Chapter 3: Static Electricity Flashcards
What happens when you rub two different insulators together?
They gain a charge, and attract each other.
What is the law of electrostatics?
Like charges repel, and opposite charges attract.
What happens when you have a large static charge?
The greater the static charge stored, the greater the potential difference between it and the Earth
How is a spark produced?
If the potential difference becomes high enough, it can discharge, causing the air to conduct and produce a spark.
Describe an experiment to demonstrate the law of electrostatics.
We rubbed cloth against two different plastics to remove/give them electrons, changing the charge. We noticed that when the two different plastics were put together, they attracted, however when two of the same plastic were put together, they repelled.
Describe how to reduce the risk of sparks when refuelling an aeroplane.
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 produced, which in turn can cause an explosion. Therefore, when refuelling aeroplanes, an earthed wire is attached to the plane and the fuel tank, allowing the excess charge to come down into the Earth.
Describe how to reduce the risk of sparks in operating theatres?
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 occur, there would be a massive explosion 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.
How does an object gain a negative or positive charge?
Through the movement of electrons. Electrons are negative so when there are lots of them, the object has a negative charge, and when there are less of them, it has a positive charge.
How is an object given an induced charge when another charged object is brought close to it?
Through the law of electrostatics. The negative electrons are either attracted or repelled by the charge of the other object, inducing a charge in the previously neutral object.
Why can’t metals store a static charge, unless they are isolated?
Metals are conductors, and so they conduct the charge rather than storing it.
How is static electricity useful for spray painting?
The powder rubs against the barrel of the gun, and so each individual particle of paint becomes positively charged. They repel each other, and so the coat of pain is very smooth and even. The bike is given an induced charge, so any particles that miss the first side will be attracted to the other side of the bike. This means you don’t need to turn the bike around, and you waste less paint.
Explain how the photocopier works.
The image of the document is projected onto a positively charged copying plate. Where light falls on the plate, electrical charge leaks away. Negatively charged black toner particles are attracted to the remaining positive areas. Paper is placed over the copying plate; the toner is transferred to the paper and heated so that it sticks. The photocopy is taken off the copy plate and turned over to reveal the image.
Explain how the electrostatic precipitator works.
The friction between the dust and the positively charged grid causes the dust to gain a static charge. The dust particles repel each other. The earthed collecting plates gain an induced negative charge. The dust particles are attracted to the earthed collecting plates. The gas continues to rise up and out of the chimney.
