Section 4 b) Summary

The nine types of energy important to learn are:

• Electrical energy
• Light 
• Sound
• Kinetic
• Nuclear
• Thermal 
• Gravitational
• Chemical

Different actions transform energy between the different types, for example a light bulb connected to a battery would be 

Chemical Energy > Electrical Energy > Light Energy 

However, devices such as lights are not 100% efficient. If we look at the light energy emitted compared to the input we can see that a generic light bulb is only 10% efficient, most energy is wasted as heat. 

But if we look at another Sankey diagram, of a more efficient light bulb designed to save energy, only 25% is wasted as heat, it is 75% efficient:

Conduction

Conduction is heat transfer between particles. It occurs mostly in solids, because the particles are more tightly packed than in liquids or gases. Heat flows from an area of warmth to an area of cool, until it is evenly distributed throughout. Metals are good conductors because of their closely packed ions and free moving electrons. Air is a good insulator because the particles are far away, so it is used to insulate frequently. 

Convection 

Convection is a form of heat transfer that only works in a fluid, because it requires free particles to move and create a convection current. 

Convection is when particles are heated, causing them to have more kinetic energy and thus move more and become less dense, causing the hot air to rise. As more hot air rises, it displaces the air that rose before it, forcing the air to move away, and as it does so,  cool, condense, and sink. This is displaced by more sinking air, and forced back to the source of heat, where it will warm and rise again to repeat the cycle. 

An example of convection is a radiator heating a room, as shown in the diagram above. This is also why in a kettle the heating element is at the bottom, it allows convection to occur and heat the water thoroughly. 

Radiation
All objects emit heat through infrared radiation. It doesn't require particles to be transferred, it is transmitted through electromagnetic waves. Radiation and absorption of heat is increased with  bigger temperature difference, or if the object is more matte and black. 

Insulation

In houses, it is important to create insulating layers to limit heat loss through conduction, convection and radiation. 

In people, we have natural mechanisms to insulate heat (goosebumps make hairs stand on end to trap air, but this doesn't do much anymore compared to when humans were hairier), but we use layers of clothing to trap air between which insulates and limits heat loss. 

Section 4 b) Key Words

Chemical energy: Stored energy in chemical form, possessed by food, fuel, batteries, etc.

Conduction: Energy transfer directly through an object where there is a difference in temperature.

Conserved: When energy is transferred from one form to another it is conserved; none is lost/destroyed.

Convection: The transfer of energy in a convection current through a fluid wherein warm material becomes less dense and rises and cool air becomes more dense and sinks.

Efficiency: How much energy is useful compared to how much is wasted.

Electrical energy: Energy wherein a current is flowing.

Insulation: An insulating material placed between cold and warm areas to limit energy transfers.

Kinetic energy: Anything that is moving has kinetic energy, also called movement energy.

Light energy: Energy emitted in the form of light, from the Sun, light bulbs, etc.

Nuclear energy: Energy released from nuclear reactions (e.g. atomic bombs)

Potential energy: Energy that is stored elastically or gravitationally. The object has been stretched or placed higher, giving it the potential to move.

Radiation: Energy transferred through infrared radiation. All objects have it and constantly emit and absorb it to match the surroundings.

Sankey diagram: A diagram used to show input and output of energy, a visual aid to see the efficiency of something.

Sound energy: Energy from vibrations emitted in sound waves.

Thermal energy: Heat energy, emitted from something hot and absorbed by something cold.

Section 4 b) Specification

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

Thermal > Light = a very hot object
Thermal > Kinetic = steam engine
Light > Chemical = a tree
Electrical > Thermal = an electric fire
Electrical > Light = a light bulb
Electrical > Kinetic = an electric motor
Electrical > Sound = a loudspeaker
Sound > Thermal = a sound-absorbing cloth
Sound > Electrical = a microphone
Kinetic > Sound = hitting a drum
Kinetic > Thermal = friction
Kinetic > Electrical = a dynamo
Chemical > Light = a glow worm
Chemical > Thermal = a gas fire
Chemical > Electrical = a battery
Chemical > Kinetic = leg muscles
Chemical > Elastic = pulling a catapult
Nuclear > Light = an atom bomb
Nuclear > Kinetic = an atom bomb
Nuclear > Thermal = an atom bomb
Nuclear > Sound = an atom bomb
Elastic > Kinetic = releasing a catapult
Elastic > Gravitational = releasing a catapult
Gravitational > Kinetic = a falling object

4.3 understand that energy is conserved

When energy is transferred or transformed, none of it is lost. Some energy is always wasted, leaving in a different form (e.g. light bulbs heat up as well as lighting up)

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

The relationship should be multiplied by 100 to give the percentage of efficiency so it can be compared to different devices.

