4.17 describe the advantages and disadvantages of methods of largescale electricity production from various renewable and nonrenewable resources.

NOTE: advantages are in green, disadvantages are in red

Renewable
- hydro-electric power: very expensive, produces small amounts of electricity
- Solar panels: produce lots of energy, rely on weather
- Nuclear reactors/nuclear power: produces lots of energy quickly/easily, produces lots of harmful waste products
- Wind power: visual pollution; produces small amounts of electricity for space and effort in comparison to other methods, makes use of what we have (e.g. a 'free' energy source)

Non-renewable

Fossil fuels: finite source (will run out one day), releases CO2.

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.

7.5 describe the nature of alpha and beta particles and gamma rays and recall that they may be distinguished in terms of penetrating power

NOTE: so I just wrote down about everything I could find/knew on alpha and beta particles and gamma rays, there is no need to learn all of it but I put it all down so you can choose which parts to learn, it may be an idea to learn 3-4 facts about each or at least the main distinguishing features.

Alpha particles are made up os 2 protons and 2 neutrons - this means they are 'big' and heavy, and move quite slowly too. Because of this, they don't penetrate far into materials, however, they are strongly ionising (due to there size). This means that they collide with a lot of atoms and knock off their electrons, this creates lots of ions (hence the term 'ionising'). Due to the fact they are made of 2protons and 2 neutrons, they have a positive electric charge, because of this, they are deflected by electric and magnetic fields. Because of their composition (of 2 neutrons ad 2 protons), if an atom emits an alpha particle, its atomic number will decrease by 2 (as 2 protons will have 'gone') and its mass number will decrease by 4 (as. altogether, 4 nucleons have 'gone').

Beta particles are comprised of an electron. A beta particle is just an electron which has been emitted from the nucleus of an atom when a neutron turns into a proton and an electron...bit confusing (it basically just helps to balance the charge). They are quite small and move fairly fast, therefore they penetrate materials quite far (but not super far) and are quite ionising too (but not as much as alpha particles). When a nucleus emits an electron the number of protons in the nucleus will increase by 1, meaning the atomic number increases by 1 but the mass number stays the same (i don't really understand this it... help). Because beta particles are negatively charged (as they are comprised on one electron), they are deflected by electric and magnetic fields (like alpha particles).

Gamma rays have no mass, they are just made of energy and therefore can penetrate far into materials without colliding into anything - this means they very weakly ionise, as they often pass through instead of hit atoms (although they eventually hit one, therefore they are not not-ionising). Since they have no mass, they have no charge, therefore they are not deflected by electric or magnetic fields. the emission of gamma rays has no effect on the proton or mass number of an isotope, as it has no mass. If a nucleus has too much energy, this is when a gamma ray is emitted (as it is just made up of energy, so emitting it will 'get rid' of all the excess energy).

NOTE: Gamma rays are only emitted after either alpha or beta particles (or maybe both), they are never emitted by themselves.

Since each type of radiation penetrates a material to different extents, it is easy to identify what it is by its penetrating power.
- If it is stopped by thin materials, such as paper or skin, it is alpha.
- If it is stopped by mediumish thickness materials, such as a sheet of aluminium, but can pass through paper, it is beta
- If it can pass through paper and aluminium but not thick lead, it is gamma.

Here is a diagram that may help for understanding purposes...


image source: gtcceis.gov

7.4 understand that alpha and beta particles and gamma rays are ionising radiations emitted from unstable nuclei in a random process

Alpha and beta particles and gamma rays are emitted from unstable nuclei (in an attempt to make them more stable), this is known as radioactive decay. Radioactive decay is spontaneous and random, there is no (current) way of detecting when an unstable nucleus will decay and there is no way of speeding up/slowing down the process as it is completely unaffected by physical conditions (such as temperature of pH) or by and sort of chemical reactions/bondings.

NOTE: When a nucleus decays, it emits either alpha particles, beta particles or gamma rays (sometimes more than one kind, e.g alpha and gamma, or beta and alpha).

