Exercises: Electrical nature of matter: charging by friction

We rub a balloon against a T-shirt and, when bringing it close to small pieces of paper, they jump and stick to the balloon, as shown in the diagram.

What is this method of charging an object by rubbing it called? Explain in your own words what has happened to the balloon.

How many types of electric charge are there and what are they called? Look at the two pairs of charges in the diagram:

Explain what happens when two charges of the same type are brought close together and what happens when two charges of different types are brought close together.

After combing his hair with a plastic comb, Cian brings it close to a thin stream of water from the tap and the water bends towards the comb, as shown in the diagram.

What happened to the comb when it was rubbed against his hair? Why is the water deflected towards it?

Atoms have positively charged protons, negatively charged electrons and uncharged neutrons. An atom has $6$ protons and $6$ electrons, like the one in the diagram.

1. a) What is its total charge?
2. b) What type of charge will the atom have if it loses an electron?

State which of these objects allow electric current to pass through well (conductors) and which do not (insulators): an iron key, a plastic ruler, a coin, an eraser, a steel spoon and a wooden toothpick.

Complete the sentence with the missing words: "An electric current is the movement of electric $\dots$ through a $\dots$, such as the copper in wires". Then explain the sentence in your own words.

In winter, when taking off her woollen hat, Vega's hair stands on end and some hairs stick to the hat. Why does her hair stand on end and why do individual hairs separate from each other? Explain this using what you know about charges.

The inside of cables is made of copper and the outer sheath is made of plastic, as seen in the cross-section in the diagram.

Why are they not made the other way round, with plastic on the inside and copper on the outside? Give reasons for your answer using the words conductor and insulator.

We rub two balloons with the same woollen cloth and bring them close to each other, as in the diagram.

1. a) Will they attract or repel each other?
2. b) Justify your answer by considering the type of charge each balloon has received.

Cian brings a rubbed plastic rod close to a small cork ball hanging from a thread, as shown in the diagram.

The small ball moves towards the rod and touches it; immediately afterwards, it flies backwards. Explain why the ball first moves closer and then moves away.

To find out if a material lets current pass through, we assemble a circuit with a battery, a light bulb and two loose wires, as in the diagram.

When touching a coin with the ends, the bulb lights up; when touching a wooden toothpick, it does not light up.

1. a) What do you conclude about each of the two materials?
2. b) What name is given to the materials in each group?

When rubbing a balloon against hair, some of the charge transfers from the hair to the balloon, and the balloon is left with a negative charge.

1. a) What type of charge is then left on the hair?
2. b) Explain why, when slowly pulling the balloon away, some hairs stretch out towards it.

Inside a storm cloud, water droplets and ice crystals rub against each other and the cloud builds up a huge amount of electric charge, as shown in the diagram.

Using these ideas, explain what has charged the cloud and why we say a lightning flash is like a giant spark.

We hang a small polystyrene ball from a thread. First we bring a finger close and nothing happens; then we bring a plastic ruler that has just been rubbed with a cloth close and the small ball moves towards the ruler.

1. a) Why does nothing happen with the finger?
2. b) Why does it move with the rubbed ruler?

When going down a plastic slide, your body rubs against the surface. When reaching the bottom and touching the metal handrail, we sometimes feel a small electric shock. Explain step by step, from when we start going down, how this electric shock is produced.

Sara rubs a balloon against the carpet and leaves it stuck to the ceiling, where it stays for a long time.

1. a) What is the charge on the balloon after rubbing?
2. b) After a few hours the balloon falls. What do you think happened to its charge?

Aoife rubs a balloon with a woollen cloth and checks that it attracts small pieces of paper.

1. a) Explain what has happened to the charges on the balloon and the cloth when rubbing them.
2. b) Why does the balloon now attract the pieces of paper?
3. c) If she rubs a second balloon with the same cloth and brings the two balloons close together, what will happen? Justify your answer.

Andrea says: "When rubbing a balloon, new charge is created that did not exist before." Bruno replies: "It is not created: charge transfers from one body to the other, which is why the balloon and the cloth end up with different charges."

1. a) Who is right?
2. b) Support your answer by considering what happens to the two objects being rubbed.

You want to test if a piece of chalk can be charged by friction, like a balloon.

1. a) Make a list of materials you would use.
2. b) Describe the experiment step by step.
3. c) What would you observe if the chalk becomes charged? And if it does not become charged?

Technicians repairing computers wear a wrist strap connected by a cable to a metal pipe, because a small shock of static electricity can damage the components.

1. a) How can a person's body become charged while working (clothes, shoes, chair)?
2. b) What would happen to that accumulated charge if they touch a delicate component?
3. c) Explain what the wrist strap does with the charge and why the cable ends at a piece of metal.

Charging experiments work much better on dry days than on humid days: a rubbed ruler that attracted pieces of paper in the morning hardly moves them on a rainy afternoon.

1. a) What happens to the charge on the ruler over time?
2. b) Knowing that water helps charge escape from objects, explain why on humid days the experiment works less effectively.

A plug has a hard plastic casing and metal pins, as shown in the diagram.

1. a) What electrical property is required in each of the two parts?
2. b) What would happen if the casing were made of metal?
3. c) What if the pins were made of plastic? Explain whether the plug would work.

When rubbing a glass rod with a silk cloth and bringing it close to another glass rod rubbed in the same way, they repel each other. But if we bring the rubbed glass rod close to a plastic rod rubbed with wool, they attract each other.

1. a) What do you conclude about the charges on the two glass rods?
2. b) And about the charges on the rubbed glass and plastic?
3. c) How many types of charge do you think exist? Give reasons for your answers using the rule of attraction and repulsion.

At a petrol station, before filling up with petrol, it is recommended to touch the metal bodywork of the car with your hand.

1. a) How might the driver's body have become charged during the journey?
2. b) What could happen if that charge jumped as a spark near petrol vapours?
3. c) Why does touching the bodywork beforehand prevent the danger?