Energy - Topic 1 Flashcards
what is a system
an object or group of objects
what happens when a system changes?
energy is transferred, can be transferred into or away from system, between different objects in the system or between different energy stores
what are the 8 energy stores
-thermal
-kinetic
-gravitational potential
-elastic potential
-chemical
-magnetic
-electrostatic
-nuclear
How can energy be transferred?
mechanically - by a force doing work
electrically - work done by moving charges
by heating
by radiation
energy transfer of boiling water in kettle
energy transferred to water by heating, into the waters thermal energy store causing temp of water to rise.
what is the specific heat capacity of a substance?
the amount of energy needed to raise the temperature of 1kg of a substance by 1 degree.
units of specific heat capacity
joules/degrees Celsius/kilogram
what is the conservation of energy?
energy is never created or destroyed only transferred.
what is dissipated energy
energy that is being stored in a way that is not useful, sometimes called wasted energy
what is a closed system
systems that where neither matter nor energy can enter or leave. the net change in the total energy of a closed system is always 0
definition of power
the rate of energy transferred or the rate at which work is done.
unit of power
watts
two motors lift the same mass through the same height. motor a does this in half the time of motor b which motor dissipates the most energy?
motor a, the energy transferred is the same but the time taken is less, p=e/t
describe energy changes when a ball is thrown upwards then returns to its starting position.
- upwards KE is converted to GPE
-Peak: Maximum GPE no KE
-downwards GPE converted to KE
examples of chemical energy stores
-food
-fuel
-batteries
describe energy changes in a filament light bulb
-electrical energy transferred into heat and light energy
-light energy is useful, heat energy is waste energy.
how can the efficiency of a system be increased?
-reducing waste output (by using lubricant or thermal insulation)
-recycling waste output
what is conduction?
the process where vibrating particles transfer energy to neighbouring particles.
do double glazed windows have higher or lower thermal conductivity than single glazed?
lower meaning less energy is transferred though them
what factors effect the rate of cooling a building
-thickness of the walls
-thermal conductivity of the walls
three methods of reducing heat loss from a building
-double glazing
-loft and wall insulation
-thicker walls
how can the efficiency of a mechanical machine with moving parts be improved
lubricate any moving parts to reduce the friction and therefore reduce energy loss due to heating
what is a non-renewable energy source? Give examples.
- they will run out one day
-cause damage to environment
-e.g coal, oil, natural gas
what is a renewable energy source? give examples
-will never run out can be renewed as they are used.
-don’t provide as much energy and some are unreliable because they depend on the weather.
-e.g sun, wind, bio-fuels,tides and geothermal
environmental impacts of burning fossil fuels
-carbon dioxide contributes to the green house effect and cases global warming.
- sulphur dioxide leads to acid rain which can damage buildings and crops
3 advantages of using fossil fuels as energy sources
-reliable: not dependant on external factors
-can produce large amounts of energy for a given quantity.
-still relatively abundant so cost effective.
two disadvantages of using renewable energy sources to generate power.
-output is often determined by external factors (e.g wind) so supply uncertain.
-generating power through other means is often more efficient and economically beneficial.
three advantages of nuclear power
- very large amounts of energy for relatively small quantities of fuel.
- don’t release greenhouse gases so don’t contribute to climate change.
-low fuel cost
three disadvantages of nuclear power
- produces nuclear waste which is harmful to humans and must be stored safely for centuries.
- non- renewable energy source
- risk of nuclear accidents which have fatal consequences on humans and environment.
how does hydroelectric power produce energy?
- rain water collects behind a dam
- when this water is released it is used to turn a turbine.
- This turbine turns a generator which produces electricity.
disadvantages of hydroelectric power
- dam may cause flooding
- it can cost a lot to install the required infrastructure
disadvantages to biofuels
- when plants are burned they relsease co2
- in order to grow biofuels you need to destroy land this causes problems because the land could have been a natural habitat or it might have involved burning or destroying plants which releases co2
- growing biofuels reduces land available to grow food.
advantages of tidal energy sources
- don;t produce greenhouse gases.
- reliable as tides happen twice a day
- cheap to run as tides are natural.
advantages of solar pannels
-don’t cause harm to the environment
- renewable energy source
- can be used in remote areas where other types of energy are less acsessable.
what is the definition of power?
-the rate at which energy is transferred or the rate at which work is done.
equation for kinetic energy
0.5 x mass x (speed)2
equation for elastic potential energy
0.5 × spring constant × (extension)2
equation for gravitational potential energy
mass × gravitational field strength × height
equation for change in thermal energy
= mass × specific heat capacity × temperature change
give two equations for power
energy transferred/time -p = e/t
and
work done/time - p=w/t
describe energy transferrs for a bungee jumper
- when falling the GPE is converted to KE of the jumper.
- As the chord tightens, KE is converted and stored as Elastic potential Energy.
- At the lowest point the jumpers initial GPE = The EpE store in the chord
Explain why the bungee jumper slows down as the chord begins to stretch
-Kinetic energy decreases since it is converted to elastic potential energy.
- since KE is proportional to (velocity)2 as KE decreases so does velocity
give 2 equations to calculate efficiency
- =useful power output energy transfer/ total input energy transfer.
- = useful power output/total power output.
