4 Energy resources and Energy transfers

Question 1

what are the 8 energy stores

Answer 1

chemical
kinetic
gravitational
elastic
themal
magnetic
electrostatic
nuclear

Question 2

what are the 5 energy transfers

Answer 2

mechanically
electrically
radiated sound
ratdiated light
by heating

Question 3

what is the principle of conservation of energy

Answer 3

energy cannot be created or destroyed only transferred from one form to another

Question 4

what is the formula with work, distance moved, force

Answer 4

work = force x distance moved
W = F x d

Question 5

is work done and energy transferred equal

Answer 5

yes

Question 6

what is the formula with gravitiational potential energy, mass, height, gravtiational field strength

Answer 6

gravitiational potential energy = mass x gravitiational field strength x height
GPE = mgh

Question 7

what is the formula for kinetic energy

Answer 7

kinetic energy = 1/2 x mass x speed^2
KE = 1/2mv^2

Question 8

how does conservation of energy produce a link between GPE, KE and work done

Answer 8

if an object falls GPE -> KE and the change in GPE = work done

if an object is thrown up, KE -> GPE and the change in KE = work done

this means that (assuming there is no air resistance) GPE + KE = constant

They are different forms of energy that can be transformed into each other while keeping the total energy constant

Question 9

what is power

Answer 9

the rate of transfer of energy or the rate of doing work

Question 10

what is the formula with work done, time taken, power

Answer 10

power = work done / time taken
P = W / t

Question 11

formula for efficiency

Answer 11

efficiency = useful energy output / total energy output x 100

Question 12

how does thermal energy transfer take place

Answer 12

conduction or convection or radiation

Question 13

how does conduction work

Answer 13

When a substance is heated, the atoms start to move around (vibrate) more
As they do so they bump into each other, transferring energy from atom to atom

Metals are especially good at conducting heat as the delocalised electrons can collide with the atoms, helping to transfer the vibrations through the material and hence transfer heat better

Question 14

how does radioation work

Answer 14

When an object has thermal energy, it emits radiation in the form of electromagnetic waves. The amount and type of radiation depend on the object’s temperature and surface properties.

Question 15

how does convection work

Answer 15

When a fluid (a liquid or a gas) is heated:
The molecules push each other apart, making the fluid expand
This makes the hot fluid less dense than the surroundings
The hot fluid rises, and the cooler (surrounding) fluid moves in to take its place
Eventually, the hot fluid cools, contracts and sinks back down again
The resulting motion is called a convection current

Convection is the main way that thermal energy is transferred through liquids and gases
Convection cannot occur in solids

Question 16

explain how emission and absorption of radiation are related to surface and temperature

Answer 16

black - good absorber and emitter
dull - ok absorber and emitter
white - poor absorber and emitter
shiny - awful absorber and emitter

Question 17

practical: investigate thermal energy transfer by conduction

Answer 17

Attach ball bearings to the ends of each metal strip (different metal) at an equal distance from the centre, using a small amount of wax
The strips should then be turned upside down and the centre heated gently using a bunsen burner so that each of the strips is heated at the central point where they meet
When the heat is conducted along to the ball bearing, the wax will melt and the ball bearing will drop
Time how long this takes for each of the strips and record in a table
Repeat the experiment and calculate an average of each time

Order the metals according to their thermal conductivity
The first ball bearing to fall will be from the rod that is the best thermal conductor
This is because materials with high thermal conductivity heat up faster than materials with low thermal conductivity

Question 18

ways of reducing unwanted energy transfer

Answer 18

To reduce energy transfers by conduction, materials with a low thermal conductivity should be used
Materials with low thermal conduction are called insulators

To reduce energy transfers by convection, convection currents must be prevented from forming
Therefore, the fluid (liquid or gas) that forms the currents must be prevented from moving

The effectiveness of an insulator is dependent upon:
The thermal conductivity of the material
The lower the conductivity, the less energy is transferred

The density of the material
The more dense the insulator, the more conduction can occur
In a denser material, the particles are closer together so they can transfer energy to one another more easily

The thickness of the material
The thicker the material, the better it will insulate

Insulating the loft of a house lowers its rate of cooling, meaning less energy is transferred to the surroundings (outside)
The insulation is often made from fibreglass (or glass fibre)
This is a reinforced plastic material composed of woven material with glass fibres laid across and held together
The air trapped between the fibres makes it a good insulator
The gaps or cavities between external walls are often filled with insulation
This is called cavity wall insulation
This is often done by drilling a hole through the external wall to reach the cavity and filling it with a special type of foam which is made from blown mineral fibre filled with gas
This lowers the conduction of heat through the walls from the inside to the outside

Question 19

practical: investigate thermal energy transfer by convection

Answer 19

Fill the beaker with cold water (not too full) and place it on top of a tripod and heatproof mat
Pick up the crystal using forceps and drop it into the centre of the beaker – do this carefully to ensure the crystal does not dissolve prematurely
Heat the beaker using the Bunsen burner and record observations
Repeat experiment with hot water and record observations

Energy is initially transferred from the Bunsen flame through the glass wall of the beaker by conduction
The water in the region of the Bunsen flame is heated and the space between the water molecules expands, therefore, the water becomes less dense and rises
This causes the dissolved purple crystal to flow upwards with the water
Meanwhile, when the water at the top of the beaker cools, there is less space between the water molecules and the water becomes denser again and falls downwards
The process continues which leads to a convection current where energy is transferred through the liquid
The dissolved purple crystal follows this current which can be clearly observed during this experiment