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

Most electrical devices lose energy as heat. For example in a light bulb, the useful energy is the light energy, and the waste is heat. A normal, inefficient light bulb would have a Sankey diagram that looked something like this:

The curved arrows are used to show waste energy, while the straight arrows show useful energy. You can see in this diagram that this light bulb is only 10% efficient, which is extremely wasteful. So, efficient, energy-saving light bulbs have been developed. Their Sankey diagrams look more like this:

You can see in this the straight arrow is much bigger than the curved arrow. This light bulb is 75% efficient, enormously better than the first bulb.
In drawing a Sankey diagram, it is important to keep the widths of the arrows proportional.

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

Conduction is the transfer of energy through a substance without the substance itself moving. Metals are good conductors because of their close together ions and free electrons that can transfer energy. Gases are poor conductors because the particles are far apart and it takes longer for energy to travel through them. Heat is conducted more quickly if the conductor is shorter in length, bigger in cross-sectional area, and the temperature difference is greater.

Convection is when particles are heated, causing them to have more kinetic energy and thus move more and become less dense, causing the hot air to rise. As more hot air rises, it displaces the air that rose before it, forcing the air to move away, and as it does so,  cool, condense, and sink. This is displaced by more sinking air, and forced back to the source of heat, where it will warm and rise again to repeat the cycle. This creates a convection current (convection only works in a fluid)

Radiation involves the emission of electromagnetic waves (like the infrared waves in a toaster). All objects are continuously emitting and absorbing thermal radiation. If an object is hotter than its surroundings it will emit more, and if it is cooler it will absorb more; an icecube will melt and hot coffee will cool in the same temperature environment. This continues until the temperature is constant throughout all substances. This is the only form of heat transfer that doesn't involve particles and therefore can happen through a vacuum. Radiation is best both emitted and absorbed by matte black surfaces.

4.7 explain the role of convection in everyday phenomena

Convection is used in many everyday situations, e.g. heating a room with a radiator, in a kettle, boiling water on the stove, in insulating (by creating tiny pockets of air, each containing its own convection current, the energy is not easily transferred out), etc.

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

In the home:

• Thick curtains: Trap a layer of air between windows and warm rooms, preventing hot air from reaching the glass through convection and conduction. 
• Cavity wall insulation limits radiation through the walls, as well as conduction and convection. 
• Double glazed windows have a layer of dry air between them that acts as an insulator between the cold, outside glass and the warm inside glass, limiting heat loss through conduction, convection and radiation.
• Carpets/rugs, especially with underlay, trap air and create a layer of insulation between the colder ground and the rest of the room
• Draught-proofing reduces heat loss through convection.
• Loft and roof insulation prevent heat loss through convection as the hot air rises. 

Humans:

• Goosebumps in cold weather cause hairs to stand on end to trap air and provide a layer of insulation to the body
• More layers of clothing create layers of air between each item, which insulates the body. 
• Fabric absorbs some of the radiation from the body, reducing heat loss. 

Section 4 a) Specification

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).

Kilograms measure mass
Joules measure energy
Metres measure distance
Metres/Second measure velocity
Metres/Second2 measure acceleration
Newtons measure weight
Seconds measure time
Watts measure power

Section 4 Specification

Section 4: Energy resources and energy transfer

a) Units

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).


b) Energy transfer

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

4.3 understand that energy is conserved

4.4 know and use the relationship:

efficiency = useful energy output / total energy input

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

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

4.7 explain the role of convection in everyday phenomena

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


c) Work and power

4.9 know and use the relationship between work, force and distance moved in
the direction of the force:
work done = force × distance moved
W = F × d

4.10 understand that work done is equal to energy transferred

4.11 know and use the relationship:
gravitational potential energy = mass × g × height
GPE = m × g × h

4.12 know and use the relationship:
kinetic energy = 1/2 x mass x speed2
KE = 1/2 x m x v2

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

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

4.15 use the relationship between power, work done (energy transferred) and
time taken:
power = work done / time taken
P = W / t


d) Energy resources and electricity generation

4.16 describe the energy transfers involved in generating electricity using:

• wind 
• water 
• geothermal resources
• solar heating systems
• solar cells
• fossil fuels 
• nuclear power

4.17 describe the advantages and disadvantages of methods of large-scale electricity production from various renewable and nonrenewable resources

Section 3 d) Summary

Waves can be reflected, refracted and diffracted, whether they're transverse or longitudinal.

Sound waves can be measured using a device called an oscilloscope and a microphone. The microphone is connected into the oscilloscope, a sound made, and from the tracing made the frequency, amplitude, time period and wavelength can be calculated.
Louder sounds have a higher amplitude, and more high-pitched sounds have a higher frequency.

Reflection
The law of reflection says that the angle of incidence = the angle of reflection

i = r

This principle can be applied to a phenomenon known as Pepper's ghost, where lights and reflections are used to project a virtual image.

One light shines onto the background, lighting it up so the viewer can see it through the glass. The other light shines onto an image, hidden from view. The light is reflected off of this image, and travels to the glass, where it is reflected and the viewer sees it. The reflection merges with the background, so appears to be there and not just a reflection. This is called a virtual image.
This concept can also be demonstrated in a more simple manner:

The glass is equidistance from the candles, so when the light from the front candle is reflected it appears to be on the unlighted candle.

