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MAGNETISM/ELECTRICITY A VERY ENLIGHTENING UNIT! SHOCKING ISN’T IT? AREN’T YOU ATTRACTED TO THIS TOPIC? • What happened in Magnesia, Turkey 2000 years ago? • Greeks discovered a mineral that attracted things made of iron, they called it magnetite (after the town it was found in) • Magnet: any material that attracts iron or materials containing iron • Magnetic pole: 1 of 2 points, such as the ends of a magnet, that have opposing magnetic qualities • Magnetic force: the force of attraction or repulsion generated by moving or spinning electric charges • Magnetic field: region around a magnet in which magnetic forces can act • Closer the field lines, stronger the magnetic field • Cause of magnetism: in some metals moving electrons around atoms can align to form domains • Examples of metals that can become arranged into domains: iron, nickel, cobalt • So how do you align the domains? • What would happen to the magnetism of each piece of this magnet if you cut it into smaller pieces? • You would create 2 smaller magnets with new smaller alignments and poles • How can you demagnetize a magnet (in other words, how do you mess up the aligned domains)? • Drop it • Put it near a stronger magnet • Heat the magnet (to high temperature) • Types of magnets: • Ferromagnets: magnet made of iron, nickel or cobalt • Electromagnet: magnet made by running an electric current through an iron core • Can you name a very big magnet? • Hint, it has an enormous iron core of charged electrons aligning into domains • Can you name a very big magnet? • Ever see an example of the earth’s polar field? • What happens when your rub your feet across a carpet or drag the blankets across your bed during dry weather? • Electric Charge: all matter is made up of very small particles called protons, neutrons, and electrons • These protons (+) and electrons (-) are charged particles • Law of electric charges: states that like charges repel and opposite charges attract • Electric force: force of attraction or repulsion on a charged particle that is due to an electric field • The closer together the objects, the greater the electric force • The greater the charge the greater the electric force • Electric field: the space around a charged object in which another charged object experiences an electric force • Friction: occurs when electrons are “wiped” from one object to another • ie: rubbing a balloon on hair causes electrons to move from hair to balloon • Electrical conductor: a material in which charges can move freely • ie: copper, aluminum, gold… • Electrical insulator: a material in which charges cannot move freely • ie: plastic, rubber, glass, wood, air… • Static electricity: electric charge at rest; generally produced by friction or induction • Electric discharge: the release of electricity stored in its source • Conservation of charge: when you charge objects, no charges are created or destroyed, just moved • Total # of protons and electrons stays the same • Electroscope: device for detecting electrical charge • http://members.shaw.ca/len92/stat ic.htm • Electromagnetism: the interaction between electricity and magnetism • About all you can do with this is make a compass needle move • Solenoid: a coil of wire with an electric current in it • Electromagnet: a coil that has an iron core and that acts as a magnet when an electric current is in the coil • It is a solenoid with a piece of iron in the center • Electric motor: device that converts electrical energy into mechanical energy • Galvanometer: device with an electromagnet that measures current • Electric current: the rate at which charges pass through a given point • Measured in amperes (usually called amps or written as the symbol A or I) • There are two kinds of current • Alternating current and direct current • Hence: AC/DC • In direct current, the charges always flow in the same direction • In alternating current, the charges continually shift from flowing in one direction to flowing in the reverse direction • Voltage: the potential difference between two points • Really: measure of how much work is needed to move a charge between two points • Measured in volts • Symbol is V • Think of it this way: • Resistance: the opposition presented to the current by a material or device • Expressed in ohms or the symbol • Superconductors: conductors that have zero resistance due to the very cold temperature of a metal • Photocell: a device that converts light energy into electrical energy • Electric power: the rate at which electrical energy is converted into other forms of energy • Power = voltage X current, or P = V x I • The unit for power is the watt • Another common unit of power is the kilowatt (kW) • = to how many watts? • How does the electrical company bill you for the electricity you use each month? • The amount of electrical energy used in a home depends on the power of the electrical devices in the house and the length of time that those devices are on • Electrical energy = power x time • or E = P x t • If 2000 W (2 kW) of power are used for 3 hours then how many kilowatt hours (kWh) are used? • Electric circuit: a complete, closed path through which electric charges flow • All circuits have 3 basic parts • Energy source (battery…) • Wires • Load (light bulb, radio…) • A switch is used to open and close a circuit • They come in different styles: • Draw each example below Open Circuit Circuit Closed • Series: a circuit in which the parts are joined one after another such that the current in each part is the same • Has only 1 pathway for moving charges • Parallel: a circuit in which the parts are joined in branches such that the potential difference across each part is the same • Unlike series, each load does not have the same current • Unlike series, each bulb (or load) works independently of each other