7.3 understand the terms atomic (proton)number, mass (nucleon) number and isotope

The atomic (or proton) number is just the amount of protons that are in an atom.

The mass number is the number of protons and neutrons in a nucleus

Isotopes are atoms with the same number of protons (so the same atomic/proton number) but a different number of neutrons (so  different mass number). However, because it is the number of protons in an atom that determine its element, the element is the same. That was confusing, here is an example that may help...

For example, carbon-13 and carbon-14 are both isotopes of carbon, as they all contain the same amount of protons but each have a different amount of neutrons.

Image source: experiment.com

7.2 describe the structure of an atom in terms of protons, neutrons and electrons and use symbols such as 14 C to describe a particular nuclei

The structure of an atom is super simple when you break it down... 

- all atoms contain a nucleus and electrons

- the nucleus of an atom is made up of protons and neutrons

- the total number of protons and neutrons is called the mass (or nucleon) number

- electrons surround the nucleus in electron shells

- the number of protons is the same as the number of electrons

- the number of protons/electrons is known as the atomic (or proton) number

From the mass number and proton number we can learn how many protons/neutrons an atom contains. For example, if an atom of carbon has a mass number of 14 and a proton number of 6, we know that there must be 6 protons in the nucleus. To find out how many neutron are in the shell, just minus the proton number from the mass number... 14 - 6 = 8, therefore there are 8 neutrons in this isotope of carbon.

7.1 use the following units: becquerel (Bq), centimetre (cm), hour (h), minute (min), second (s)

Becquerel, (Bq), measure of radioactivity
centimetre, (cm), measure of distance
hour, (h), measure of time
minute, (min), measure of time
second, (s), measure of time

sorry for delays!

As I have been back at school I have not been able to keep up with the blog as much as I was over Easter break.. I leave school this Friday for study leave and will be finishing all blogs next week (iGCSE Chemistry, iGCSE Physics and iGCSE Biology), sorry for any inconvenience, thank you for sticking with me! If you have any questions about any posts do not hesitate to comment and I will reply as soon as possibly, hope any exams you have already done went smoothly (for those doing Cambridge iGCSE english... what was the obsession with the bees?), good luck for any doing art and textiles exams over the next few days also. I will endeavour to finish the blogs as soon as possible next week so I have all the rest of study leave to answer any questions or anything you have. Good luck once more, I know you will all do amazing :)

Millie

5.17 use the relationship between pressure and volume of a fixed mass of gas at constant temperature

P1 x V1 = P2 x V2

NOTE: this is sometimes written as P1 x V1 = constant

For example: A gas at a pressure of 250 kilopascals is compressed from a volume of 300cm3 down to a volume of 175cm3. The temperature of the gas does not change. Find the new pressure of the gas, in kilopascals.

Step 1: rearrange the equation to isolate one unknown

In this instance, we know P1, V1 and V2, and we are looking for P2. Therefore...

P2 = (P1 x V1) / V2

Step 2: substitute the known to find the unknown...

P2 = (250 x 300) / 175

P2 = 429 kPa (to 3 significant figures)

Example credit: CGP

5.16 use the relationship between pressure and kelvin temperature of a fixed mass of gas at constant volume

P1 / T1 = P2 / T1

Example: A container has a volume of 30 litres. It is filled with a gas at a pressure of 100 kPa and a temperature of 290 K. Find the new pressure (in kPa) if the temperature is increased to 315 K.

Step 1: rearrange the equation to isolate the unknown

The old pressure is P1
The old temperature is T1
The new pressure is P2 (this is what we are finding)
The new temperature is T2

if P1/T1=P2/T2 and we are looking for P2, we must rearrange the equation to...

