P4 a-d

Question 1

Name two types of charge.

Answer 1

Positive and negative

Question 2

Like charges always…….

Answer 2

Like charges always repel, opposite charges attract.

Question 3

What charge do all electrons have?

Answer 3

Electrons are always negative.

There is no such thing as a positive electron!

Question 4

How can you get an electric shock?

Answer 4

If you touch something that is charged.

Question 5

When can static electricity be a nuisance?

Answer 5

TV screens and computer monitors gather dust, clothes cling to you, getting electric shocks in supermarkets.

Question 6

When can static electricity be dangerous?

Answer 6

When near fuels, e.g. when refuelling a plane or at a petrol station.

Question 7

How do we use static to remove smoke from chimneys?

Answer 7

• Smoke passes through a metal grid at high voltage.
• This charges the smoke particles.
• They are attracted to oppositely charged plates above the grid.
• This stops the smoke particles going into the air.
• The particles fall back down the chimney and are collected as ash.

Question 8

Explain why a circuit with a break in it will not work?

Answer 8

The electrons can not move around the circuit so it is incomplete.

Question 9

When can static electricity be useful?

Answer 9

Heart defibrillators, photcopiers, smoke precipitators, spray painting vehicles.

Question 10

Explain why plugs are made of rigid plastic.

Answer 10

So they don’t conduct electricity.

Question 11

What does a fuse wire do when too much current flows through it?

Answer 11

The fuse melts or blows. (NOT blows up!!!)

Question 12

List three wires found in a UK plug.

Answer 12

Earth, Live, Neutral

Question 13

What colour is the live wire?

Answer 13

Brown

Question 14

What colour is the earth wire?

Answer 14

The Earth wire is yellow/green.

Question 15

What colour is the neutral wire?

Answer 15

The neutral wire is blue.

Question 16

What happens to the resistance if a longer wire is used?

Answer 16

Resistance increases if the wire is longer (the electrons have more atoms to get past, so there are more collisions which slow the electrons down).

Question 17

What is the unit of resistance?

Answer 17

Resistance is measured in Ohms.

Question 18

What does an earth wire do?

Answer 18

The earth wire allows electrons to flow back to earth safely if the live wire comes loose and touches the metal case. The high current flowing back to earth melts the fuse so the circuit switches off.

Question 19

Describe how to measure the wavelength of a longitudinal wave.

Answer 19

Measure from one area of compressions to another area.

Question 20

What type of substances build static electricity?

Answer 20

Insulators - because the elctricity can’t flow througth an insulator which is why it’s called static!

Question 21

What is a defibrillator?

Answer 21

It is a machine used to restart a person’s heart after it has stopped.

Question 22

Why are the paddles on a defibrilator insulated?

Answer 22

So the person holding them does not get an electric shock.

Question 23

Name a use for ultrasound.

Answer 23

Baby scans, looking at body organs such as the liver and breaking up kidney stones.

Question 24

What property of ultrasound waves allows them to penetrate inside the body?

Answer 24

They are high frequency and have a short wavelength.

Question 25

What are the positive charges called?

Answer 25

Protons

Question 26

Which charges can move and which can not?

Answer 26

Electrons can move, protons can not.

Question 27

Describe how an acetate rod becomes charged when you rub it with a cloth.

Answer 27

When an acetate rod is rubbed with a woollen cloth, electrons move from the acetate rod onto the cloth. The acetate rod becomes positively charged, as it has lost negatively charged electrons. the cloth will be negatively charged as it gains electrons.

Question 28

If the length of a wire is increased, what happens to the current?

Answer 28

The current is reduced because the resistance will have gone up as the wire is longer.

Question 29

What are the areas of high pressure in a longitudinal wave called?

Answer 29

Compressions

Question 30

What are the areas of low pressure called in a longitudinal wave?

Answer 30

Rarefactions

Question 31

Why is ultrasound used instead of x-rays in baby scans?

Answer 31

Ultrasound is used instead of xrays in baby scans becuase **x-rays can damage living cells** and so could damage the fetus. Also, x-rays go straight through soft tissues, so would only show the bones.

Question 32

What does double insulated mean?

Answer 32

Double insulated appliances have plastic cases without any wires connected to the case. This means the case cannot become live because plastic does not conduct electricity.

Question 33

What is ultrasound?

Answer 33

Sound waves with a frequency greater than 20000Hz which humans cant hear.

Question 34

Explain how ultrasound can be used to produce a picture of an unborn baby.

Answer 34

Ultrasound reflects from boundaries between different tissues. The computer uses the time taken for these reflections.

Question 35

Explain the advantages of using static electricity to spray paint cars.

Answer 35

The advantages are that the spray paint all has the same charge, so it repels making a fine spray. Also, the car is the opposite charge to the paint meaning the paint is attracted to it. This makes it easier to paint odd shaped objects and wastes less paint.