becomes positively charged

Electrons carry a negative charge, so:

• A neutral object that gains electrons now has more negative than positive charge. It becomes negatively charged.
• A neutral object that loses electrons now has more positive than negative charge. It becomes positively charged.

The protons stay where they are. Only the number of electrons changes.

A rod is rubbed with a cloth. In this example, electrons move from the rod onto the cloth.

• Before rubbing, both objects are neutral: each has equal numbers of + and −.
• The rod loses electrons, so it becomes positively charged.
• The cloth gains those electrons, so it becomes negatively charged.
• Count the + signs: the protons have not moved.

Which object gains the electrons depends on the two materials that are rubbed together.

Plastic Perspex Glass Nylon Wool Silk

Materials such as plastic, perspex, glass, nylon, wool and silk charge easily when they are rubbed.

The charge stays on the surface of the rubbed object: this is static electricity.

Rubbing (friction) transfers electrons Only electrons move Gain electrons: negative Lose electrons: positive

Remember:

• Rubbing two objects together (friction) transfers electrons from one object to the other.
• Only electrons move. Protons do not move from one object to another.
• An object that gains electrons becomes negatively charged.
• An object that loses electrons becomes positively charged.

4. Attract and Repel

Charged objects push or pull on each other:

• Unlike (opposite) charges attract: + and − pull towards each other.
• Like charges repel: + and + push each other away.
• − and − also repel.

Unlike charges + and − attract Like charges + and + repel − and − repel

Like means the same, and unlike means opposite.

• Two positive charges are like charges, so they repel.
• Two negative charges are like charges, so they repel.
• A positive and a negative charge are unlike charges, so they attract.

Try this activity:

• Tear some paper into small pieces.
• Rub a plastic ruler (or a perspex ruler) with a cloth.
• Hold the rubbed ruler just above the small pieces of paper.

The charged ruler picks up the small pieces of paper: it attracts them.

Unlike charges attract Like charges repel + and − attract + and + repel, − and − repel A charged ruler picks up paper

Remember:

• Unlike (opposite) charges attract: + and − attract.
• Like charges repel: + and + repel, and − and − repel.
• A charged plastic or perspex ruler picks up small pieces of paper.

5. Discharge and Lightning

Charge builds up on an object The charge suddenly moves electrons jump We see a spark or feel a small shock

Sometimes built-up charge suddenly moves: electrons jump. This is called a discharge. We see it as a spark or feel it as a small shock.

Sparks and shocks from static electricity happen especially when the air is dry.

Lightning is a very large electrical discharge in the atmosphere.

Inside a storm cloud, charges build up in different parts of the cloud: positive near the top and negative near the bottom. When the charge difference becomes large enough, a discharge occurs, and we see it as lightning.

Water droplets and ice particles move around inside a storm cloud They collide with one another This causes electric charges to separate Charges build up in different parts of the cloud (positive near the top, negative near the bottom) When the charge difference becomes large enough, an electric discharge occurs We see the discharge as lightning

Read the steps on the board from top to bottom:

• Water droplets and ice particles move around inside a storm cloud and collide.
• The collisions make the electric charges separate.
• The charges build up in different parts of the cloud.
• When the charge difference is large enough, a discharge occurs: lightning.

Discharge: a spark or a small shock Especially when the air is dry Lightning: a very large discharge in the atmosphere Storm cloud: + near the top, − near the bottom

Remember:

• A discharge is when built-up charge suddenly moves (electrons jump). We see or feel it as a spark or a small shock, especially when the air is dry.
• Lightning is a very large electrical discharge in the atmosphere.
• In a storm cloud, water droplets and ice particles collide, the charges separate and build up (positive near the top, negative near the bottom), and when the charge difference is large enough, a discharge occurs: lightning.

6. Lightning Safety

Stay inside a building Avoid open fields Do not stand under an isolated tree Stay away from water Avoid unnecessary contact with electrical equipment

Lightning is dangerous. During a lightning storm:

• Stay inside a building.
• Avoid open fields.
• Do not stand under an isolated tree.
• Stay away from water.
• Avoid unnecessary contact with electrical equipment.

Caught outside when a lightning storm starts?

Use the safety measures to decide what to do:

• An open field: avoid it.
• An isolated tree: do not stand under it.
• Water: stay away from it.
• Electrical equipment: avoid unnecessary contact with it.
• The safe choice: go inside a building.

Stay inside a building Avoid open fields Do not stand under an isolated tree Stay away from water Avoid unnecessary contact with electrical equipment

Remember, during a lightning storm:

• Stay inside a building.
• Avoid open fields.
• Do not stand under an isolated tree.
• Stay away from water.
• Avoid unnecessary contact with electrical equipment.

7. Electric Circuits

An electric circuit is a complete path through which electric current can flow.

An electric current is the flow of charges along a conductor. (Static charge stays where it is. In a circuit, the charges flow.)

A simple circuit has:

• a cell or a battery
• wires
• a switch
• a device such as a bulb

The diagram uses circuit symbols. You will learn them in the next steps.

Circuit symbols Symbol Component Circuit symbol for a bulb: a circle with a cross inside it Bulb A circle with a cross inside it. Circuit symbol for a cell: a long line (positive) and a short line (negative) Cell Two parallel lines. The long line is the positive (+) terminal and the short line is the negative (−) terminal. Circuit symbol for a battery: two cells joined, positive of one to negative of the next Battery Two or more cells joined together: the + of one cell to the − of the next.

