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Magnetism Magnetism is a force exerted by magnets. Magnets are objects surrounded by a magnetic field. A magnetic field is the space around a magnet, in which a magnetic force is exerted. Every spinning electron is a magnet, most atoms’ electrons spin in different directions cancelling their magnetic force. Each magnet has two poles, a north and a south pole. The magnetic poles are one of the regions on a magnet that produces magnetic forces. Like poles will repel each other while opposite poles will attract each other. Electromagnets As an electric current or moving charge passes through a wire it produces a magnetic field. This magnetic field around a wire forms concentric circles. A current-carrying coil of wire with many loops forms an electromagnet. Magnets moved near—or even inside coils of wire induce (cause) a current in the coil. Electromagnets can be used as a motor or generator or simply as a magnet that can be turned on and off. An electric motor is made when a permanent magnet is used to produce a magnetic field in a region where a loop of wire is mounted so that it can turn about an axis. As current passes through the wire, the wire spins as it is repelled and attracted to the magnet. The motor converts electrical energy into mechanical energy. An electric generator is a device that rotates a coil of wire in a stationary magnetic field inducing a voltage in the coil. The generator converts mechanical energy into electrical energy. Law of Conservation of Energy According to the law of conservation of energy, during transformations the total amount of energy stays the same. Energy can be not be created or destroyed; it can only change its form. Energy Conversions Energy can be changed from one form to another. Changes in the form of energy are called energy conversions. Whenever energy is converted, some heat will be released or lost in the process. Forms of energy are: Thermal energy (heat) Light energy Electrical energy Sound energy Kinetic energy (mechanical) Chemical energy Nuclear energy Potential energy All forms of energy can be converted into other forms, examples include: o The sun’s energy through solar cells can be converted directly into electricity. o Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy). o In an electric motor, electrical energy is converted to mechanical energy. o In a battery, chemical energy is converted into electrical energy. o The mechanical energy of a waterfall is converted to electrical energy in a generator. o In an automobile engine, fuel is burned to convert chemical energy into heat energy. The heat energy is then changed into mechanical energy. Energy Flow Diagrams Energy flow diagrams show how energy is transformed as it moves through a system. Accounts for the thermal energy (heat) given off during that transformation. Light bulb Car Engine Microphone Photosynthesis Energy efficiency Useful energy is transferred to where it is required in the form that it is wanted. Other forms of energy are referred to as ‘wasted’ or given off in the form of heat. Strategies to reduce this heat loss are intended to improve the efficiency of a device. Energy efficiency is a measure of how usefully energy is converted by a device. Energy efficient light bulbs are designed to produce more useful light energy for the same amount of input electrical energy by wasting less energy to heat. Use of energy efficient light bulbs is one strategy to conserve or reduce our consumption of energy. Within our homes there are many strategies we can use to conserve energy.