P2 = (P1/T1) x T2

Step 2: substitute the known into the equation

P2 = (100 / 290) x 315

 = 109 kPa

NOTE: as we are asked to leave the new pressure in kPa, we do not need to convert it, if asked to leave the answer in Pa (and you have it in kPa) just multiply it by 100

Example credit: CGP

5.15 describe the qualitative relationship between pressure and Kelvin temperature for a gas in a sealed container

In a sealed container, temperature (in K) and pressure are proportional. This is because the higher the temperature the faster the molecules move the more pressure is exerted onto the walls of the sealed container. If you double the temperature, you double the kinetic energy (5.14), this will double the pressure.

5.14 understand that the Kelvin temperature of the gas is proportional to the average kinetic energy of its molecules

Temperature (in Kelvin) and kinetic energy are proportional. In other words, if you double the temperature, you will double the average kinetic energy of the particles. This is because as you increase temperature, the particles gain more kinetic energy.

5.13 understand that an increase in temperature of the gas is proportional to the average kinetic energy of its molecules

An increase in temperature means the particles will have more energy. In a gas, this means the particles will travel further (in a solid, the particles will break the intermolecular forces and become a liquid, in a liquid they will gain speed to become a gas).

5.12 describe the Kelvin scale of temperature and be able to convert between Kelvin and Celsius scales

Absolute 0, -273ºC, is the start of the Kelvin temperature scale (basically, 0K is -273ºC). The two temperature scales (ºC and K) have the same temperature change (e.g. a change of 12ºC is also a change of 12K) which is handy as it means conversion is super simple.

In order to convert from K to ºC all you need to do is -273 (and change the unit from K to ºC). Alternatively, to convert from ºC to K just ass 273. For example..


0K = -273ºC
0ºC = 273K
100ºC = 373K

NOTE: there is a little more information on Kelvin and absolute 0 (-273ºC) in post 5.11

5.11 understand why there is an absolute zero of temperature which is -273ºC

The coldest something can get is -273ºC (0K), this is because atoms have as little energy as they can possible have at this temperature (more heat = more energy, less heat = less energy). This temperature is known as absolute 0.

NOTE: to convert from ºC to K, just add 273. Alternatively, to convert from K to ºC just take away 273

NOTE NOTE: there is no º symbol when talking about degrees Kelvin, it is just a K

5.10 understand that molecules in a gas have a random motion and that they exert a force and hence a pressure on the walls of a container

Particle theory suggests that gas molecules has a random motion. When gas molecules collide with something (could be anything as they move in a random motion) they exert a force. If the gas is present in a sealed container they will exert an outward force should they hit the walls of the container.

NOTE: The pressure exerted is not the same for every gas/molecule, it will depend on how fast the particles are going and how often (as they will have more/less kinetic energy. The overall pressure felt on the object will depend on how fast the molecules are going and how often gas particles collide with its walls (more collisions = more force).

5.9 understand the significance of Brownian motion, as supporting evidence for particle theory

Brownian motion states that particles move in a random unpredicted motion (like they dont all more from north to south, or from up to down, they move wherever). Particle theory states that gases consist of particles that are constantly moving in a random direction.

These two theories support each other as particle theory claims that particles are constantly moving in a random motion, and Brownian motion claims that particles move in a random motion.

NOTE: Both of these theories can help explain post 5.5

5.8 describe the arrangement and motion of particles in solids, liquids and gases

NOTE: again, if you are unsure of these/need a little more guidance it may be an idea to check out my chemistry blog (this time post 1.1) as there is a little more information there just describing the formation of particles/changes in the conversion triangle etc.

image credit: oxnotes

5.7 understand the changes that occur when a solid melts to form a liquid, and when a liquid evaporates or build to form a gas

Solid to liquid - when a solid is heated, its particles gain more energy, this makes the particles vibrate more which weakens the forces that hold a solid together, this makes the solid expand. At a certain temperature, known as 'boiling point' (different for different substances), the particles have enough energy to break free from their positions.

Liquid to gas - when a liquid is heated it will evaporate/boil. When this happens, the particles gain more energy, this energy makes the particles move faster which weakens and breaks the bonds holding the liquid together. At a certain temperature (different for different substances), the particles have enough energy to break their bonds.