Sound experiment:

1. Measure 100 metres from a wall, and stand there and clap with clapping blocks. Every time you hear the echo of the previous clap, clap again.
2. Once you have a steady rhythm, time how long it takes for the time periods of 10 claps (count 11 claps) 
3. Divide this time by 10 to find the time for 1 clap, then divide double the distance (200 m) by this number (you must double it because the wave travels the distance to the wall and back).

This will give you the speed of sound in air, but is also affected by human reaction times so will not give a totally accurate result.

Total internal reflection (finding the critical angle):

1. Shine a ray into a semi circular prism (this is ideal, because you can shine at the mid-point of the flat side without being refracted the first time due to the shape having normals at all angles)
2. Shine it at the mid-point from a range of different angles, starting with a smaller angle of incidence, and gradually moving it around, until the ray is in line with the flat edge. This is the critical angle: the last point at which the light is reflected. 
3. Once the angle is greater than the critical angle, it will become totally internally reflected. 

Critical angle can be calculated with this formula: sin c = 1 / n 

Total internal reflection is useful in optic cables among other things. It allows the information to be transferred long distances without being lost, all of the light is reflected. This concept is also used in jewellery and cutting jewels such as diamonds. By creating total internal reflection, they reflect light more and are more 'sparkly'. 

Refraction

Refraction is when the direction of a wave changes as it changes from one medium to another.
You can see this when you put a straw in water, it appears bent or broken.

We can see how different objects and media refract objects through investigations.

Finding the refractive index of glass
1. Using a rectangular glass block, and trace its outline onto a piece of paper. Create a series of lines to create different angles about a normal.
2. Shine a line/ray of light from a ray box along each line, and mark the emergent line with two x's, and connect the line to the normal, and then to the angle of incidence.
3. Measure each of the angles of refraction in comparison to the angle of incidence, and use
n = sin i / sin r
for each, and find the average of n to try to erase inaccuracies.

This same experiment can be done with different shaped blocks to see how this affects it, or different media (e.g. plastic)


Diffraction

Diffraction is the spread of waves beyond a barrier. This can be seen with waves at the beach, after passing through a gap

This effect happens in the same manner with sound and light waves. For example, when a door is opened into a dark room, we see the light spread.
 

Diffraction is increased when the ratio of gap size to wavelength is balanced so the gap size is smaller and the wavelength is larger.

Diffraction doesn't just happen through gaps, though, it also happens when passing an edge.

Signals: Analogue vs. Digital

Signals can be digital or analogue, the difference being that analogue has continuous variables and digital having two fixed settings, on and off or 0 and 1.

Advantages and disadvantages:

• Digital signals have a wider bandwidth and can carry more information
• Digital can be more easily restored if distorted
• Analogue signals are near impossible to restore if badly distorted. 
• Analogue signals have an infinite range of data
• Analogue signals are easy to process
• Analogue signals are easily distorted
• Digital signals travel faster
• Digital signals are more complicated to process. 

Section 3 d) Key Words

Amplitude: The distance between the crest of a wave and the neutral point 0. Larger amplitudes mean louder sounds (in sound waves)

Analogue signal: A signal that continuously varies. It is easily distorted and difficult to restore.

Angle of incidence: The angle at which a wave changes from one medium to another, compared to the normal.

Angle of refraction: The angle at which a wave is refracted from the perpendicular surface.

Bandwidth: The frequency of a wave. Digital signals have wider bandwidths, meaning they can carry more information at once.

Critical angle: The angle at which the wave is no longer refracted, but changes to becoming reflected.

Diffraction: When a wave passes an object and spreads beyond it. Its effect is affected by the wavelength in proportion to the size of the gap/blockage. If the gap is smaller in proportion to a larger wavelength, the effects of diffraction are greater.

Digital signal: A signal with only two settings, 0 and 1. It is easily restored and has a larger bandwidth than an analogue signal, so it is able to carry more information.

Frequency: How many times a wave is completed in one second.

Longitudinal waves: Waves that oscillate in the direction of travel. Sound waves are longitudinal.

Oscillation: The vibration. One wave.

Oscilloscope: A machine that measures the vibrations of a wave and creates a trace.

Pitch: How high or low a sound is. A flute makes a high-pitched noise, whereas a double bass makes a low-pitched noise.

Plane mirror: A completely flat mirror.

Reflection: When waves bounce off a surface they are reflected.

Refraction: The change in direction of waves after passing from one medium to another.

Refractive index: The refractive index of a medium tells us how much it will refract light waves. It can be found by this formula: n = sin i / sin r

Total internal reflection: When all waves are reflected inside a medium, none are refracted.

Transverse waves: Waves that oscillate perpendicular to the direction of travel. Light waves are transverse.

Virtual image: An image that is not real, it is a projection or reflection.