SP11 Static Electricity

Question 1

What is charging by friction?

Answer 1

When certain insulating materials are rubbed against each other they become electrically charged

Question 2

Explain why, when certain materials are rubbed
together, they end up with opposite charges

Answer 2

• Negatively charged electrons are transferred from one material to the other
• since the electrons are negatively charged, the material losing the electrons becomes positively charged, whilst the one gaining the electrons becomes negatively charged

Question 3

Explain how attraction by induction occurs

Answer 3

By rubbing the two materials together, they gain opposite charges. This difference in charges leads to a force of attraction between itself and other objects which are also electrically neutral, by attracting the opposite charge to the surface of the objects they are attracted to

Question 4

When does a static electric shock occur?

Answer 4

• two objects are charged by friction
• they become oppositely charged
• the large surplus of electrons causes them to jump across an object that is neutral

Question 5

Define earthing

Answer 5

The process of removing excess charge by the movement of electrons

Question 6

When is earthing used?

Answer 6

When an object or a body is charged and the charge needs to be removed to avoid sparking

Question 7

How is earthing carried out?

Answer 7

By connecting the charged object to the Earth using a conductor

Question 8

How does lightning occur?

Answer 8

1. In a storm, clouds move over each other. This causes them to become charged when electrons are transferred between them
2. Since the ground is neutral, the negative charges from the cloud jump to meet the positive charges on the ground, creating a giant spark
3. This phenomenon is called lightning

Question 9

What are the uses of stattic electricity?

Answer 9

• photocopiers
• inkjet printers
• insecticide sprayers

Question 10

How is static electricity used in sprayers?

Answer 10

1. The liquid in the sprayer is given an electrostatic charge when it leaves the sprayer
2. This results in all of the particles repelling each other, which ensures that the spray remains fine and covers a large area
3. They are also attracted to the negative charges of the earth, so they will fall quickly and are less likely to be blown away

Question 11

What are the dangers of static electricity?

Answer 11

• sparking
• which could pose the rick of electrocution
• and the risk of a fire or explosion of any nearby flammable substances

Question 12

How can static electricity be a danger whilst fueling aircraft?

Answer 12

• fuel runs through the pipes at a very fast rate, which is very flammable
• friction betwween the fuel and the pipe causes the fuel to gain a charge
• if this charge were to cause a spark, the fuel could ignite and cause an explosion

Question 13

How can we avoid a spark building up when fuelling aircraft?

Answer 13

• The fuel tank is connected to the Earth using a bonding wire made of copper during the refuelling
• The conductor earths the plane by carrying the charge through to the earth which removes the risk of any sparks

Question 14

Define electric field

Answer 14

A region where an electric charge experiences a force

Question 15

How is the direction of an electric field determined?

Answer 15

On whether the charges are the same or not:
- if the charges of the field and the object are the same, the second object will move away from the charge creating the field because the force will be repulsive
- if the charges of the field and the object are opposites, the force will be attractive and the object will move towards the charge creating the field

Question 16

What does the size of the force depend on?

Answer 16

The strength of the field at that point

Question 17

When does the force of the field become stronger?

Answer 17

As the distance between the two charged objects decreases

Question 18

When does the force of the field become weaker?

Answer 18

As the distance between the two charged objects increases

Question 19

When do field lines point away from the charged object?

Answer 19

When the charged object carries a positive charge

Question 20

When do field lines point towards a charged object?

Answer 20

When the charged object carries a negative charge

Question 21

What do field lines show?

Answer 21

• where the field is the strongest
• the direction of the force on a charge in the field

Question 22

What is the electric field between two parallel plates called?

Answer 22

Uniform electric field

Question 23

Describe the field lines in a uniform electric field

Answer 23

• directed from the positive to the negative plate
• parallel
• straight lines

Question 24

What is the strength of the electric field determined by?

Answer 24

The space between the field lines:
- stronger field = closer field lines
- weaker field = field lines further apart