7.8 understand that ionising radiations can be detected using a photographic film or a Geiger-Muller detector

Geiger-Muller detectors beep when ionizing radiation is detected. The faster the beep, the more radiation. NOTE: there will always be slow, steady beeps due to background radiation.

Photographic film is white. It absorbs radiation and turns black. NOTE: photographic film is used for X-rays, the bone part is white as the radiation is absorbed by the bone therefore the film behind it s not exposed to the radiation. Everywhere is the film where there is no bone is black as there is nothing blocking the radiation from getting through.

5.3 describe experiments to determine density using direct measurements of mass and volume

1. First, measure the mass of an object (weigh it)
2. Then measure the volume. If the object is irregular (e.g. not a cuboid/easily measurable-shape*, then take a set amount of water (eg. 100ml) and fully submerge the object in the water. Measure the rise of the water (eg. From 100ml to 130ml). Or measure using a eureka can. If object is regular, however, you can measure lengths to find the volume.
3. Use the equation density = mass/volume to find the density

*okay so easily-measurable shape isn't correct English but you get what I mean

4.8 explain how insulation is used to reduce energy transfers from buildings and the human body

NOTE: You only need to learn a few examples, I have included quite a few so you can choose and decide which ones you find easiest to remember.

Buildings

Loft insulation - a thick layer of fibreglass wool laid out across the loft floor and ceiling reduces heat loss from the house by conduction and convection

Hot water tank jacket - Fibreglass wool reduces conduction and convection

Draught-proofing - Strips of foam and plastic around doors and windows stop draughts of cold air blowing in (therefore, they reduce the amount of heat lost due to convection)

Cavity wall insulation - foam squirted into the gap between the bricks stops convection currents and radiation in the gap, the insulating foam and air trapped also help reduce heat loss by conduction

Thick curtains - Reduce heat loss by conduction and radiation

Double glazing - Two layers of glass with a small gap of air in-between them, this reduces conduction and convection

Humans

Hairs - When it's cold, the hairs on your skin stand up to trap a 'thick' layer of air all over the body (which will insulate the entire surface area). This limits the amount of heat loss by convection.

Clothes - reduce heat transfer. Pockets of air trapped between clothes reduce heat transfer by conduction (and a little convection). Also, clothes reduce the amount of heat radiated from the body (this is because the material absorbs some of the heat as it is radiated out of our bodies).

4.6 describe how energy transfer may take place by conduction, convection and radiation

Convection is the transfer of heat by the upward movement of less dense (warmer) gas/fluid and the downward movement of denser, colder gas/liquid. NOTE: convection can not occur in solids or in vacuums

Conduction is the transfer of thermal energy through a solid (the solid doesn't actually move)

Radiation is the transfer of thermal energy in infrared waves. This is also the only method of heat/thermal energy transfer that can occur in a vacuum

3.16 construct ray diagrams to illustrate the formation of a virtual image in a plane mirror

When light rays bounce off an object onto a mirror, a virtual image is formed. A ray diagram shows how this image is produced (in a plane mirror)

Method

- firstly, draw a line from the top of the object to the reflective surface (in this example it is a lake, although it could be a mirror/shiney surface etc)
- reflect the incidence engle in the reflective surface and draw the reflective
 (into a human eye_
- now continue the ray from the eye through the reflective surface until it is in line with the real image.
- repeat with a line from the bottom of the real image.
- the lines will now show where the top and bottom of the virtual image are, just fill in by drawing in the image.

(sorry that was a little confusing)

3.14 understand what light waves are transverse waves which can be reflected, refracted and diffracted

Light waves are transfers which means the energy travels perpendicular to matter.

The reflection of light is what lets us see things. Light bounces off objects into our eyes. the light ray will hit a reflective surface (e.g a mirror) and will bounce back at the same angle on the other side of the normal line.

If a wave refracts all it is doing is bending/changing direction. this occurs when a wave enters a medium of different density. When they return to the/a medium of the original density, they will travel in the same direction as started.


Diffraction is just when the waves 'disperse', sort of. If the waves hit a barrier with a small opening, they will bunch up and spread out after the opening, on the other side.

3.7 use the above relationships in different contexts including sound waves and electromagnetic waves

okay so the 'above relationships' are wave speed = frequency x wavelength and frequency = 1 / time period

We just need to be able to substitute what we are given in questions into the equation. Here are some examples...

1- Find the speed of a wave of wavelength 12m and frequency 4Hz

To answer this, we use the equation wave speed = frequency x wavelength, so, 12 x 4 = 48. Therefore, the wave speed of this wave is 48 seconds. (NOTE: fyi, this is a really unrealistic wave speed, this is just an example of how to sub in the equation!)

2- A wave has a period of 0.35 seconds. Find the frequency of this wave.

