P2 - Sustainable Energy Flashcards
In which different forms can energy be
stored?
Chemical, nuclear, kinetic, gravitational,
elastic, thermal, electrostatic and
electromagnetic.
How is energy transferred from one form
to another?
By working or heating.
What form of energy is stored in
batteries?
Chemical energy.
How are electrical appliances supplied
with energy?
Chemical potential in batteries or fuels is transferred to electrical energy (producing electrical current) in wires, which do work on devices such as motors and heaters.
Why is electricity a convenient way to
transfer energy?
It is easily transmitted across large
distances, and can be used to do work in
a variety of ways
What is the principle of conservation of
energy?
Energy cannot be created or destroyed;
it can only be transferred from one form
into another.
How and why is energy wasted?
When energy is used to do work, energy is
dissipated into forms other than the desired
outcome. For example, light bulbs sometimes
emit heat energy. It is dissipated into the
surroundings, into inaccessible thermal stores.
What is the power of an appliance?
A measure of the amount of energy it
transfers per second (i.e. its rate of
energy transfer).
What is the unit of power?
Watt (W)
This is equivalent to 1 Joule per second
(J/s).
What is the equation for power?
Power = energy ÷ time
What is a system?
An object or group of objects.
What is a closed system?
A closed system is one in which no
energy is transferred into or out of the
system. There is no net change to the
energy of the system.
How can “wasted” (thermal) energy be
reduced?
Thermal insulation prevents thermal
energy from being lost from a system.
An example of this is double glazing in
houses, to conserve energy produced by
heating appliances.
How can “wasted” energy in a motor be
reduced?
Lubrication; applying oil to a motor
reduces friction so less energy is lost
overcoming friction.
What is thermal conductivity?
A measure of a material/object’s ability to
conduct heat.
What does a high thermal conductivity
mean?
The higher the thermal conductivity, the more easily heat is transmitted through the material. This results in a higher rate of energy transfer via conduction across the material.
How does thermal conductivity apply to
buildings?
The lower the thermal conductivity of the walls, the less easily heat is lost. Insulating materials are useful as they have a low thermal conductivity, so they retain heat and therefore conserve
energy.
What is efficiency?
The ratio of useful work done to energy supplied. It is often given as a percentage, i.e. the percentage of energy which is converted to a useful form.
Give the equation for efficiency
Efficiency =
Useful energy output / Total energy input
You can convert this to a percentage by
multiplying the answer by 100
How can the efficiency of a system be
increased?
- Reducing waste output (by lubrication,
thermal insulation etc). - Recycling waste output (eg. recycling
thermal waste energy as input energy).
Name a diagram used to illustrate
energy transfers
Sankey diagram
What does a Sankey diagram show?
All of the energy transfers in a system,
including energy wasted/dissipated to
surroundings.
How is a Sankey diagram useful?
It can be used to calculate the efficiency
of energy transfers.
Describe the features of a Sankey
diagram
● Arrows point in the direction of transfer of energy. ● The width of lines/arrows is proportional to the amount of energy transferred.
What are the main energy resources
available to humans?
Fossil fuels (oil, gas and coal), nuclear
fuels, biofuels, wind, hydroelectricity,
tides and solar energy.
Define renewable energy
Energy which can be replenished from a
source which does not run out.
Which energy sources are
non-renewable?
● Fossil fuels
● Nuclear fuel
Which energy sources are renewable?
● Biofuels ● Wind ● Hydroelectric and tidal energy ● Geothermal energy ● Solar power
Why is non-renewable energy used to
provide electricity on a large scale?
Non-renewable sources tend to have a
larger energy output per kilogram of fuel.
How is electricity generated in power
stations?
By spinning a magnet near a wire, a
voltage is induced in the wire. The
voltage results in an electrical current.
Explain the mechanism of electricity
production in power stations
Water is heated (using energy from
sources such as fossil fuels), causing it
to evaporate into steam which rises and
spins a turbine which is connected to a
generator, therefore producing electricity.
Define and give units for voltage
The potential difference which causes
current to flow in a circuit. Voltage is
measured in Volts, V.
Define and give units for current
Current is defined as the rate at which
charge flows around a circuit. It is
measured in Amperes, A.
Define alternating current
A current that changes direction regularly
(depending on its frequency). A 50Hz
alternating current changes direction 50
times a second.
Define direct current
Direct current is a movement of charge
in one direction only (i.e. only positive or
only negative).
Give examples of direct current
● Cells
● Batteries
Give an example of alternating current
Mains electricity provides an alternating
current.
Give the key features of mains electricity
in the UK
● Alternating current of frequency 50Hz
● 230 V
How does electricity in the National Grid
differ from mains supply?
Electricity is transported in the National
Grid at much higher voltages to reduce
energy loss.
How is the voltage of electricity altered?
(eg. for transport across the National
Grid)
Using transformers. The voltage is
increased for travelling long distances.
What is a step up transformer?
A transformer which increases voltage
(decreasing the current).
These are used in the National Grid to
increase p.d. to a high value for
transport.
What is a step down transformer?
A transformer which decreases the
voltage (increasing the current).
These are used to decrease p.d. from
the national grid for domestic use.
Name the wires are in a typical
plug/appliance?
- Live
- Neutral
- Earth
Describe the live wire (and give its
voltage)
The live wire is brown and carries 230V.
What is the purpose of the live wire?
It carries alternating potential difference
from the supply to the appliance.
Describe and give the voltage of the
neutral wire
The neutral wire is blue and carries 0V.
What is the function of the neutral wire?
It completes the circuit.
Describe and give the voltage of the
earth wire
The earth wire has green and yellow
stripes and carries 0V.
What is the purpose of the earth wire?
It is a safety wire, preventing the
appliance from becoming live with static
electricity.
How does the earth wire work?
The earth wire is connected to both the earth and the
appliance casing. If the live wire touches the casing,
the appliance becomes live, which will cause electric
shocks if touched. The earth wire instead transfers
the current to the ground, discharging the casing of
the appliance so it does not become live.
Describe the projected trend of energy
uses and why this is problematic
Energy use has been, and is projected to continue to be, increasing since the industrial revolution. This is problematic because of finite resources running out (non-renewable fuels).
