Static Electricity

Question 1

What is the law of electrostatics?

Answer 1

Like charges repel; opposite charges attract.

Question 2

What is the relationship between the static charge stored, and the potential difference between it and the earth?

Answer 2

The greater the static charge stored, the greater the potential difference between it and the earth.

Question 3

What causes a spark?

Answer 3

When an object has enough charge (high potential difference) it can discharge by causing the air to conduct and produce a spark.

Question 4

Describe an experiment to illustrate the law of electrostatics.

Answer 4

We rubbed cloth against the plastics to give them a static charge. We noticed that when the two different plastics were close to each other, they attracted, however when they were paired with the same type of plastic, they repelled.

Question 5

Explain the hazards of static electricity and how to reduce the chance of sparks and explosions when refuelling.

Answer 5

The fuel and the pipe will rub against each other, causing one to become negative and the other to become positive. If they get charged enough, a spark will be created, which in turn can cause an explosion. When refuelling aeroplanes, an earthed wire is attached to the plane, and the fuel tank which allows the excess charge to come down into Earth.

Question 6

Explain the hazards of static electricity and how to reduce the chance of sparks and explosions in an operating theatre.

Answer 6

Surgeons and doctors generate static electricity via their clothes, which are made of polyester, and the gases they use are often extremely flammable. If a spark were to cur, there would be a massive explosions, and kill at least three people. To prevent this, special conductive floors (which have metal fibres inside them) are used in operating theatres, so that every charge generated is immediately earthed.

Question 7

Explain how an object gains a negative charge by describing the motion of electrons.

Answer 7

The electrons will be moved to one side of the object (that side will be negative) or the object will have more electrons than protons.

Question 8

What happens when an insulator rubs against a different insulator?

Answer 8

The insulator will remove/give electrons to the other insulator, causing there to be a static charge

Question 9

Explain how an object gains a positive charge by describing the motion of electrons.

Answer 9

The electrons will move to one side of the object (the other side will be left positive) or the object will have less electrons than protons.

Question 10

What is induced charge?

Answer 10

When you charge up an object and then move it towards a neutral object, it will attract. This is called the induced charge.

Question 11

Explain the balloon experiment in terms of inducing charge

Answer 11

If a balloon is given a static charge, and put near a wall, they will attract because the electrons in the wall will move further away because they are repelled from the negative charge of the balloon. This leaves the surface of the wall positive, so because opposite charges attract, the balloon will be attracted to the wall.

Question 12

Explain why metals can’t store static charge unless they are isolated.

Answer 12

Metals conduct electricity, therefore unless they are isolated, the charge will flow away into another object, or the Earth.

Question 13

Explain how a negatively charged object becomes neutral through Earthing

Answer 13

When the negatively charged object touches the Earth, the excess electrons flow into the Earth, causing it to become neutrally charged

Question 14

Explain how a positively charged object becomes neutral through earthing

Answer 14

When the positively charged object touches the Earth, electrons from the Earth flow up into the object, causing it to become neutral.

Question 15

Explain what happens to the paint powder when it leaves the gun and how this affects the paintwork on the bike frame.

Answer 15

The powder rubs against the barrel of the gun, becoming positively charged. Like charges repel, so the coat of paint will be very smooth and even.

Question 16

The bike frame is earthed and therefore initially neutral in charge. Explain how the bike frame becomes negatively charged and what advantage this has over regular painting techniques.

Answer 16

Electrons from Earth are attracted to the positive powder, because opposite charges attract, so they travel up through the bike frame which then becomes negatively charged via induction. It takes less time because any paint that misses the bike will be attracted to the back of the bike, because opposite charges attract, which will therefore make the process quicker.

Question 17

An employee forgets to earth a bike frame. How will this affect the paint spraying process?

Answer 17

The electrons will move towards the powder because opposite charges attract, however eventually the bike will become positively charged due to the paint, and because like charges repel, the powder will repel from the bike.

Question 18

Explain what happens to the charged powder that initially misses the front side of the frame and how this is an advantage to the process

Answer 18

The charged powder that misses the front is attracted to the back of the bike as well, since the whole bike is negatively charged. This means that you don’t need to paint both sides, and you waste less paint.

Question 19

Explain how the electrostatic precipitator works

Answer 19

The friction between the dust and the positively charged grid causes the dust to gain a static positive charge. The dust particles repel each other because like charges repel. Due to the positive dust particles, the earthed collecting plates gain an induced negative charge because electrons from the Earth are attracted to the positive charge because opposite charges attract. The gas continues to rise up and out of the chimney.