NOTE: if you are unsure of these or need a little more info to understand, it may be able to head to post 1.2 of my chemistry blog where there is a little more info on interconversions

5.6 know and use the relationship for pressure difference

pressure difference = height x density x gravitational constant


p = h x ρ x g

NOTE: You may have learnt the gravitational constant on earth to be approximately 9.8 (as did I) BUT it is rounded to 10 for iGCSE exams (it's on the formula sheet) so make sure to use 10 in exams not 9.8

For example...

The density of water is 1g/cm³. Find the pressure difference between the top and bottom of a 3m vertical column of water.

First, convert all units into the same (sorry, that didn't make much sense). Basically what im saying os ensure all measurements are in the same unit, like all distance is in m (or cm) and all mass is in kg (or g) etc. In this particular example, we need to convert 1g/cm³ into kg/m³ (alternatively, you could convert the 3m into cm, but for now lets stick with kg/m³). So...

1g/cm³ = 1000kg/cm³ and in this example we only have 1g/cm³ so no calculations regarding units have to take place :)

Next substitute all the facts we are given into the equation 'pressure difference = height x ρ x g

Pressure difference = 3 x 1000 x 10 = 30,000 Pa

NOTE: Pa (pascals) is equivalent to N/m² so don't be thrown of in an exam situation if the unit given is N/m² (it basically means pascals, the unit for pressure)

example credit: CGP

5.4 know and use the relationship between pressure, force and area:

pressure = force / area

p = F / A

NOTE: do not get confused with p (pressure) and  ρ (rowe, density)

5.5 understand that the pressure at a point in a gas or liquid which is at rest acts equally in all directions

Pressure is a measure of the force being applied to the surface of something. In gases and liquids (at rest) the pressure at any point acts equally in all directions. for example, if you fill a bag with water, then poke a hole at the bottom of the bag, water will 'squirt' out of the bag (obviously). However, if you put a hole near the top of the bag, the water will 'squirt' out with the same force. This is because the pressure of the water is the same at the top of the bag as it is in the  bottom of the bag.

5.2 know and use the relationship between density, mass and volume:

density = mass / volume

ρ = m / v


NOTE: do not get confused with p (pressure) and  ρ (rowe, density)

5.1 use the following units: degrees Celsius (oC), kelvin (K), joule (J), kilogram (kg), kilogram/metre3 (kg/m3), metre (m), metre2 (m2 ), metre3 (m3), metre/second (m/s), metre/second2 (m/s2 ), newton (N), pascal (Pa)

degrees Celsius, oC, measure of temperature
kelvin, K, measure of temperature
joule, J, measure of energy
kilogram, kg, measure of mass
kilogram/metre3, kg/m3, measure of density (interchangeable with g/cm3)
metre, m, measure of distance
metre2, m2 , measure of area
metre3, m3, measure of volume
metre/second, m/s,  measure of speed
metre/second2, m/s2,  measure of acceleration
newton, N, measure of force
pascal, Pa, unit of pressure

4.15 use the relationship between power, work done (energy transferred) and time taken:

Power = work done / time taken

P = W / t

For example...

A motor transfers 4.8kJ of useful energy in 2 minutes. Find it's power output...

As work done is the same as energy transferred, we know that 4.8kJ of work was done. Therefore...

4800 / (2 x 60) = 4.8 / 120 = 40 W

NOTE: remember to convert kJ to J and minutes into seconds.

4.14 describe power as the rate of transfer of energy or the rate of doing work

Power is the rate of energy transfer, or the rate of doing work, it is different to force and energy. The unit for power is watts (W), 1 watt = 1 joule of energy transferred per second. This means a watt is the same as a 'joule per second', they are interchangeable, watt is more commonly used just because few people may get confused with 'joule' and 'joule per second' (which are vert different things).

