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Magnetism

Magnetism. What is the relationship between magnetism and electricity?. Jack T. Duncan Physical Science. EQ1: What is magnetism?. Magnetism – the properties and interactions of magnets 1. All magnets have magnetic forces – ability to attract or repel.

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Magnetism

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  1. Magnetism What is the relationship between magnetism and electricity? Jack T. Duncan Physical Science

  2. EQ1: What is magnetism? • Magnetism – the properties and interactions of magnets 1. All magnets have magnetic forces – ability to attract or repel. 2. The magnetic field surrounds a magnet and exerts magnetic lines of force. - stronger when closer to magnet

  3. EQ2: How do magnets behave? • Magnetic poles – regions of magnet where the magnetic forces are the strongest - magnetic lines are the most numerous 1. All magnets have a north(N) and south(S) pole. - Two unlike poles (N-S) – attract - Two like poles (N-N & S-S) – repel * make drawings

  4. Earth’s magnetic poles 2. The earth has north and south magnetic poles. - different locations than the earth’s geographic poles ( N magnetic pole – Canada) - the compass – is a freely rotating magnetic needle that responds to the earth’s magnetic poles by pointing North. - Lodestone (magnetite) – a natural magnet was used as the first compass on ships.

  5. Magnetic materials 3.Magnets (natural and man-made) are usually made up of ferromagnetic materials such as iron, nickel, cobalt and steel. - only strongly attracted to these ferromagnetic materials; has little or no attraction for other types of materials.

  6. Magnetic domains 4. Magnetic domains – groups of atoms that behave like tiny magnets. - If magnetized – domains line up in same direction - If un-magnetized – domains remain in a random arrangement * make drawings

  7. Unmagnetized Material Magnetized Material

  8. Permanent magnets • Permanent magnets – made by placing magnetic materials in a strong magnetic field causing a magnetic domains to line up. - most are made of iron/steel and a combination of other elements - Ex. Alnico – very strong permanent magnet - magnetism can be destroyed by heating, striking the magnet, and over long time periods

  9. Temporary magnets • Temporary magnets – are made up of magnetic materials but do not last a long time - by making contact with a magnet - by stroking the material in same direction with a permanent magnet - by using electricity (electromagnet)

  10. EQ3: What is electromagnetism and why is it so important? • Electromagnetism – the force created by the relationship and interaction between electricity and magnetism. • Contributions by two important scientists: 1. Hans Christen Oersted - 1820 - a Danish physicist who discovered that an electric field in his experiment set up a magnetic field and affected a nearby compass.

  11. Electromagnetism 2. Andre Marie Ampere – 1821 - a French physicist who discovered that coils or loops of conducting wire carrying current produces an even stronger magnetic field. - the more coils or loops, the stronger the magnetic field

  12. Electromagnetism • In 1825, scientists discovered the first electromagnet. • Electromagnet – a temporary magnet produced with a soft iron core material surrounded by coils or loops of wire(solenoid) that is controlled by electricity. - ways to increase the strength: 1) increase coils 2) increase current & 3) larger iron cores

  13. Uses of electromagnets • Many common and important uses of electromagnets: 1.Telephones 2. Doorbells 3. Stereo speakers 4. Pick up scrap metal (using a crane) 5. Electric motor*

  14. EQ5: How does the electric motor work? • Electric motor – a device that changes electrical energy into mechanical energy 1. The electromagnet is free to rotate between the poles of a permanent fixed magnet. 2. Electric current flowing around the coils of an electromagnet sets up a magnetic field. 3. Changing direction of current causes the poles to constantly reverse and rotate.

  15. Electric motors 4. The rotating electromagnet is connected to a shaft that turns parts or gears for motion. • Electric motors are found in many appliances and tools that have moving parts: Ex. Fans, mixers, washing machines, drills, saws, toys etc.

  16. EQ6. What is electromagnetic induction and why is it so important? • Electromagnetic induction (induced current) - the production of an electric current from a magnetic field. Two ways: • Moving a loop or coil of wire through a magnetic field. • Moving a magnet through a loop of wire.

  17. Electromagnetic induction • Contributions by two important scientists; 1. Michael Faraday – 1831 - an English scientist who discovered that an electric current could be caused by moving a wire through a magnetic field. 2. Joseph Henry – an American scientist made a similar discovery

  18. Electromagnetic induction • As a conducting wire cuts through the magnetic lines of force, it induces an electric current (Faraday’s law). • Galvanometer – instrument used to detect and measure very small amounts of electric current • The discovery of electromagnetic induction led to important inventions such as the electric generator and transformers.

  19. EQ7: How does the electric generator work? • Generator – a device that produces electricity from mechanical energy by rotating a coil of wire in a magnetic field. - the coil is rotated by an outside source of mechanical energy. - as the coils rotate within the magnetic field, an electric current flows through the coil.

  20. Generator - The coils of the electromagnets are connected to a turbine – large wheel with blades that rotates when pushed by water, steam or wind. - The direction of the coil changes twice with each revolution – producing alternating current (AC) • At power plants generators produce AC at a rate of 60 cycles/second or 60 Hz – changing direction 120 times/second.

  21. EQ8: How does a transformer work? • Transformer – a device that increases or decreases the voltage of AC. - made of two coils (primary and secondary) wrapped around the same iron core. - changes of current in the primary coil (incoming voltage) induces a change in the current in the secondary coil (outgoing voltage).

  22. Transformer • Two types of transformers: 1. Step-up transformer – the secondary coil has more loops or coils than the primary coil. - it increases the voltage - located at power plants and along the route at power substations to boost it up to travel long distances

  23. Transformer 2. Step-down transformer – the primary coil has more loops or coils than the secondary coil. - it decreases the voltage - located on utility poles (round bucket) and used for certain appliances and toys (trains). - can reduce very high voltage from power lines (750, 000 V) down to household use of 110 – 220 V of AC.

  24. Transformers

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