5CH - Interference

Looked at interference today. Interference is caused by two or more waves getting in each others way. When they meet they produce either constructive or destructive interference. What these are is explained in the video. All wave types - sound, light etc. exhibit interference patterns which are made up of alternating lines of constructive and destructive interference.

5CH - Ray diagrams

Applied the refraction formula to drawing/completing ray diagrams today. You can use the refractive index formula along with the knowledge that the angles in a triangle add up to 180 degrees to figure out how light will pass through most objects.

Sometimes we will have to consider the critical angle when completing ray diagrams. If the angle of incidence is greater than the critical angle then the light will reflect. The angle of reflection in these cases is equal to the angle of incidence.

Note: The more observant will spot my mistake with the angles. They should be 54 and 36 not 34 and 56. Final answer is still correct.

5CH - Critical angle and internal reflection

Not all light will be refracted through materials such as glass. Materials like glass have the ability to internally reflect light if the ray is at a certain angle. This is called the critical angle and is the angle beyond which no refraction will take place. In other words, the light will not pass through the material but be reflected back in the original direction of the ray.

Remember that at the precise point of the critical angle, the ray of light refracts into the air at 90 degrees. This is the last refraction that occurs before all light is reflected. Recall also that the angle of incidence is always equal to the angle of reflection.

5CH - Refraction past papers

Practised using the extended refraction formula today. There are three things that change when light enters a more dense material - the direction (angle), the wavelength and the speed. This is reflected in the equation we used today. Remember the more dense medium goes on the bottom of the equation for all values.

Also need to know the differences between blue and red light. Red light refracts less than blue because blue light has a greater refractive index.

5CH - Extended refraction formula

Extended the refraction formula today to include wavelength and velocity. When light moves into a more dense medium, it slows down. Its wavelength also decreases. We can use these changes in velocity and wavelength to calculate refractive index, n.

We also looked at white light refracting through a prism. Red refracts least and violet refracts the most. Because the angles of refraction for the colours that make up white light are different, then it must mean they have different wavelengths and different speeds as they enter the prism. This leads us to the idea that different colours of light have different refractive indexes.

5CH - Refraction

Finished the first lesson on refraction today. It is the refractive index (n) that determines how much refraction occurs. This is expressed as a number with no units. We proved the equation for this and looked at the couple of different ways that the equation can be written. It is very important to make sure that the angle in the least dense medium is 'on the top' of the equation. This is the only way that the refractive index will always be greater than 1.

5CH - Waves

Finished our introduction to waves today. There are two types of wave, most of the ones we will encounter are transverse waves. Frequency, period, amplitude and wavelength should be well understood from Standard Grade.

The various experiments and examples that we will cover in the coming weeks will often refer to 'rays' and 'wavefronts'. Make sure you are okay with these before we move on.

4H - Nuclear power

Nuclear power stations use nuclear fission to generate the heat energy to produce electricity. Neutrons are fired at uranium nuclei causing them to break apart and release energy. This process is called a chain reaction and produces the heat that is used to turn water into steam and drive the turbine that connects to the generator to make electricity.

The main advantage of nuclear fuel is that it produces far more energy than coal, oil or gas. But there are a lot of misconceptions about nuclear power and many people mistrust it, primarily because of its history. The Chernobyl disaster is probably the main reason for this and we'll spend a bit of time looking at this and what caused it to happen.

4H - Generation of electricity

Covered how electricity is generated by using coal, oil and gas. They all work in the same way by using the heat given off by the fuel as it is burned to change water into steam and turn the turbine to generate electricity.

Also looked at hydroelectric power stations as well. They use water released from a height to turn a turbine and generate electricity. A pumped storage hydroelectric power station uses the same technique. Water is pumped back to the reservoir, usually at night when the energy demand is low. The water is then released to help 'boost' the amount of energy available at peak usage times.

3H - Cost of electricity

Having already established that the kilowatt-hour is the unit of energy that we use to pay for our electricity, we went through how to calculate the cost of electricity used. This can be a bit confusing because we have to convert our power rating to kilowatts and our time to hours - this is really the opposite of what we normally do.

There are two types of calculation; the first is just an E=Pt calculation which we have done before but we have to use kilowatts instead of Watts and hours instead of seconds. If we do use Watts and seconds we'll get the answer in Joules which will be a really big number! The second type of calculation is where the cost is taken into account. Here all you do is multiply the number of units (this is the same as saying the number of kilowatt hours) by the price per unit which will always be given in the question.