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.

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.

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

5.14 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.

5.8 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

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.

3.26 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

3.9 understand that waves can be diffracted through gaps, and that the extent of diffraction depends on the wavelength and the physical dimension of the gap

The size of the gap relative to the size of the wavelength is also important...

3.8 understand that waves can be diffracted when they pass an edge

When a wave meets an obstacle, it could be reflected, refracted or diffracted.

If they are diffracted this just means that the edges of the waves 'bend' to get through gaps, this causes the waves to spread out and allows for waves to travel around corners.

The amount of diffraction depends on the size of the gap relative and the wavelength of the wave, the narrower the gap or the longer the wavelength, the more the wave spreads out

Here's what happens...

2.25 explain some uses of electrostatic charges, e.g in photocopiers and inkjet printers

Photocopiers

In photocopiers, there is an image plate which is positively charged, an image of what you are photocopying is then projected onto it. The charge leaks away from the white/light parts of what your copying as they make light fall on the plate. The dark/black parts of what your copying remain charged and attract negatively charged black power, which is transferred onto positively charged paper. Next, the paper is heated to stick the powder down.

Inkjet printers

In an inkjet printer, tiny droplets of ink are forced out of a fine nozzle, this makes them electrically charged. The droplets are then deflected as they pass between two metal plates. A voltage is applied to the plates, one is negative and the other is positive. The droplets are attracted the the plate of the opposite charge and repelled from the plate with the same charge - the size and direction of the voltage across each plate constantly changes so that each droplet is deflected to hit a different place on the paper.

2.23 explain electrostatic phenomena in terms of the movement of electrons

This is quite confusing and may need a few reads to fully understand...

The movement of electrons is responsible for all phenomena relating to current electricity. However, electrostatic phenomenon, such as electrostatic induction , is the transfer of electrons from one body to another.

For example, polythene and cloth. When they are rubbed together, the rod will gain electrons and become positively charged and the cloth will lose electrons and become negatively charged.

2.24 explain the potential dangers of electrostatic charges, e.g when fuelling aircraft and tankers

Problem

As fuel flows out of a filler pipe (the pipe thing that you put in your car, etc), static electricity can build up. This can easily lead to a spark, which can cause a fire in dusty/fumy places.


Solution

Make the nozzle of the filler pipe out of metal so that the charge is conducted away instead of building up (as the building up of electrostatic charge will cause a spark).

It is also good to have earthing straps between a feeling tank and the fuel pipe, to earth the charge, avoiding a build up of the charge.

2.22 understand that there are forces of attraction between unlike charges and forces of repulsion between like charged

- Two materials with opposite electrostatic charges are attracted to each other
- Two materials with the same electrostatic charge will repel

NOTE: like magnets, these forces get weaker the further apart the two materials are