For this question, we need to use the equation frequency = 1 / time period. We know the period is 0.35, so all we need to do is 1 / 0.35 = 2.857 which rounds to 2.86. so the frequency of this wave is 2.86Hz

1.18 describe experiments to investigate the forces acting on falling objects, such as sycamore seeds or parachutes

- Make/obtain 5 paper parachutes that each have a different surface area.
- Drop each of the 5 parachutes 3 times from a given height (e.g. 2m)
- Time how long it takes for the parachute to reach the floor
- Find a mean time for each parachute (add up each of the 3 times and divide the number by 3). You should now have 5 values.
- Plot the values in a graph with size of parachute along the X-axis (in cm²) and time along the Y-axis (in s)
- Draw a line of best fit

7.19 understand that a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei

During nuclear fission, a slow-moving neutron gets absorbed by the nucleus of a U-235 atom. When this occurs, the atom splits into 2 daughter nuclei, whilst also releasing a small number of nuclei. If these nuclei his other uranion-235 atoms, these atoms will split and release more nuclei. The process will repeat. this is known as a chain reaction.

7.18 understand that the fission of U-235 produces two daughter nuclei and a small number of neutrons

In nuclear fission, a slow moving neutron gets absorbed by the nucleus of an U-235 atom. This causes the atom to split. The nucleus will split into two smaller 'daughter' nuclei and will also 'spit out' a small number of neutrons.

NOTE: When uranium-235 splits into two daughter cells, these cells will be radioactive as they will have the 'wrong' number of neutrons in them. They will also be lighter elements than uranium.

7.17 understand that a nucleus of U-235 can be split (the process of fission) by collision with a neutron, and that this product releases energy in the form of kinetic energy of the fission products

Nuclear power stations get there energy from a process of splitting atoms by collision with a neutron(as this releases energy). This is how...

If a slow moving neutron will get absorbed by an atom of uranium-235 (it will absorb into the nucleus). When this happens, the U-235 nucleus will split and spits out a small number of neutrons as it does.

This process releases energy (kinetic) and is converted into heat energy in the reactor by collisions with other atoms.

7.15 describe the results of Geiger and Marsden's experiments with gold foil and alpha particles

In an attempt to disprove the plum pudding model, Geiger and Marsden set up an experiment in which  they positioned a sheet of gold foil in a circle of zinc sulphide screen. They then aimed alpha particles at a sheet of thin gold foil. They concluded that most of the alpha particles went straight through the foil, and gave a tiny flash (a scintillation) when they hit the zinc sulphide screen. However, some of the alpha particles were deflected at 90º to the direction they were traveling, and some came straight back. This concluded that inside an atom there must be positively charged nuclei which repel the alpha particles (this is why they 'bounce off' at different directions).

7.14 describe the dangers of ionising radiations, including:  radiation can cause mutations in living organisms  radiation can damage cells and tissue  the problems arising in the disposal of radioactive waste and describe how the associated risks can be reduced.

Radiation can damage cells and tissue and mutations
Beta and gamma radiation are basically unharmful to humans as they can penetrate right out of the body. However, if alpha radiation gets inside the body, it can not escape as it cannot pass through human skin, therefore it can cause much damage. It collides with molecules, ionising them which will damage (and sometimes destroy) the molecule.

If the source is at a lower radiation, less damage will be done. For example, it can cause mutations, which can then divide uncontrollable, leading to serious medical conditions such as  cancer.

If the source is at a high dose, the cells tend to be killed. This can lead to radiation sickness if a large part of your body is affected at the same time.

NOTE: The extent of the effects depends on how much exposure you have to the radiation and how much energy it has (e.g. how many half-lives has it lived, like does it still have lots of activity or has it already expelled lots and lots).

However, although radiation can cause cancer, it can also be used to treat cancer. If a patient is given a high dose of gamma rays (directed at the cells in the tumour), this can kill those specific cells without harming many others.


The problems arising in the disposal of radioactive waste and describe how the associated risks can be reduced
Low-level waste from places such as hospitals and nuclear power stations (e.g clothing sonf syringes) can be easily disposed of by burying them in landfill sites.

However, high-level waste is very dangerous as it has a very long half-life, so can stay radioactive for a super long time (like 10s of 1000's of years). This waste is often sealed in glass blocks which are sealed in metal canisters which are buried deep underground.

NOTE: This is hard to do as the site must be 'geologically stable' meaning no earthquakes etc as this could cause leakages... which means we die, basically.

7.13 describe the uses of radioactivity in medical and non-medical tracers, in radiotherapy, and in the radioactive dating of archaeological specimens and rocks

Medical tracers
This method is used for doctors to find out whether a persons organs are working as they should be. Alpha can not be used as it does not penetrate human skin and is strongly ionising, but beta and gamma can be used at it will penetrate human skin and body tissue.

