P1 - Energy Flashcards
What are Energy stores?
Energy can be stored in different ways, and there are changes in the way it is stored when a system changes
What does the principle of energy state and explain what it means?
Energy can be stored in different ways, and there are changes in the way it is stored when a system changes
The principle of conservation of energy states that:
Energy cannot be created or destroyed, it can only be transferred from one store to another
This means that for a closed system, the total amount of energy is constant
What are all the different Energy stores?
- There are many stores of energy, including:
- magnetic
- internal (thermal)
- nuclear
- chemical
- kinetic
- electrostatic
- elastic potential
- gravitational potential
What is the magnetic Energy store?
Magnetic
The energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart.
Examples: Fridge magnets, compasses, maglev trains which use magnetic levitation.
What is the Thermal Energy store?
Internal (thermal)
The total kinetic and potential energy of the particles in an object, in most cases this is the vibrations - also known as the kinetic energy - of particles. In hotter objects, the particles have more internal energy and vibrate faster.
Human bodies, hot coffees, stoves or hobs. Ice particles vibrate slower, but still have energy.
What is the chemical Energy store?
The energy stored in chemical bonds, such as those between molecules.
Examples:
Foods, muscles, electrical cells.
What is the Kinetic Energy store?
The energy of a moving object.
examples:Runners, buses, comets.
What is the Electrostatic Energy store?
The energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart.
Thunderclouds, Van De Graaff generators.
What is Elastic potential energy?
Examples of of Elastic: Drawn catapults, compressed strings, inflated balloons
The energy stored when an object is stretched or squashed.
What is Gravitational Potential Energy?
The energy of an object at height above a ground.
Examples: Aeroplanes, kites, mugs on a table
What is Nuclear Energy?
The energy stored in the nucleus of an atom.
Examples:Uranium nuclear power, nuclear reactors.
What are the four ways of transferring energy?
- A system can change between stores through different energy transfer mechanisms
- Examples of these are:
- Mechanical
- Electrical
- Heating
- Radiation
Give an example of Thermal Energy transfer
- An example of a thermal energy transfer is a hot coffee heating up cold hands
What is energy?
Energy is a property that must be transferred to an object in order to perform work on or heat up that object
What is a System?
- Energy will often be described as part of an energy system
- In physics, a system is defined as:
An object or group of objects
What is an Open, Isolated and Closed system?
- Therefore, when describing the changes within a system, only the objects or group of objects and the surroundings need to be considered
- A thermodynamic system, for example, can be isolated, closed or open
- An open system allows the exchange of energy and matter to or from its surroundings
- A closed system can exchange energy but not matter to or from its surroundings
- An isolated system does not allow the transfer of matter or energy to or from its surroundings
What is a Transfer diagram?
Gravitational energy stored in the child at the top of the slide is transferred as mechanical work done to speed up and to do work against friction. The result of this is a shift of energy from gravitational potential energy to kinetic energy and internal energy (raising the temperature of the child and the slide).
What are sankey diagrams?
Sankey diagrams start off as one arrow that splits into two or more points. This shows how all of the energy in a system is transferred into different stores.
Sankey diagrams are really useful when the amount of energy in each of the energy sources is known. The width of the arrow is drawn to scale to show the amount of energy.
What is Energy dissipation?
o system is perfect. Whenever there is a change in a system, energy is transferred and some of that energy is dissipated.
Dissipation is a term that is often used to describe ways in which energy is wasted. Any energy that is not transferred to useful energy stores is said to be wasted because it is lost to the surroundings. Electrical cables warming up are a good example of this. It is not useful to have hot wires behind a television as energy is dissipated to the surrounding air.
In a mechanical system, energy is dissipated when two surfaces rub together. Work is done against friction which causes heating of the two surfaces - so the internal (thermal) energy of the surfaces increases. Adding lubricant between the surfaces reduces this friction and so less heat is wasted, like on a conveyor belt for example.
In an electrical context, new types of components can be more energy-efficient. For example, using LED light bulbs as opposed to filament lamps causes less energy to be wasted.
Give Examples of dissapation
Energy is usually lost by heating up the surroundings though sometimes energy is dissipated as sound waves.
