Electric Charge: Answers

Explain what is meant by materials which are good conductors and materials which are good insulators. Give examples of each.

A material which is a good conductor is one in which electricity can pass through easily. Metallic materials such as copper, aluminium and iron are good conductors of heat and electricity so we use these elements to make things such as electrical wiring. An insulating material is one which does not allow electricity to pass through. Insulating materials include things like plastic, wood and wool. We use plastic as insulating cover around electric wires to prevent the user from an electric shock.

Morty rubs a balloon on his head and presses it to the wall. When he takes his hand away, the balloon stays stuck to the wall. Explain why this happens.

Rubbing two insulating materials together, such as hair and a balloon, generates friction. The friction causes electrons to be rubbed off Morty’s hair and transferred to the balloon. His head will now have a positive charge (because of the loss of electrons) while the balloon has a negative charge (it has gained electrons). When Morty places the balloon near the wall, electrons in the wall will be repelled by the balloon and will move away from the surface of the wall. This leaves the wall’s surface positively charged and able to attract the ball and hold it in position (since opposite charges attract).

Using ideas about static electricity, explain how lightning happens.

In a storm cloud, friction between ice particles and rain droplets causes the accumulation of electrons in the cloud. This creates a build-up of voltage and when the voltage becomes too high, the electrons will ‘jump’ to the ground and discharge the electricity. The movement of electrons from the cloud to the ground is seen as lightning.

Why is static electricity dangerous? What can be done to minimise the dangers?

Static electricity is dangerous because the increased voltage can result in a spark when the electrons ‘jump’ to the earth. The spark could start a fire and is a serious issue when refuelling airplanes (since friction between fuel and the pipes can cause static electricity). To reduce the risk of a fire, airplanes are connected to the earth with a metal rod to allow electrons to pass safely to the ground.

Give two uses of static electricity.

Static electricity is used for photocopying documents and for spray-painting cars or other objects. The image plate within a photocopier has a positive electrostatic charge. Any parts of the image that are blank will allow light to pass through and cause the positive charge to leak away, leaving only parts of the paper that contain ink to have a positive charge. These areas attract negatively charged particles of black powder which are pressed to the paper when it passes through heated rollers. For spray-painting cars, the paint is given a positive electrostatic charge which neatly covers the whole car since the positive paint particles repel each other, making it easy for paint to get into the nooks and crannies of the car without using excess paint, resulting in a smooth finish.