Topic 11 - Static Electricity Flashcards
How can an insulator be charged by friction?
When insulating materials rub against each other, they may become electrically charged. Electrons, which are negatively charged, may be ‘rubbed off’ one material and on to the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with a positive charge.
What do like charges do and what do unlike charge do?
Two things with the same charges repel and two thing with different charges attract
Name some everyday situations of static electricity. (3)
- Shocks from everyday objects
- Lightning
- Attraction by induction such as a charged balloon attracted to a wall.
How is static electricity involved in lightning?
As particles of water/ ice move about in the cloud - friction causes the bottom of the cloud to become negatively charged. The ground also becomes charged making a spark even more likely. The neutral ground becomes positively charged because the negatively charged bottom of the cloud repels the electrons in the ground making surface positive creating an induced charge. The lightning strikes from the cloud to release the extra electrons and this spark earths the large charge.
How is the balloon able to stick on the wall with charge?
When you rub the balloon on a jumper, the electrons in the jumper transfer to the balloon making the jumper positively charged and the balloon negatively charged due to friction. When you bring the balloon near the neutral wall, the electrons in the wall move towards the opposite side of the wall as like charges repel. This means that one side temporarily becomes positively charge and the other negatively charged. This is means that the negatively charged balloon can stick onto the positively charged side.
What does earthing do?
It provides an easy route for the static charge to travel into the ground. This means that no charge can build up to give you a shock or make a spark. The electrons flow down the conductor to the ground if the charge is negative and flow up the conductor from the ground if the charge is positive. Fuel tankers must be earthed to prevent any sparks that might cause the fuel to explode.
What are some uses of electrostatic charges in everyday situations?
Insecticide sprayers and paint sprayers. The spray gun is charged, which charges up the small drops of paint. Each paint drop repels all the others, since they’ve all got the same charge, so you get a very fine even spray The object to be painted is given an opposite charge to the gun. This attracts the fine spray of paint. This method gives an even coat and hardly any paint is wasted. In addition, parts of the bicycle or car pointing away from the spray gun still receive paint, i.e. there are no paint shadows. Insecticide sprayers work in similar way, except the crops to be sprayed aren’t given opposite charge - the plants charge by induction as the insecticide droplets come near them
What are some of the dangers of sparking in everyday situations? How could they be prevented? (3)
> Refuelling cars - as fuel flows out of a filler pipe then static can build up. This can easily lead to a spark which might cause an explosion.
Static on planes - as planes fly through the air, friction between the air and the plane cause the plane to become charged. This build up of charge can interfere with communications equipment.
Lightning - The huge spark from the cloud to the ground could cause damage to homes or start fires when it strikes the ground.
These could be prevented by earthing
What is an electric field?
The region where an electric charge experiences a force.
In what direction to field lines point in?
Positive to negative
What are field lines like in a positive and negative radial field?
In a radial field around a positive charge, other positive charges are repelled away. Therefore, the arrows point away from the central positive charge. This is what happens with a Van de Graaff generator.
However, a negative charge placed in that field would attract the positive charge and feel a force in the opposite direction to the field lines.
What are the field lines like between two parallel plates?
It creates a uniform field a one plate is positive and the other is negative. The strength and direction of the field is the same anywhere between the two plates.
How do electric fields help to explain sparking by static electricity?
When an object becomes statically charged, it generates its own electric field. Interactions between this field and other objects are the cause of events like sparking. For example, a comb after it’s been run through your hair, it’s charged and so produces an electric field. This electric field interacts with the pieces of paper (without touching them) and so they feel a force. This force causes them to move towards the comb (and some will even stick to it). Sparks are caused when there is a high enough potential difference between a charged object and the earth (or an earthed object). A high potential difference causes a strong electric field between the charged object and the earthed object. The strong electric field causes electrons in the air particles to be removed (known as ionisation). Air is normally an insulator, but when it is ionised it is much more conductive, so a current can flow through it. This is the spark