The ways in which energy is dissipated depends on the system:
- for a radio or set of speakers, the electrical work is transferred into useful sound waves and infrared radiation is dissipated - ie wasted as heat energy
- for a tumble dryer, the electrical work is transferred into useful internal (thermal) energy which helps to dry clothes - energy is dissipated by sound waves
What is Kinetic Energy?
- The kinetic energy (Ek or KE) of an object (also known as its kinetic store) is defined as:
The energy an object has as a result of its mass and speed
- This means that any object in motion has kinetic energy
How do you calculate Kinetic Energy?
- Kinetic energy can be calculated using the equation:
Ek = ½ × m × v2
- Where:
- Ek = kinetic energy in Joules (J)
- m = mass of the object in kilograms (kg)
- v = speed of the object in metres per second (m/s)
What is The gravitational potential energy (Ep or GPE) of an object (also known as its gravitational store) is defined as:
The energy an object has due to its height in a gravitational field
- This means:
- If an object is lifted up it will gain Ep
- If it falls, it will lose Ep
Gravitational Potential Energy?
How do you calculate Gravitation Potential Energy?
- The Ep of an object can be calculated using the equation:
Ep = m × g × h
- Where:
- Ep = gravitational potential energy, in Joules (J)
- m = mass, in kilograms (kg)
- g = gravitational field strength in Newtons per kilogram (N/kg)
- h = height in metres (m)
What is the gravitational Field Strength and how does it differ across plantets?
- The gravitational field strength (g) on the Earth is approximately 10 N/kg
- The gravitational field strength on the surface of the Moon is less than on the Earth
- This means it would be easier to lift a mass on the Moon than on the Earth
- The gravitational field strength on the surface of the gas giants (eg. Jupiter and Saturn) is more than on the Earth
- This means it would be harder to lift a mass on the gas giants than on the Earth
What is Elastic potential Energy?
- When a spring is stretched (or compressed), work is done on the spring which results in a transfer of energy to the spring’s elastic store
- Elastic potential energy is defined as:
The energy stored in an elastic object when work is done on the object
- This means that any object that can change shape by stretching, bending or compressing (eg. springs, rubber bands) can store elastic energy
How do you calculate Elastic Potential Energy?
- The amount of elastic potential energy stored in a stretched spring can be calculated using the equation:
Ee = ½ × k × e2
- Where:
- Ee = elastic potential energy in Joules (J)
- k = spring constant in Newtons per metre (N/m)
- e = extension in metres (m)
- The above equation assumes that the spring has not been stretched beyond its limit of proportionality
What happens when a vertical spring is extended and contracted?
What forms of energy are transferred?
- When a vertical spring is extended and contracted, its energy is converted into other forms
- Although the total energy of the spring will remain constant, it will have changing amounts of:
- Elastic potential energy (EPE)
- Kinetic energy (KE)
- Gravitational potential energy (GPE)
- When a vertical mass is hanging on a spring and it moves up and down, its energy will convert between the three in various amounts
How does the energy stores differ across these three springs?
- At position A:
- The spring has some EPE since it is slightly compressed
- Its KE is zero since it is stationary
- Its GPE is at a maximum because the mass is at its highest point
- At position B:
- The spring has some EPE since it is slightly stretched
- Its KE is at a maximum as it passes through its resting position at its maximum speed
- It has some GPE since the mass is still above the ground
- At position C:
- The spring has its maximum EPE because it is at its maximum extension
- Its KE is zero since it is stationary
- Its GPE is at a minimum because it is at its lowest point above the Earth’s surface
What is Thermal Energy?
How do you calculate specific Heat capacity?
- Thermal energy is the energy contained within a system that is responsible for its temperature
- This energy can also be stored in or released from the system
- The amount of thermal energy needed to raise the temperature of a given mass by a given amount can be calculated using the equation:
ΔE = mcΔθ
- Where:
- ΔE = change in thermal energy, in joules (J)
- m = mass, in kilograms (kg)
- c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)
- Δθ = change in temperature, in degrees Celsius (°C)
- The specific heat capacity of a substance is defined as:
The amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C
What does it Mean if a substance has a high or low specific heat capacity?