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

When something is falling, GPE is being converted into KE. This means that the further it goes, the faster it falls (well, until it reaches terminal velocity), as it is gaining more KE the further it has fallen. This equation may be useful to remember...

Kinetic energy gained = gravitational potential energy lost

4.12 know and use the relationship: kinetic energy = 1/2 x mass x speed2

0. 0. kinetic energy = 0.5 × mass × speed2 
      
   
   
   KE = 0.5 x m x v 2 
   

4.11 know and use the relationship: gravitational potential energy = mass x g x height

Gravitational energy = mass x g x height

GPE = m x g x h

NOTE: g stands for gravitational constant, which is around 9.8 on earth (rounded to 10 for exam purposes)

4.10 understand that work done is equal to energy transferred

Pretty self explanatory... work done is another way of saying energy transferred.

Basically, when a force is moves on an object, energy is transferred and work is done.

4.9 know and use the relationship between work, force and distance moved in the direction of the force:

Work done = force x distance moved


W = F x d


Example...

A tow truck drags a car 5m with a force of 340N, find the work done.

5 x 340 = 1700J

NOTE: Work done is measured in Joules, this is because it is the same as energy transferred (and energy is measured in Joules)

4.7 explain the role of convection in everyday phenomena

In everyday phenomena, convection can be useful as it will move hot air upwards. This can be useful when heating a room - hot, less dense, air by the radiator rises, its place is filled with cool, dense air, this heats, rises etc.

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate pf the input energy in terms of the above relationship, including their representation by Sankey diagrams

Of course all things aim to be 100% efficient, but  thats virtually impossible. A Sankey diagram is a good way to visualise how much energy is wasted/useful (the more useful energy that goes out, the more efficient the object is). For example...

The useful energy output for a lightbulb is light energy, because thats what we want to come out. However, some of the electrical energy is transferred into heat energy. This is an example of a very inefficient lightbulb, only 10% of the energy input comes out as useful energy, the rest comes out as heat (wasted) energy.

NOTE: Inefficiency is the same for many everyday situation, e.g. a fire (for warmth) creates light; a pepper grinder creates sound (even though you just want it to move).

NOTE NOTE: In Sankey diagrams, the 'down' arrow (s) is the wasted energy, the 'straight' arrow(s) is the useful energy

4.4 know and use the relationship: efficiency = useful energy output / total energy input

Pretty self explanatory... efficiency = useful energy output / total energy input

4.3 understand that energy is conserved

Energy can never be 'lost' or 'used up', only every transferred. For example, when you turn a light on, electrical energy transfers to light energy (and a little heat energy).

4.2 describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

This basically means what are the types of energy...

Electrical energy > whenever a current is flowing
Light energy > from the sun, light bulbs etc (when light is 'given off')
Sound energy > noise, e.g. when you should, or from a loudspeaker
Chemical energy > in foods , fuels, batteries etc
Kinetic energy > movement (everything moving has kinetic energy)
Nuclear energy > released nuclear reactions (and nothing else)
Thermal energy > this flows from hot objects to cold ones (also known as heat energy)
Gravitational Potential Energy (GPE) > anything that has the potential to fall has GPE. E.g. if you hold a tennis ball, it has GPE.
Elastic Potential Energy (EPE) > anything that can stretch has EPE. For example an electric band or a spring

NOTE: GPE, EPE and chemical energy are forms of stored energy, because the energy is not doing anything (unlike kinetic energy, for example), its just sort of there.

4.1 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s), watt (W).

kilogram, (kg), measure of mass
Joule,(J), measure of energy
Metre, (m), measure of distance
Metre/second, (m/s), measure of speed
Metre/second2, (m/s2), measure of acceleration
Newton, (N), measure of force
Second, (s), measure of time
Watt, (W), measure of power

3.32 relate the loudness of a sound to the amplitude of vibration

If there is a bigger amplitude, the sound will be louder, if there is a smaller amplitude, the sound will be quieter.

