PHYSICS P4

Question 1

How could the plum pudding model be described and who came up with it?

Answer 1

• A ball of positive charge with negative electrons embedded in the ball
• JJ Thomson, 1897

Question 2

Which scientist discovered the neutron?

Answer 2

James Chadwick, 1932

Question 3

What did Rutherford find when he tested the plum pudding model?

Answer 3

• Most of the alpha particles did not pass straight through the foil
• A small number of alpha particles were deflected by large angles as they passed through the foil
• A very small number of alpha particles came back off the foil

Question 4

What did Rutherford conclude after he tested the plum pudding model?

Answer 4

• The atom is mostly empty space because most of the alpha particles went straight through the atom
• Proved that the plum pudding model was incorrect
• The small number of particles coming back suggested that the positive charge and the mass of the atom are connected at a tiny volume.

Question 5

What did Rutherford describe the atom to be like?

Answer 5

The nuclear atom, a small, positively-charged
nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom.

Question 6

What did Niels Bohr suggest about the atom?

Answer 6

That the electrons orbited the nucleus in different energy levels or at specific distances from the nucleus.

Question 7

What is the radius of an atom?

Answer 7

1x10, to the power of -10, metres.

Question 8

What is the relative mass of an electron?

Answer 8

1/2000

Question 9

What does the total number of protons tell us about the element?

Answer 9

This is called the atomic number

Question 10

What does the total number of protons and neutrons tell us about the element?

Answer 10

This is called the mass number

Question 11

What is said about the number of protons and electrons in a neutral atom?

Answer 11

The number of electrons is always the same as the number of protons.

Question 12

What happens when a neutral atom becomes ionised?

Answer 12

The number of electrons changes.

Question 13

What is an ion?

Answer 13

An atom that has lost or gained one or more electrons.

Question 14

What is an isotope?

Answer 14

An atom of an element with the same number of protons but a different number of neutrons.

Question 15

Why are atoms more unstable if the number of protons is increased?

Answer 15

More neutrons are then needed to keep the nucleus stable e.g. lead 206 is stable because it has 82 protons and 124 neutrons.

Question 16

What happens to nuclei when they have too many or too few neutrons?

Answer 16

They still exist but are unstable and will decay by emitting radiation.

Question 17

What are the four ways that an unstable nucleus can decay?

Answer 17

By emitting:
- An alpha particle
- A beta particle
- A gamma ray
- A single neutron

Question 18

What’s an alpha particle made up of?

Answer 18

Two protons and two neutrons

Question 19

What’s a gamma ray made up of?

Answer 19

An electromagnetic wave

Question 19

What’s a beta particle made up of?

Answer 19

A high speed electron ejected from the nucleus

Question 20

How does alpha, beta and gamma decay all affect the atom number and the mass number of an element?

Answer 20

Alpha - Mass decreases by 4, atomic decreases by 2
Beta - Mass stays the same, atomic increases by 1
Gamma - Mass and atomic stays the same

Question 21

Which type of decay is the most ionising and the least ionising?

Answer 21

Most - Alpha
Least - Gamma

Question 22

What’s the range of alpha, bet and gamma decay in the air?

Answer 22

Alpha - 5cm, stopped by skin or paper
Beta - 1 metre, stopped by 3mm of aluminum
Gamma - Around 1km, stopped by lead/concrete

Question 23

How can radioactive decay be detected and how does this machine work?

Answer 23

1. Using a geiger-muller tube
2. The radiations ionise the gas inside and the resulting charged particles move across the chamber and get counted as charges.

Question 24

What is meant by the term 'half-life'?

Answer 24

The time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.

Question 25

Practice some example half-life questions.

Answer 25

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Question 26

What is irradiation?

Answer 26

Process of exposing an object to a source of radiation.

Question 27

What can irradiation be used for?

Answer 27

- Can be used to preserve fruit that is sold in supermarkets to kill any bacteria on the fruit - Sterilization - Security

Question 28

What are some of the pros and cons of using irradiation?

Answer 28

Pros: - Sterilisation can be done without high temperatures - It can be used to kill bacteria on things that would melt Cons: - It may not kill all bacteria on an object - It can be very harmful - standing in the environment where objects are being treated by irradiation could expose people’s cells to damage and mutation

Question 29

How can we make sure that contamination doesn't cause any long-term effects to the body?

Answer 29

- Choosing isotopes that have short half-lives - Choosing isotopes that aren't poisonous

Question 30

When does contamination occur?

Answer 30

When an object has radioactive material introduced into it.

Question 31

What are some of the pros and cons of contamination?

Answer 31

Pros: - Radioactive isotopes can be used as medical and industrial tracers - Use of isotopes with a short half-life means exposure can be limited Cons: - Radioactive isotopes may not go where they are wanted - Exposure to radioactive materials can potentially damage healthy cells

Question 32

What are some of the safety precautions that can be put in place when dealing with radioactive sources?

Answer 32

- Keep radioactive sources shielded - Wear protective clothing - Avoid contact with bear skin - Wear face masks to avoid breathing in materials - Limit exposure time - Handle radioactive materials with tongs

Question 33

What are some examples of background radiation - ionising radiation that happens around us all the time?

Answer 33

- Food and drink - Buildings and the ground - Cosmic rays - Radon gas

Question 34

What is the unit for radioactivity?

Answer 34

Becquerels (Bq)

Question 35

What is 'activity'?

Answer 35

The number of decays per second from an unstable nucleus.

Question 36

What is nuclear fission?

Answer 36

The splitting of a large atomic nucleus into smaller nuclei.

Question 37

What happens in the process of nuclear fission in a reactor?

Answer 37

The entire nucleus splits into two large fragments called ' daughter nuclei' after having an extra neutron put into uranium causing it to become unstable. In addition to the 'daughter' products, two or three neutrons also explode out of the fission reaction and these can collide with other uranium nuclei to cause further fission reactions. This is known as a chain reaction.

Question 38

Go onto bitesize and learn the different parts of a fission reactor.

Answer 38

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Question 39

What do the control rods do in a fission reactor?

Answer 39

They are raised and lowered to stop neutrons from travelling between fuel rods and they can change the speed of the chain reaction.

Question 40

What does the graphite core do in a fission reactor?

Answer 40

It slows the neutrons down so that they are more likely to be absorbed in a nearby fuel rod.

Question 41

What is nuclear fusion?

Answer 41

When two small, light nuclei join together to make one heavy nucleus.

Question 42

When do fusion reactions occur?

Answer 42

In stars where two hydrogen nuclei fuse together under high temperatures and pressure to form a nucleus of a helium isotop. e.g. on the sun

Question 43

What is radiation dose measured in?

Answer 43

Sieverts (sv)