- Different substances have different specific heat capacities
- If a substance has a low specific heat capacity, it heats up and cools down quickly (ie. it takes less energy to change its temperature)
- If a substance has a high specific heat capacity, it heats up and cools down slowly (ie. it takes more energy to change its temperature)
What Energy Transfers happen when an object is projected upwards?
- Before the ball is thrown upwards, the person holding the ball is a store of chemical energy
- When the ball is thrown, the chemical energy is converted into kinetic energy as the ball begins to move upwards
- As the height of the ball increases, the kinetic energy is converted into gravitational potential energyes
What energy transfer happen when A Moving Object is Hitting an Obstacle
- When an object, such as a car, is moving, chemical energy from the fuel is converted into kinetic energy
- If the object hits an obstacle, such as a car hitting a wall, the speed of the car will decrease very quickly
- Therefore, the kinetic energy of the car will decrease
- *es**
- In this scenario, most of the kinetic energy is converted to heat and sound between the car and the wall
What energy transfer happen when A Vehicle Being Accelerated by a Constant Force
- When a vehicle is stationary, it stores chemical energy in the fuel
- When the vehicle speeds up, or accelerates, the chemical energy is converted into kinetic energy
What energy transfers happen when a vehicle is slowing down?
- When a vehicle is moving, it has kinetic energy
- As it slows down, or decelerates, the kinetic energy is converted to heat and sound between the tyres and the road
What energy transfers happen when water boils in a Electric kettle?
- When an electric kettle is used to heat up water it uses electricity to increase the temperature of the heating element
- During this process, electrical energy is converted into heat energy
What Energy changes happen during Heating?
- Heating changes the energy stored within a system by increasing the energy of the particles that make up that system
- This either raises the system’s temperature or, produces a change of state (eg. solid to liquid)
- An example of the energy change by heating is electrical energy to thermal energy
What Energy changes happen when work is done by forces?
- Work is done when energy is transferred from one store to another
- When a force causes an object to move, work is done against frictional forces, causing the object’s temperature to increase and energy is lost as heat and sound to the surroundings
- For example, a person warms up his hands by repeatedly rubbing them together
- An example of the energy change by work done by forces is kinetic energy to thermal energy
What energy changes happen when current flows around a circuit?
- Current is the flow of charge
- A current flows when there is a potential difference applied to the circuit
- This is provided by the power supply or a cell
- This gives each charge an amount of energy
- This is the work done by the power supply when a current flows
- An example of the energy change by work done when a current flow is chemical energy to electrical energy to thermal energy
What is Power?
- Machines, such as car engines, transfer energy from one type to another every second
- The rate of this energy transfer, or the rate of work done, is called power.
How do calculate Power?
- Power is defined as the energy transferred per unit time:
Power = Energy Transferred/Timees
- Power can also be defined as the work done per unit time:
Power = Work done/Time
- The energy transferred, or work done, is always in units of joules (J)
- Time is measured in seconds (s)
- Power, P is measured in the units watts (W)
- 1 Watt = 1 Joule per second
How do you compare power outputs?
An example that illustrates the definition of power is by comparing two electric motors if:
- They lift the same weight
- They are lifted by the same height
- One lifts it faster than the other
- The motor that lifts the weight faster is said to have more power
- This is because the same work is done in a shorter amount of time
What are the Energy changes in Television?
- The energy changes in televisions are:
electrical energy ➝ light energy + sound energy + thermal energy
- Light and sound energy are useful energy transfers whereas thermal energy (from the heating up of wires) is wasted
What are the energy changes in a heater?
- The energy changes in an electrical heater:
electrical energy ➝ thermal energy + sound energy + light energy
- In a gas cooker, the energy transfers are similar but the initial source of energy is different:
chemical energy ➝ thermal energy + sound energy + light energy
- In both these cases, thermal energy is useful, whereas sound and light are not
What are the Energy changes in a rollercoaster?
