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• An electrical charge is created when electrons are transferred to or removed from an object. Because electrons have a negative charge, when they are added to an object, it becomes negatively charged. When electrons are removed from an object, it becomes positively charged.

Rights: Peter Terren

Seeing electricity

Using junk and materials from hardware shops, Peter Terren carries out amazing experiments with a Tesla coil – a machine (transformer) that turns electricity into streams or sparks that fire directly into the air or strike nearby objects like lightning.

## What is an electrical charge?

An electrical charge is created when two materials come into contact or are rubbed together. When the materials are in contact, electrons can be literally rubbed off of one object and onto the other. This doesn’t mean that any two materials rubbed together will cause electrons to move. Some materials are much more willing to donate electrons, and others are much more likely to accept electrons. A list of materials ordered by their ability to donate electrons is called a triboelectric series.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Triboelectric series

The triboelectric series shows the static electric potential of common materials. Materials towards the positive end give up electrons when brought into contact with materials towards the negative end.

Most of us have probably all generated a static electrical charge at some point in time. The shock you receive when you walk across a carpet and touch a metal surface or when you feel the cling of statically charged clothing are evidence of a static electrical charge.

Hair and rabbit’s fur give up electrons easily, whereas polyethylene and Teflon are good at attracting electrons. When two materials in different positions on the triboelectric series are rubbed together, the materials towards the positive end give up electrons and become positively charged, and those towards the negative end accept electrons and become negatively charged.

## How do you create an electrical charge?

Consider a practical example of creating an electrical charge. When a balloon is rubbed on hair, electrons are moved from the hair to the surface of the balloon. The electrons ‘stick’ to the balloon where the balloon was rubbed and do not move across the surface of the balloon. The balloon becomes negatively charged (red electrons), and the person’s hair becomes positively charged (fewer electrons than before).

Rights: The University of Waikato Te Whare Wānanga o Waikato

Moving electrons

When a balloon is rubbed on hair, fur or wool, electrons are moved from the hair to the balloon, giving the balloon a negative charge.

Now let’s use the newly charged balloon to charge another balloon. When we touch the charged balloon to a neutral (balanced – no extra electrons) balloon, some of the added electrons are transferred to the neutral balloon. Now both balloons have a negative charge, and we notice something – the balloons push apart. The charge on the balloons causes a force that pushes the balloons apart. The force is much like the repulsive force you feel when you bring two magnets together north to north or south to south.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Charging a balloon by contact

Electrons are transferred from a charged balloon to a neutral balloon by contact, leaving both balloons negatively charged.

## Insulators and conductors

Insulators are materials such as glass, rubber, wood and most plastics where the electrons are held quite tightly and are not free to move easily from place to place. Conductors are materials such as copper, silver, gold and iron where electrons are free to move from place to place.

For example, a charged balloon (insulator) is brought near a neutral aluminium can (conductor). While the can is far away from the balloon, the negative charge on the balloon has little or no effect on the can, and the electrons on the can are evenly dispersed. When the balloon is brought near the can, something interesting happens – the electrons move to the side of the can to get as far away from the negatively charged balloon as possible. This leaves the side of the can nearest the balloon positively charged. The can as a whole is still neutral, but because the positively charged side of the can is close to the balloon, the negative charges on the balloon attract the positive side of the can and the force pulls the balloon and can together. If the can is lying on its side, it will roll towards the balloon.

Rights: The University of Waikato Te Whare Wānanga o Waikato

A charged balloon is attracted to a neutral conducting can

When a charged balloon is brought near a conductor, the electrons in the conductor move away from the balloon, causing an attraction.

Something quite different happens if the conducting can is allowed to touch the charged balloon. When the balloon and can touch, some of the electrons on the balloon will flow onto the can, leaving the can with extra electrons and therefore negatively charged. Now both the balloon and can are negatively charged, and the like charges cause a force pushing the can and balloon apart. If the can is lying on its side, it will roll away the balloon.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Charging a conducting can by contact with a balloon

When a charged balloon is brought into contact with a neutral can, electrons from the balloon move to the can, leaving the can negatively charged. The balloon and can repel each other.

## Induction

In the above example, we used a negatively charged balloon to impart a negative charge to the can by a process of direct contact. It is also possible to use a negatively charged balloon to impart a positive charge on a can through a process called induction.

If the balloon is brought near the can, the electrons move to the far side of the can, as described earlier. If another object, like a finger, now touches the negative side of the can, some of the overcrowded electrons will flow onto the object, leaving the can positively charged.

Rights: The University of Waikato Te Whare Wānanga o Waikato

Charging by induction

When a charged balloon is brought near a conducting can, the electrons are pushed to the far side of the can. If another object touches the side of the can opposite the balloon, electrons flow into the other object, leaving the can positively charged.

Thus it is possible to use a negatively charged balloon to impart either a negative charge (by contact with the balloon) or a positive charge (by induction).

## Nature of science

In science, a model is a representation of an idea, an object or even a process or a system that is used to describe and explain phenomena that cannot be experienced directly. Models are central to what scientists do, both in their research as well as when communicating their explanations.

## Related content

This article will help understand atomic structure and provides a simple model to explain the movement of electrons in conductors and insulators.

Find out how to make a simple electromagnet in this activity.

This activity supports students to construct simple electrical circuits and test a variety of materials to identify those that are good conductors and those that do not conduct electricity.

This recorded professional learning session will build your confidence to teach Physical World.

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