3.31 relate the pitch of a sound to the frequency of vibration of the source

The frequency is the complete number of vibrations per second. If the wave has a high frequency, the pitch is high (e.g a squeak), comparatively, if you have a low frequency (not very many oscillations per second), the pitch will be low (e.g a bear).

3.30 describe an experiment using an oscilloscope to determine the frequency of a sound wave

Method

- Plug a microphone into an oscilloscope
- Make a noise into the microphone (e.g. have someone sing a single note)
- Count the amount of oscillations per second (an oscillation is one complete wave, basically the wavelength)\

This is the frequency (as frequency is wavelength/time)

3.29 understand how an oscilloscope and microphone can be used to display a sound wave

A sound wave receiver (microphone, for example) picks up sound waves that are trade;;ing through the air. In order to display these waves (which is useful for measuring properties etc), you can plug the receiver into an oscilloscope (a decide which displays he microphone signal as a trace on a screen). The receiver will convert the sound waves to electrical signals. The appearance of the wave (basically what it looks like) can tell you whether the sound is loud or quiet, low or high pitched etc. You can also take measurements to calculate frequency etc (this is done by adjusting the display of the oscilloscope).

Reading the oscilloscope - the greater the amplitude of the wave, the more energy it carried. In sound, this means the greater the amplitude the louder the sound.

3.28 describe an experiment to measure the speed of sound in air

If you attach a signal generator to a speaker you can generate sounds with a specific frequency. By using two microphones and an oscilloscope you can find the wavelength of the sound waves generated. NOTE: the detected waves at each microphone can be seen as a separate wave on the oscilloscope.

Method

- Start with both microphones next to the speaker
- Slowly move one away until the two waves are aligned but exactly one wavelength apart (displayed on the oscilloscope)
- Measure the distance between the microphones to find the wavelength (λ)
- use the formula v = f x λ to find the speed (v) of the sound waves passing through the air. NOTE: the frequency is whatever you set the signal generator to.

Conclusion
Should all go well... you should find that the speed of sound in air is roughly 340 m/s

3.27 understand that the frequency range for human hearing is 20Hz - 20,000 Hz

Not much to explain here... the frequency range for human hearing is 20 Hz - 20,000 Hz.

3.26 understand that sound waves are longitudinal waves and hoy they can be rejected, refracted and diffracted

Sound waves are longitudinal waves. They can be reflected by hard flat surfaces. Materials such as carpets and curtains act as absorbing surfaces (they absorb sounds rather than reflect them). Sound waves refract as they enter a different medium (the denser the a material, the more they speed up). Sound waves can also be diffracted through gaps and around obstacles (such as a wall).

3.25 describe how digital signals can carry more information

If analogue waves are similar frequency, they can interfere with each other and lose signal quality. However, with digital signal it is much easier to tell the two waves apart, meaning more information can be transmitted along the same channel.

Furthermore, there is a process called quantisation. This is the rounding of multiple values to a smaller set. By doing this, more information can be packed into the same amount of space. As digital signals only have two values, not much information (if any) is lost due to quantisation. However, a lot can be lost when analogue is quantised.

3.24 describe the advantages of using digital signals rather than analogue signals

Firstly, it is important to understand that both digital and analogue signals get weaker as they travel, so they need to be amplified along their route. Also, both signals pick up noise/interference from electrical disturbances or other signals. 

However, when you amplify analogue signal, the nose it has picked up is amplified too, this worsens the quality of the signal. With digital signal, the noise is not amplified meaning the signal quality remains high.

3.23 understand the differences between analogue and digital signals

An analogue signal can take any value within a certiain range. The amplitude and frequency of an analogue wave can vary constantly.

A digital signal can only take two values. These values tend to be called either ON/OFF or 1/0. For example, you can send data along optical fibres as short pulses of light.

