Topic 11 - Static electricity

Question 1

What happens when certain insulators are rubbed together?

Answer 1

negatively charged electrons are scraped off one and dumped on another. As these electrons are not free to move due to the materials being insulators, it results in a build up of charge - static electricity

Question 2

Which insulator has the positive static charge, the one that had lost electrons or the one that had gained electrons?

Answer 2

The one that had lost electrons.

Question 3

Which insulator has the equal but negative static charge, the one that had lost electrons, or the insulator that had gained electrons?

Answer 3

The insulator that gained electrons

Question 4

What materials could you use in an experiment to show static electricity?

Answer 4

Polythene and acetate rods being rubbed with a cloth duster

Question 5

Two things with opposite charges (attract/repel)?

Answer 5

attract

Question 6

two things with the same charges (attract/repel?

Answer 6

repel

Question 7

Describe induction with a balloon?

Answer 7

Rubbing a balloon against your hair, your hair transfers electrons to the balloon, leaving it with a negative charge. If you then hold a balloon against a wall, it will stick

Question 8

Why does the balloon stick onto the wall?

Answer 8

This is because the charges on the surface of the wall can move a little - the negative charges on the balloon repel the negative charges on the surface of the wall. This leaves a positive charge on the surface, which attracts the negatively charged balloon

Question 9

Describe induction with a comb

Answer 9

If you run a comb through your hair, electrons will be transferred to the comb, making it negatively charged. It can then be used to pick up little pieces of uncharged paper - holding it near the little pieces of paper makes them jump up and stick to the comb

Question 10

How can static/electric charge cause shocks?

Answer 10

1 - When an electric charge builds on an object, the pd between the object and the earth increases
2- If the pd gets large enough, electrons can jump across the gap between the charged object and the earth. This is the spark
3- they can also jump to any earthed conductor that is nearby e.g. why we get static shocks from clothes

Question 11

How do electrostatic paint sprayers (paints that work in the same way e.g. insecticide sprayers work?

Answer 11

1- The spray gun is charged, which charges up the small drops of paint. Each paint drop repels all the others, since they’ve got all the same charge, so you’ve got a very fine even spray
2- The object to be painted is given an opposite charge to the gun. This attracts the fine spray of paint.

Question 12

What is an advantage of electrostatic paint sprayers?

Answer 12

• gives an even coat of paint
• hardly any paint is wasted
• parts of an object pointing away from the spray gun still receive paint

Question 13

How can static electricity be dangerous when refueling cars?

Answer 13

As fuel flows out of a filler e.g. into an aircraft or tanker, then static can build up. This can easily lead to a spark, which might cause an explosion in dusty or fumey places e.g. a petrol station

Question 14

How can static electricity be dangerous on airplanes?

Answer 14

As planes fly though the air, friction between the air and the plane cause the plane to become charged. This build up of static charge can interfere with communication equipment

Question 15

What causes lightning?

Answer 15

Raindrops and ice bump together inside storm clouds, leaving the top of the cloud positively charged and the bottom of the cloud negatively charged. This creates a huge voltage and a big spark, which can damage homes or start fires

Question 16

What is earthing?

Answer 16

Connecting a charged object to the ground using a conductor

Question 17

How can earthing stop an electrostatic charge building up?

Answer 17

• Earthing provides an easy route for the static charge to travel into the ground. This means no charge can build up to give you an electric shock.
• 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

Question 18

Why must fuel tankers be earthed?

Answer 18

To prevent any sparks that might cause the fuel to explode

Question 19

What is an electric field?

Answer 19

It’s the region around a charge object where, if a second object was placed inside it, a force would be exerted on both of the objects

Question 20

Describe 3 features of electric field lines?

Answer 20

1. Electric field lines go from positive to negative
2. They’re always at a right angle to the surface
   3 The closer together the lines are, the stronger the field is

Question 21

Why may two objects be attracted to each other (in terms of field lines)?

Answer 21

The field lines between two oppositely charged objects point in the same direction, the field lines ‘join up’ and the objects are attracted to each other

Question 22

Why may two objects repel each other (in terms of field lines)

Answer 22

The field lines between two non-oppositely charged object point in opposite directions, the field lines ‘push against’ each other and the objects repel each other

Question 23

Does the strength and direction of the field change between the two plates or do they stay the same?

Answer 23

They stay the same anywhere between the two plates (its only different at the very ends)

Question 24

When drawing an electric field diagram, what must you include?

Answer 24

1. arrows on the field lines
2. Show at least 3 field lines
3. Make sure they’re parallel
4. Make sure the field lines are all the same distance apart

Question 25

When an object is statically charged, it generates its own…

Answer 25

Electric field

Question 26

Use the example of the comb to explain why paper may stick to a statically charged comb? (explain it using the idea of an electric field)

Answer 26

As the comb is charged, it produces an electric field. This electric field interacts with the piece of paper (without touching them) and so they feel a force. This force causes them to move towards the comb

Question 27

Explain how sparks can be explained by an electric field?

Answer 27

1. They are caused when there is a high enough pd between a charged object and the earth. A high pd causes a strong electric field between the charged object and the earthed object
2. This electric field causes electrons in air particles to be removed (ionised)
3. When air is ionised, it can carry a current. This is the spark