The process...
- A source which  emits beta or gamma radiation is injected or swallowed.
- The source moves around the body and the radiation will penetrate the body tissues and can be detected externally by a radiographer with a detector
- A computer converts the reading to a screen display which shows where the radiation is coming from

NOTE: The radioactive source they use would have to have a short half-life so it does not damage the person.

Non-medical tracers
Industrial tracers can be used for looking for things like leaks in underground pipes (using a tracer you would not need to dig out the pipe to find the leak, it's just a little bit less hassle).

The process...

- Put a gamma source into the pipe and let it flow through the pipe. Detect where the radiation goes with a detector above ground (follow it)
- When you reach the point where there is a hole in the pipe, there will b a much larger reading of radiation on the detector as lots of radiation will have escaped.

NOTE: A gamma source must be used, as beta or alpha would be stopped by the earths rocks and there would be a very little (if any) reading. It should also have a short half-life as it could cause damage if it stays/collects somewhere (think Chernobyl and Fukushima, but on a smaller scale)

Radioactive dating
Radioactive dating enables archaeologists to accurately work out the age of rocks, fossils and archaeological specimens (for example, Egyptian mummys)

If you know the half-life and amount of radioactive isotope in a sample, you can work out how long it has been around.

By comparing the activity level of an archaeological sample to a sample of living tissue, you can work out the amount of Carbon-14 half-lives that have passed (for example). This can give you an idea of how long ago the sample was living/died.

NOTE: an alternative is to look at the  ratio of Carbon-14 to Carbon-12 as this is fixed in living materials, so by comparing the ratio in a living and non living sample you can estimate the age of the sample.

7.12 use the concept of half-life to carry out simple calculations on activity

Okay so, this may be a bit confusing but here goes, this is best to show with an example...

E.g. the activity of a radioisotope is 640 Bq. Two hours later it has fallen to 40 Bq. Find the half-life of the sample.

All you have to do is keep dividing 640 until you reach 40... sort of.

Initial Bq is 640

After one half-life 640 / 2 = 320

After two half-lives 320 / 2 = 160

After three half-lives 160 / 2 = 80

After four half-lives 80 / 2 = 40

Okay so we made it to 40 in 4 half-lives, this means it took 4 half-lives for the activity to drop from 640 to 40, which took two hours, meaning 2 hours represents 4 half-lives, meaning each half-life is 30 minutes. So the half-life of this sample is 30 minutes

Answer = 30 minutes.

Example source: CGP

7.11 understand the term 'half-life' and understand that it is different for different radioactive isotopes

Definition for exams: half-life is the time taken for half of the radioactive atoms now present to decay.

It is very useful as there is a problem measuring how quickly the activity drops off for some isotopes, as they can last millions of years, so the half-life is used to measure how quickly activity falls off.

It is different for different isotopes as each isotope has a different amount of activity to expel. A short half-life means the activity fall quickly, because lots of the nuclei is decaying quickly (the half-life is short as it does not take up much time). A long half-life means the activity falls more slowly because most of the nuclei don't decay for a long time (the half-life is long as it takes a very very long time).

7.10 understand that the activity of a radioactive source decreases over a period of time and is measures in becquerels

A simple way to think of this is that each time decay happens, a little bit more of the radioactive nucleus has disappeared. As the unstable nuclei disappear, the activity as a whole will decrease (as less radiation will be given out).

The amount of radiation given out is measures in becquerels.

7.9 explain the sources of background radiation

Background radiation is just radiation that is everywhere but it is only at a low level so it doesn't harm humans :) It comes from...

- cosmic rays (from the sun)
-living things (there is a little bit of radioactive material in all living things - including you and me!)
- substances on Earth (e.g. air, food, soil, rocks, building materials)

NOTE: radiation can also occur due to human activity. For example, there is a very high amount of radiation surrounding the areas of Chernobyl and Fukushima since they are the scenes of nuclear power plant disasters

7.7 understand how to complete balanced nuclear equations

To do this all you need to know is the atomic and mass numbers of the original isotope, and the atomic/mass numbers of the particle/ray being emitted (these can both easily be worked out). You then put them in an equation... it is best to demonstrate with a few pictures...

Alpha radiation...

(the He part is the alpha particle)

Beta radiation...

(the e part is the beta particle)

Gamma radiation...

(the funny almost-Y shaped thing is the symbol for a gamma particle)

7.6 describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the three main types of radiation

An alpha particle is made up of 2 protons and 2 neutrons, therefore, when an alpha particle is emitted, the proton number will decrease by 2 (as 2 protons have been released) and the mass number will decrease by 4 (as 4 nucleons will have been released).

A beta particle is comprised of one electron, this means that when a beta particle is emitted, the atomic number will increase by one.

There is no effect on an atoms atomic or mass numbers if a gamma ray is emitted. This is because it is comprised of energy, not protons/neutrons/electrons.