Energy

• stores of energy: Magnetic, Thermal, Chemical, Kinetic, Electrostatic, Elastic potential, Gravitational potential. Nuclear
• Nuclear energy: the energy stores inside of a nucleus.
• Electricity through the kettle increases the internal energy of the element which in turn increases the internal (thermal) energy of the water which increases the temperature of the water
• • mechanical work - a force moving an object through a distance
  • electrical work - charges moving due to a potential difference
  • heating - due to temperature difference caused electrically or by chemical reaction
  • radiation - energy transferred as a wave, eg light and infrared - light radiation and infrared radiation are emitted from the sun
• Doing 'work' is the scientific way of saying that energy has been transferred.
• 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.
• No system is perfect. Whenever there is a change in a system, energy is transferred and some of that energy is dissipated. (The spreading out and transfer of energy stores into less useful forms, such as thermal energy causing the surroundings to heat up. Dissipated energy is often referred to as 'wasted' energy, since it is not transferred to a useful output.)
• 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.
• Examples of dissipation

  Energy is usually lost by heating up the surroundings though sometimes energy is dissipated as sound waves.
• The conservation of energy

  Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed.
• The skydiver

  When a skydiver jumps out of a plane, he begins to lose gravitational potential energy as his height decreases and he gains kinetic energy as his speed increases.
• The light that comes from a smartphone is emitted as light radiation, and the sound waves are produced by a speaker that vibrates back and forth
• kinetic energy: 0.5 * mass * speed^2
• elastic potential energy: 0.5 * spring constant * extension^2
• gravitational potential energy: mass * gravitational field strength * height
• energy transferred = work done

  Energy transferred and work done are both measured in joules (J).
• work done = force × distance
• power: work done / time
• efficiency = useful energy transferred / total energy transferred
• percentage of efficiency: efficiency * 100
• Energy transfer

  As well as transferring energy from one store to another, energy is transferred or transmitted from place to place. As it moves through a substance, energy is transmitted by conduction, convection or radiation.
• All metals are good conductors. When one end of a metal rod is put into a fire, the energy from the flame makes the ions in the rod vibrate faster. Since the ions in the solid metal are close together, this increased vibration means that they collide with neighbouring ions more frequently. Energy is passed on through the metal by these collisions, transmitting the energy. More frequent collisions increase the rate of transfer.
• Comparing conductivities

  The conductivity of materials can be compared by examining the time taken to transmit energy through them. A fan of rods made of different materials can be heated at one end with the same flame. Whichever rod gets hottest first at the other end is the best conductor. The material that heats the quickest is said to have a high thermal conductivity
• There are different ways to investigate methods of insulation. In this practical activity, it is important to:

  • make and record measurements of temperature and time accurately
  • measure and observe the effect of different materials as thermal insulators
  • use appropriate apparatus and methods to measure the effectiveness of different materials as thermal insulators
• Method for insulation for materials.

  1. Place a small beaker into a larger beaker.
  2. Fill the small beaker with hot water from a kettle.
  3. Put a piece of cardboard over the beakers as a lid. The lid should have a hole suitable for a thermometer.
  4. Place a thermometer into the smaller beaker through the hole.
  5. Record the temperature of the water in the small beaker and start the stopwatch.
  6. Record the temperature of the water every 2 minutes for 20 minutes.
• thickness of insulation

  Wrap a sheet of newspaper around a 100 ml beaker.

  1. Fill the beaker with hot water from a kettle.
  2. Put a piece of cardboard over the beaker as a lid. The lid should have a hole suitable for a thermometer.
  3. Place a thermometer into the beaker through the hole.
  4. Record the temperature of the water in the beaker and start the stopwatch.
  5. Record the temperature of the water every 2 minutes for 20 minutes.
• Different materials require different amounts of energy to change temperature. The amount of energy needed depends on:

  • the mass of the material
  • the substance of the material (specific heat capacity)
  • the desired temperature change
• The specific heat capacity of water is 4,200 Joules per kilogram per degree Celsius (J/kg°C). This means that it takes 4,200 J to raise the temperature of 1 kg of water by 1°C
• change in thermal energy = mass × specific heat capacity × temperature change
• There are different ways to investigate methods of insulation. In this practical activity, it is important to:

  • make and record potential difference, current and time accurately
  • measure and observe the change in temperature and energy transferred
  • use appropriate apparatus and methods to measure the specific heat capacity of a sample of material
• Method for testing heat capacity of a sample material

  1. Place the immersion heater into the central hole at the top of the block.
  2. Place the thermometer into the smaller hole and put a couple of drops of oil into the hole to make sure the thermometer is surrounded by hot material.
  3. Fully insulate the block by wrapping it loosely with cotton wool.
  4. Record the temperature of the block.
  5. Connect the heater to the power supply and turn it off after ten minutes.
  6. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.
• energy transferred = potential difference × current × time
• Systems that can store large amounts of energy are called energy resources. The major energy resources available to produce electricity are fossil fuels, nuclear fuel, bio-fuel, wind, hydroelectricity, geothermal, tidal, water waves and the Sun. Ultimately, all the energy on Earth originally comes from the Sun but has been stored as different energy resources.
• Demand for energy varies with the time of year and the time of day. During early evening a lot of energy is needed for heating, lighting and cooking but overnight there is very little needed while people sleep. During winter there is more heating and lighting required than in summertime.
• Most of the electricity generated globally is still produced by fossil fuels. This is partly due to:

  • the high power output fossil fuels give compared to other energy resources, like wind and water waves
  • the existing infrastructure for extracting, transporting and processing fossil fuels - this makes fossil fuels cheaper than setting up new alternatives
• In some developed countries, nuclear power stations are a growing form of electricity generation. Nuclear fuel can release large amounts of energy compared to fossil fuels and does not emit carbon dioxide. However, the radioactive waste that is produced is difficult to store and dispose of.
• Renewable resources are replenished either by:

  • human action, eg trees cut down for bio-fuel are replaced by planting new trees
  • natural processes, eg water let through a dam for hydroelectricity is replaced through the water cycle

  A non-renewable energy resource is one with a finite amount. It will eventually run out when all reserves have been used up.
• Power stations that use fossil fuels or nuclear fuel are very reliable sources of energy. These two types of station provide much of the country’s electricity. They operate almost continuously. When additional power is needed, gas power stations are usually used because they will come on very quickly and start generating electricity almost immediately.
• The fuel for nuclear power stations is relatively cheap, but the power stations themselves are expensive to build. It is also very expensive to dismantle, or decommission, old nuclear power stations at the end of their useful life and the highly radioactive waste needs to be stored for millions of years before the natural activity will reduce to a safe level.
• • Closed System: A system that experiences no net change in its total energy when energy transfers occur within it