Question 20

practical: investigate thermal energy transfer by radiation

Answer 20

Set up the four identical flasks painted in different colours: black, grey, white and silver
Fill the flasks with hot water, ensuring the measurements start from the same initial temperature
Note the starting temperature, then measure the temperatures at regular intervals, e.g. every 30 seconds for 10 minutes

All objects emit infrared radiation, but the hotter an object is, the more infrared waves are emitted
The intensity (and wavelength) of the emitted radiation depends on:
The temperature of the body (hotter objects emit more thermal radiation)
The surface area of the body (a larger surface area allows more radiation to be emitted)
The colour of the surface
Most of the energy lost from the beakers will be by heating due to conduction and convection
This will be equal for each beaker, as colour does not affect energy transferred by conduction and convection
Any difference in energy transferred away from each beaker must, therefore, be due to infrared radiation
To compare the rate of energy transfer away from each flask, plot a graph of temperature on the y-axis against time on the x-axis and draw curves of best fit

Question 21

energy transfers involved in generating electricity using wind:

Answer 21

Energy is transferred from the kinetic store of the moving wind to the kinetic store of the turbine as the wind makes it turn. Energy is transferred from the kinetic store of the turbine to the kinetic store of the generator and is transferred electrically to the National Grid.

Question 22

energy transfers involved in generating electricity using water:

Answer 22

electricity is generated in very similar ways, no matter what energy resource is used
A turbine is turned, which turns a generator, which generates electricity
The element that differs is how the turbine is made to turn

Water can be used to turn turbines in the case of hydroelectric dams, tidal barrages and tidal turbines
Energy in the kinetic store of the flowing water is transferred to the kinetic store of the turbine, then to the kinetic store of the generator and transferred electrically to the National Grid

Question 23

energy transfers involved in generating electricity using geothermal:

Answer 23

Water is pumped down to the hot rocks and returns through a fissure as steam which turns the turbine and powers the generator.

Question 24

energy transfers involved in generating electricity using solar heating:

Answer 24

Solar panels use sunlight to heat water in the panel to produce steam which turns a turbine which then turns a generator

Question 25

energy transfers involved in generating electricity using solar cells:

Answer 25

Solar cells, also known as photovoltaic (PV) cells, absorb sunlight. The light energy from the sun is captured by the semiconductor material (usually silicon) in the cells.
Conversion to Electrical Energy: When sunlight hits the semiconductor, it excites electrons, creating an electric charge. This process directly converts light energy into electrical energy.

Question 26

energy transfers involved in generating electricity using fossil fuels:

Answer 26

Fossil fuels can be combusted to heat water, and the steam produced can be used to turn turbines
Energy from the chemical store of the fuel is transferred to the thermal store of the water, which is then transferred to the kinetic store of the turbine, and then transferred to the kinetic store of the generator and then transferred electrically to the National Grid

Question 27

energy transfers involved in generating electricity using nuclear:

Answer 27

Nuclear fuels are reacted to heat water to produce steam that turns turbines
Nuclear store of fuel → kinetic store of fission products -> thermal store of coolant -> thermal store of water → kinetic store of steam -> kinetic store of turbine → electrical of generator

Question 28

advantages and disadvantages of generating electricity by wind

Answer 28

Advantages – renewable, pretty cheap, no atmospheric pollution
Disadvantages – non reliable, not very pretty, uses a large area, location dependent

Question 29

advantages and disadvantages of generating electricity by nuclear

Answer 29

Advantages – very efficient, a little bit of uranium creates a lot of energy, not location dependent, reliable, high energy density, carbon neutral
Disadvantages – creates nuclear waste which is dangerous and can’t be disposed of easily, can be very bad if it explodes

Question 30

advantages and disadvantages of generating electricity by fossil fuels

Answer 30

advantages - reliable and non location dependant
disadvantages - non renewable and creates atmospheric pollution which contributes to global warming

Question 31

advantages and disadvantages of generating electricity by geothermal

Answer 31

Advantages – renewable, reliable, doesn’t contribute to atmospheric pollution.
Disadvantages – location dependent

Question 32

advantages and disadvantages of generating electricity by hydroelectricity

Answer 32

Advantages – very reliable, renewable
Disadvantages – very expensive and time consuming to build, disrupts ecosystem, location dependent

Question 33

advantages and disadvantages of generating electricity by tidal/wave

Answer 33

Advantages – reliable, renewable
Disadvantages – very expensive and time consuming to build, disrupts ecosystem, location dependent

Question 34

advantages and disadvantages of generating electricity by solar heating

Answer 34

Advantages – its renewable, it works all day and it reduces our carbon footprint
Disadvantages – Expensive equipment cost, requires a large area to work, time dependent

Question 35

advantages and disadvantages of generating electricity by solar cells

Answer 35

Advantages – low maintenance, easy to install, reduces carbon footprint, no atmospheric pollution
Disadvantages - Expensive equipment cost, Weather/daytime dependency, not very pretty, takes up large area

Question 36

why does hot air rise

Answer 36

air expands when it is hot causing it to decrease in density so rises