NOTE: a good way to remember which is which is that analogue is any

Credit source: CGP

3.22 know and use the relationship between critical angle and refractive index

sin c = 1 / n

NOTE: n means refractive index

3.21 explain the meaning of critical angle c

When light travels through different materials, it is refracted. If light ray is shone through a medium at certain angle (known as the 'critical angle' or 'angle c') the light will be refracted at 90º. If the light ray is shone at a greater angle than angle c, the light will be reflected back into the medium it is in (this is known as total internal reflection).

This diagram shows what happens when a ray of light is shone at angle c...

NOTE: the critical angle is different for different mediums

3.20 describe the role of total internal reflection in transmitting information along optical fibres and in prisms

Optical fibres (which are made of glass or plastic), consist of a central core surrounded by cladding that has a lower refractive index (of the glass or plastic). The central core is so narrow that light signals passing through the core always hit the cladding boundaries at angles higher than C (critical angle). This means that the light is always totally internally reflected. This total internal reflection will only not occur if the optical fibre is bent too sharply.

Optical fibres are used to transmit information. Total internal reflection is very useful in optical fibres as no information is lost (it is all reflected back into the core), also, light travels very fast.

3.19 describe an experiment to determine the refractive index of glass, using a glass block

Method
- Draw around a rectangular glass block.
- At an angle, shine a ray of light (from a light box) through it. Trace the incident and emergent rays.
- Take away the glass block, draw the refracted ray (by joining up the incident and emergent rays).
- At the point where the ray entered the block, draw the normal at 90º to the edge of where the block was.
- Use a protractor to measure the angle if incidence (i) and the angle of refraction (r). NOTE: remember to measure from the normal line
- Calculate the refractive index (n) using the equation n = sin i / sin r

Presuming all is well, your diagram should look something like this...

3.18 know and use the relationship between refractive index, angle if incidence and angle of refraction

the refractive index of a transparent material tells you how fast light travels in that material. The slower the light travels, the higher the refractive index

n = sin i / sin r


NOTE: n symbolises refractive index, i symbolises angle of incidence, r symbolises angle of refraction

3.15 use the law of reflection (the angle if incidence equals the angle of reflection)

The law of reflection applies to every single reflected ray...

Angle of incidence = angle of reflection

NOTE: these two angles are always measured between the normal (dotted line) and the ray itself.

3.13 understand the detrimental effects of excessive exposure of the human body to electromagnetic waves and describe simple protective measures against them

Microwaves: internal heating of body tissue
Problem: Microwaves have a similar frequency to the vibrations of many molecules and so they can increase these vibrations, resulting in internal heating. In this way, microwaves can internally heat human body tissue.

Protective measure: microwaves ovens need to have shielding to prevent microwaves escaping and reaching the person using it (or anyone else around)


Infrared: skin burns
Problem: he infrared range of frequencies can make the surface molecules of substances vibrate, like microwaves, this results in a heating effect. However, infrared has a higher frequency, so it carries more energy than microwave radiation. IF human flesh is exposed to too much IR radiation, skin burns can result.

Protective measure: you can protect yourself using insulating materials to reduce the amount of IR reaching your skin.


Ultraviolet: damage to surface cells and blindness
Problem: UV radiation can damage surface cells and cause blindness. It is 'ionising', this means it carries enough energy to knock electrons off atoms. This can case cell mutations (which can lead to cancer)

Protective measure: Wear suncream with UV filters if out in the sun and stay out of strong sunlight


Gamma rays: cancer, mutation
Problem: Gamma rays have very high frequency and are ionising, they carry more energy than UV rays and therefore can penetrate the body much further. They can cause cell mutation or destruction, which leads to tissue damage and cancer.

Protective measure: Radioactive sources of gamma rays should be kept in lad-lined boxes when not in use. Should someone need to be exposed to gamma radiation(e.g. in chemotherapy) the exposure time should be kept as short as possible.

