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Mr Palmer's AQA GCSE Physics Notes

	Energy The 9 Forms of Energy Energy cannot be created or destroyed. It only changes from one form to another. The nine forms of energy are: Kinetic Energy: The energy an object has because of its motion. Gravitational Potential Energy: The energy an object has because of its height above the ground. Sound: The energy of pressure wave moving through the air. Heat: The energy of the vibrating particles in an object. Light: Energy in the form of electromagnetic radiation. Elastic Potential Energy: The energy stored in tension or compression, for example a compressed spring or stretched rubber band. Chemical Potential Energy: The energy that can be converted to other forms by chemical reactions. Nuclear Energy: The energy that comes from the breaking apart or combining of atomic nuclei Electrical Energy: The energy of charged particles in motion. When energy changes from one form to another, some of the energy is always lost to unwanted forms of energy. This is usually in the form of heat. For example, light bulbs are designed to light a room, but only about 15 percent of the electrical energy that goes into the light bulb changes into light, the other 85 percent is wasted in the form of heat. According to the laws of physics, it is impossible to design a machine that is 100 percent efficient in changing energy from one form to another. Efficiency Whenever energy is used to perform some task, some of that energy is wasted no matter how well the machine is designed. In nearly all processes, the main loss of energy is due to heat. A machine is said to be highly efficient if it converts a high portion of the energy supplied to it into a useful form. Example: Every second an incandescent light bulb gives off 9J of light energy and 91J of heat energy. What is the efficiency of the bulb? First, determine what is the useful energy. Light bulbs are used for lighting, not heating, so the 91J of heat is the wasted energy and the 9J of light is the useful energy. The total energy is the sum of the two. We can also express this as a percent: Efficiency = 9 percent. ^{Incandescent light bulbs are not very efficient.} Sankey Diagrams ^{A Sankey Diagram showing the energy input and output for a diesel engine.} A diagram that shows how energy is transformed inside a device is called a Sankey Diagram. A Sankey Diagram shows arrows that are in proportion to the size of the energy being used. The wider the arrow, the more energy that is flowing in that direction. Arrows that continue to travel to the right show useful forms of energy. Arrows that diverge downward show the forms of wasted energy. ^{The width of the arrows in a Sankey Diagram is proportional to the amount of energy.} Example: Using the Sankey Diagram, calculate the efficiency of an iPod. ^{Sankey Diagram for an iPod} Total input energy = 13 boxes Useful light energy = 1 box Useful sound energy = 3 boxes Payback Time When choosing which method of insulation to install the home owner should use the most cost effective one. This is determined by the shortest pay back time. Pay back time is calculated by: Example: Which should a home owner install first, a draft stopper that costs £3 and saves £20 a year or double-glazed windows which cost £10,000 and save £5,000 a year? You should install the draft stopper first.	Navigation Physics P1 Topics Heat Energy Electricity Power Electromagnetic Spectrum Nuclear Radiation Origins of the Universe Physics P2 Topics Motion Forces Energy Static Electricity Current Electricity Mains Electricity Momentum Nuclear Physics Other Mathematics for Physics