Static electricity

Question 1

What happens when two oppositely charged objects are brought near to each other

Answer 1

They will pull towards each other

Question 2

What happens when two similarly charged objects are brought near to each other

Answer 2

They will push away, repel.

Question 3

What does the strength of the pull or push depend on?

Answer 3

How close the two objects are. The strength increases as the objects are closer together.

Question 4

What’s one way to remove electrons from atoms

Answer 4

rub the object made of the atoms.

eg if glass is rubbed by a piece of silk cloth, the electrons can be rubbed off the atoms of the glass and onto the cloth. The glass loses electrons so becomes positively charged. The cloth gains electrons and so becomes negatively charged.

Question 5

What is charging by friction

Answer 5

When charging happens by rubbing. When a material is charged by friction (as e- are rubbed off from one thing and on to the other) the result is always that one thing gains a positive charge and the other gains a negative charge.

Question 6

What does charging by friction involve

Answer 6

The transfer of electrons.

Question 7

What is the difference between a conductor and an insulator

Answer 7

A conductor allows e- to freely flow through the substance. An insulator does not allow e- to flow easily through the material.

Question 8

What happens when a conductor becomes negatively charged

Answer 8

The e- rubbed onto its surface are all close together, so they will repel one another and move away from one another so the negative charge spreads out around the conductor. The added e- stay around the surface of the conductor. This is because the total push from the other added e- will push the e- towards the surface. So ALL e- move towards the surface of the conductor.

Question 9

What happens when a conductor becomes positively charged

Answer 9

E- from inside the material are attracted towards the positively charged surface. They take place of the e- that have been rubbed off, making those atoms neutral again. But they leave the atoms with missing e- inside the material so the + charge is spread out out the surface of the conductor.

Question 10

What happens when an insulator becomes negatively charged

Answer 10

Even though the added e- are close together and try to repel, they stay in approx the same place because their movement is restricted. They are not able to spread out so charge stays where it was originally put.

Question 11

What happens when an insulator becomes positively charged

Answer 11

If e- are rubbed off, the positively charged edge still tries to attract e- from within the material, but they cannot move to the edge so the edge stays positively charged.

Question 12

How quickly do charged objects lose their charge

Answer 12

If the charged object is a conductor, it will lose charge quickly. If the charged object is touching anything that also allows charge to flow easily (eg the hand of the person who is holding the charged object), the e- will flow and the charged object will again become neutral. This is why conducting objects usually lose their charge as soon as they get it.

If the charged object is an insulator, the most common reason that charge is lost is because of the moisture in the air. Water is a good conductor so water vapour in contact with the charged surface of an insulator allows e- to flow and eventually all the charge will be lost. The more moisture in the air, the quicker the charge will be lost.

Question 13

How are + and - charge in an uncharged object distributed?

Answer 13

Its equal quantities of positive charge and negative charge are uniformly distributed throughout.

Question 14

What happens if a positively charged rod is brought close to a neutral object?

Answer 14

the - charge e- in the neutral object are attracted to the +vely charged rod and move towards the rod, causing a non-uniform distribution of charge.

The top of the object becomes negatively charged because there are more e- at the top than before. The bottom of object becomes positively charged, because there are fewer e- at the bottom than before. The middle remains neutral, because e- that move up towards the top are replaced by the e- that have moved up from the bottom. The distribution of charge within the neutral object is NON-UNIFORM

Question 15

What does the strength of the charge at the top and bottom of a NON-UNIFORM distribution of charge object depend on?

Answer 15

Whether the object is made from conducting or insulating material. In a conductor the e- can move far more freely than in an insulator. So more charges would be at the bottom and top in a conductor than an insulator.

Question 16

What is charging by contact?

Answer 16

when a charged object comes into contact with an uncharged object, providing e- can flow relatively easily, charge can be transferred from the charged object to the uncharged object so that the uncharged object can become charged.

Question 17

Charging by contact when the charged object is positive

Answer 17

E- are drawn towards the positive charge and when contact is made, e- are transferred onto the positively charged object. When contact is broken, e- that have transferred across cannot get back and so the uncharged object is left with fewer e- than it had, so it gains a positive charge.

Question 18

The type of charge gained by the uncharged object is always the same as the type of charge on the charged object

Answer 18

True.

Question 19

What does the quantity of charge that is transferred across from charged object to uncharged object depend on?

Answer 19

How good as conductors the materials of the charged and uncharged objects are.

Question 20

If an object is charged and the e- have SOME ability to move, how does charge spread out?

Answer 20

The shape of the charged object affects the way the charges spread out. Charge will gather on any part of an object that is POINTED.

Question 21

Why does charge gather on a pointed part of an object?

Answer 21

Because each electron is being pushed by all the electrons on the either side of it. See diagram 62

If the object is positively charged, the electrons are all being pulled by the positive charge, however it will get more pull from the positive charges from the non-pointe end because there are more positive charges. So the e- will move towards the non-pointed end. The same thing will happen to other e- in the point, and so there will be a movement of e- out of the point, giving the point a stronger positive charge.

Question 22

What is an electrical discharge

Answer 22

When two oppositely charged objects are close to each other the strength of the attraction the the e- to the positive charge in the other object can become so great that the e- flow across the gap between the two objects.

Question 23

What is an electrical discharge often accompanied by? (observations)

Answer 23

Crackling sound, sometimes a spark can be seen to jump across the gap.

Question 24

Why does electrical discharges sometimes happen when a neutral object is charged by contact with a charged object?

Answer 24

As the two objects approach each other, the charged object will affect the charge distribution in the neutral object so that part of the neutral object closest to the charged object will have the opposite charge. Just before the two objects touch, the positive charge on one object is very close to the neg charge on the other. The electrons don’t wait for contact to be made, but flow across the air gap.

Question 25

What is an example of discharge flying through the air

Answer 25

Lightning

Question 26

How does lightning work

Answer 26

A thundercloud consists of huge quantities of water and ice droplets moved around by strong currents within a cloud. One theory is that the rubbing of these droplets against one another and against the air causes charging by friction. The result is a cloud that has a positive charge accumulated at the top of the cloud, negative charge at the bottom. The pos charged particles are lighter so rise to the top of the cloud, and vice versa.

The neg charge at the bottom of the cloud pushes the e- in the ground deeper below the surface, leaving the pos charge at the surface. The strength of this positive charge can get so great that e- pour of the cloud down to the ground. This is LIGHTNING.

Question 27

Situations where a discharge can be dangerous

Answer 27

The human body is a reasonably good conductor and so if a discharge flows towards someone, e- can pass through their body fairly easily. E- flowing through a body (an electric shock) can cause a lot of damage to the body.

A discharge can create a lot of heat. Heat can cause fires and explosions, which can be very dangerous.

Question 28

Why do steps need to be taken to stop the discharge being produced

Answer 28

If the production of a discharge could cause danger.

Question 29

What is an important property of the ground below Earth’s surface?

Answer 29

It is a good conductor of electrons. Because the Earth is so huge, large quantities of e- can pour into or out of the ground without significantly affecting its overall neutral charge.

Question 30

What is earthing

Answer 30

Channeling charge down to the ground. If the e- that would have jumped across a gap, causing a dangerous discharge, can be conducted down to the ground instead, a discharge will not be produced and any danger will be avoided.