- A rollercoaster increases its speed as it travels down a steep section of track and gains kinetic energy (KE)
- When the rollercoaster travels up a steep section of track, this kinetic energy is transferred into gravitational potential energy (GPE)
- These energy changes happen several times during a rollercoaster ride as the track goes up and down and around
- As the rollercoaster in the diagram travels from A to D, the energy changes that take place are:
GPE ➝ KE ➝ GPE ➝ KE
- Some energy is transferred to the surroundings as heat and sound energy too
- At point A:
- The rollercoaster is raised above the ground, therefore it has GPE
- As it travels down the track, GPE is converted to KE and the roller coaster speeds up
- At point B:
- KE is converted to GPE as the rollercoaster rises up the loop
- At point C:
- This GPE is converted back into KE as the rollercoaster travels back down the loop
- At point D:
- The flat track means the rollercoaster only has KE
What are the Energy changes when jumping on a Trampoline??
- When jumping on a trampoline the energy changes are:
elastic potential energy ➝ kinetic energy ➝ gravitational potential energy
- Some energy is transferred to the surroundings as heat and sound energy too
What is thermal Conductivity?
- Conduction is the process of heat (or electricity) being directly transmitted through a material of a substance when there is a temperature difference
- The direction of heat transfer is always from hot to cold
- The thermal conductivity of a material is a measure of its ability to conduct heat
The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across the material
- Materials with high thermal conductivity heat up faster than materials with low thermal conductivity
- Examples of substances with high thermal conductivity include:
- Diamond
- Aluminium
- Graphite
- Examples of substances with low thermal conductivity include:
- Air
- Steel
- Bronze
How do Cavity walls and loft insulation work?
- nsulating the loft of a house lowers its rate of cooling, meaning less heat is lost to the 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
- It has a much lower thermal conductivity than the roof material
- Several layers make it very thick and therefore decrease the rate of cooling
- Another aspect that affects the cooling of buildings is the walls
- Houses in cold countries are fitted with cavity wall insulation 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
How do you calculate efficiency?
What are the main uses of energy resources?
- The three main uses of energy resources include:
- Transport
- Electricity generation
- Heating
What are the 8 different energy resources?
- Fossil Fuels
- Nuclear
- Bio-Fuels
- Wind
- Hydroelectric
- Tidal
- Geothermal
- Solar
Enviromental Issues with Energy
- The current evidence for climate change is overwhelming – in order to limit global warming, carbon emissions must be limited globally
- Doing so, however, requires a balanced approach – carbon-neutral energy resources either lack public support, reliability or cannot produce sufficient energy to meet the demand
- Nevertheless, over the past 20 years, there has been a gradual shift towards cleaner technologies
- Government grants have encouraged the development of wind and solar farms
- Coal has gradually been replaced with cleaner natural gas
- A new generation of nuclear power stations are currently in development – although with old power stations being shut down, nuclear power is becoming a smaller option
- Further reduction of carbon emissions will require some further measures:
- More nuclear power stations will be needed to replace existing fossil fuel stations
- A means of storing energy from unreliable sources (such as solar and wind) will need to be developed
- Although science can identify environmental issues arising from the use of energy sources, political, social, ethical and economic considerations must be taken to deal with these issues
- In the past 30 years in the UK:
- Fossil fuel use has dropped from 75% to 38%
- Renewable energy use has increased from 2% to 35%
- Coal used to be the main provider of energy in the UK, but now it is natural gas
- This is because, out of the 3 main fossil fuels, coal produces the most carbon dioxide, while natural gas produces the least
- Switching to gas is not the solution to reducing carbon emissions, but as the use of carbon-neutral energy resources increases, it is a step in the right direction
What is the Greenhouse Gases?
- Global warming is a problem caused by the Greenhouse Effect
- The Greenhouse Effect is caused by the increased concentration and effect of greenhouse gases, mainly methane and carbon dioxide
- The process of global warming is as follows:
- The Sun emits rays that enter the Earth’s atmosphere
- The heat is emitted back from the Earth’s surface
- Some heat is reflected back out into Space
- Some heat is absorbed by Greenhouse gases and becomes trapped within the Earth’s atmosphere, causing the Earth’s average temperature to rise as a result
- The higher the concentration of greenhouse gases, the higher the Earth’s average temperature will rise