Source of most information: CGP

3.12 explain some of the uses of electromagnetic radiations

Radio waves: broadcasting and communications
Radio waves are used mainly for communication. This is because they have long wavelengths (over 10m) which s very useful. Long-wave radio (wavelengths of 1-10km) can be transmitted from London (for example) to half way around the globe. This is because long wavelengths are the best at diffracting, so they can bend around the earth and also arounds opticals such as hills and tunnels.

Radio waves used for broadcasting have mush shorter wavelengths (10cm-10m), these do not bend well so you have to be in direct sight of the transmitter, the is why T.V ariels are positioned on top of houses.

NOTE: as well as long-wave radio signals, short-wave and medium-wave also exist. Short wave radio signals (10m-100m) can also be received  long distance from the transmitter because they are reflected from the ionosphere (an electrically charged layer in the Earth's upper atmosphere). Medium-wave signals can also reflect from the ionosphere (but this depends on the atmospheric conditions and the time of day)


Microwaves; cooking and satellite transmissions
Microwaves have wavelengths of around 1cm-10cm, they are used for satellite communication and cooking. 

Satellite communication needs to use wavelengths of microwaves which can easily pass through the Earths atmosphere without bing absorbed. For a satellite T.V (for example) to work, the signal from a transmitter is transmitted into space where it is picked up by the satellite receiver did that is orbiting thousands of kilometre above Earth. The satellite transmits the signal back to Earth in a different direction where it is received by a satellite dish on the ground. Mobile phone calls also travel as microwaves from your phone to the nearest transmitter.

Microwaves in ovens have a different wavelength to those used in communication. These microwaves penetrate  a few centimetres into the food before being absorbed by water molecules in the food.


Infrared: heaters and night vision equipment
Infrared radiation is also known as heat radiation. Infrared radiation is given out anything and everything, and the hotter the object, the more IR radiation is given out. Examples of infrared radiation in everyday phenomena include electrical heaters and grills. Electrical heaters radiate infrared to keep us warm and grills radio infrared to cook food.


Furthermore, the infrared radiation that objects give out can be picked up/detected during nighttime (or pitch black) by night-vision equipment. the equipment turns the IR that has been radiated into an electrical signal which is displayed on a screen as a picture, meaning things that otherwise would go amiss (e.g. a criminal hiding) to be seen.


Visible light: optical fibres and photography
Visible light can also be used in communication using optical fibres which carry data over long distances as pulses of light.

Optical fibres work by bouncing waves off the sides of a very narrow core. The beam of light enters the fibre at a certain angle as one end and is reflected again and again (known as 'total internal reflection' until it emerges at the other end...


Optical fibres are often used for telephone and broadband internet cables. They are also used in hospitals to see inside the body without having to operate.

Visible light is also used for photography. Cameras use a lens to focus visible light onto a light-sensitive film or electronic sensor (the lens aperture controls how much light enters the camera). The shutter speed determine how long the film or sensor is exposed to the light. by varying the aperture and shutter speed a photographer can capture as much/little light as they want

Ultraviolet: fluorescent lamps
Florescent colours look so bright because it is where ultraviolet radiation (UV) is absorbed and visible light is emitted.

This basically means that fluorescent lights use UV radiation to emit visible light. They are safe to use as nearly all the UV radiation is absorbed by a phosphor coating on the inside of the glass (which emits visible light instead). This is more energy-efficient than filament light bulbs.


X-rays: observing the internal structure of objects and materials and medical applications
To produce an X-ray image, X-ray radiation is directed through your body (or an object you wish to X-ray) onto a detector plate (which starts off white). X-rays can easily pass through mediums such as flesh but not through dense mediums such as bone. The brighter bits (e.g. bones) are where fewer X-rays get through - this is a negative image.


Gamma rays: sterilising food and medical equipment
Medical equipment is sterilised by gamma rays as they kill ass the microbes. This is more effective than boiling equipment as this could potentially cause damage.

Food can be sterilised the same was as medical equipment (by killing the microbes). Is is perfectly safe to eat afterwards, as in like its not radioactive etc.