Circuit diagrams use symbols instead of pictures:

• Bulb: a circle with a cross inside it.
• Cell: two parallel lines. The long line is the positive (+) terminal and the short line is the negative (−) terminal.
• Battery: two or more cells joined together, the + of one cell to the − of the next.

Circuit symbols Symbol Component Circuit symbol for a closed switch: the lever touches the contact Switch (closed) The lever touches the contact. The path is complete. Circuit symbol for an open switch: the lever is lifted, leaving a gap Switch (open) The lever is lifted. There is a gap. Circuit symbol for a wire: a straight line Wire A straight line.

A switch opens and closes the path:

• Closed switch: the lever touches the contact. The path is complete.
• Open switch: the lever is lifted. There is a gap.
• Wire: a straight line.

All six circuit symbols Symbol Component Circuit symbol for a bulb: a circle with a cross inside it Bulb A circle with a cross inside it. Circuit symbol for a cell: a long line (positive) and a short line (negative) Cell Two parallel lines. The long line is the positive (+) terminal and the short line is the negative (−) terminal. Circuit symbol for a battery: two cells joined, positive of one to negative of the next Battery Two or more cells joined together: the + of one cell to the − of the next. Circuit symbol for a closed switch: the lever touches the contact Switch (closed) The lever touches the contact. The path is complete. Circuit symbol for an open switch: the lever is lifted, leaving a gap Switch (open) The lever is lifted. There is a gap. Circuit symbol for a wire: a straight line Wire A straight line.

Remember:

• An electric circuit is a complete path through which electric current can flow.
• An electric current is the flow of charges along a conductor.
• A simple circuit has a cell or battery, wires, a switch and a device such as a bulb.
• In the cell symbol, the long line is the positive (+) terminal.

8. Open and Closed

In a closed circuit, the switch is closed and there are no breaks in the path.

Current flows all the way around the circuit, so the bulb lights.

Now the switch is open: the lever is lifted, and there is a gap in the path.

This is an open circuit. Current will not flow, so the bulb does not light.

Here the switch is closed, but one of the wires is broken. There is a break in the path, so current won't flow and the bulb does not light.

A break in the path makes an open circuit too, even when the switch is closed.

Closed circuit The switch is closed and there are no breaks. Current flows and the bulb lights. Open circuit The switch is open, or there is a break in the path. Current will not flow and the bulb does not light.

Remember:

• A closed circuit has the switch closed and no breaks: current flows and the bulb lights.
• An open circuit has an open switch or a break in the path: current will not flow and the bulb does not light.

9. Conductors and Insulators

Conductor a material that allows electric current to pass through it Metals such as copper Tap water

A conductor is a material that allows electric current to pass through it. Examples:

• metals such as copper
• tap water, because of the substances dissolved in it

The wires in a circuit are usually made of copper, because copper is a conductor.

Insulator a material that does not allow electric current to pass through it Rubber Plastic Fabric

An insulator is a material that does not allow electric current to pass through it. Examples: rubber, plastic and fabric.

Remember from the start of the lesson: static charge builds up on insulators, because charges cannot flow away through them.

An electrical cable uses both kinds of material:

• The wire inside is copper, a conductor, so current flows along it.
• The cover is plastic, an insulator, so the current stays inside the copper wire and cannot pass through the cover.

Conductors Allow electric current to pass through them. Metals such as copper; tap water (because of the substances dissolved in it). Insulators Do not allow electric current to pass through them. Rubber, plastic and fabric.

Remember:

• A conductor is a material that allows electric current to pass through it: metals such as copper, and tap water (because of the substances dissolved in it).
• An insulator is a material that does not allow electric current to pass through it: rubber, plastic and fabric.
• A cable has a copper wire (conductor) inside a plastic cover (insulator).

Static electricity: charge built up on a surface Protons +, electrons −; rubbing moves electrons Unlike charges attract, like charges repel Lightning: a very large discharge A circuit is a complete path for current Conductors let current through; insulators do not

Static Electricity & Electric Circuits: full summary

• Static electricity is the build-up of electric charge on the surface of an object. The charge is stationary (it does not flow), and it builds up on insulators.
• Protons carry a positive (+) charge and electrons a negative (−) charge. A neutral object has equal numbers of each.
• Rubbing (friction) transfers electrons from one object to the other. Only electrons move. Gain electrons: negative. Lose electrons: positive.
• Unlike charges attract; like charges repel. A charged plastic or perspex ruler picks up small pieces of paper.
• A discharge is a spark or a small shock, especially in dry air. Lightning is a very large electrical discharge in the atmosphere.
• Lightning safety: stay inside a building; avoid open fields; do not stand under an isolated tree; stay away from water; avoid unnecessary contact with electrical equipment.
• An electric circuit is a complete path through which current (the flow of charges along a conductor) can flow. In the cell symbol, the long line is +.
• A closed circuit (switch closed, no breaks) lets current flow and the bulb lights. An open circuit (open switch or a break) stops the current.
• Conductors: metals such as copper, and tap water (because of the substances dissolved in it). Insulators: rubber, plastic and fabric.

You are ready for the quiz.