Electricity From Magnetism Ch 18.3 8th

8/9/2019 Electricity From Magnetism Ch 18.3 8th

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Chapter 18 Section 3


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Identify how a n electric field can makean electric current

Explain how electromagnetic inductionis used in a generator

Compare step-up and step-downtransformers


3/23

Oersted found that an electric fieldproduces a magnetic field

Two scientists: Henry & Faraday Discovered that a magnetic field can make

an electric current


4/23

A battery supplied the electric currentto the wire, making an electromagnet

One wire was wrapped around one halfof an iron ring

A 2nd wire was wound around the otherhalf of the iron ring

A galvanometer measured any currentproduced in the 2nd wire by the magneticfield


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Faraday noticed that the instant heconnected the wires to the battery topointer moved.

The pointer moved again when hedisconnected the battery.

As long as the battery wasconnected, the galvanometermeasured no electrical current.


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Faraday realized that the electricalcurrent in the 2nd wire was made onlywhen the magnetic field was

changing

Electromagnetic induction: the

process by which an electric currentis made by changing a magnetic field


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EC is induced when you move a magnetthrough a coil of wire

Greater EC is induced if you move the

magnet fast through the coil

Greater EC is induced if you add moreloops to the wire

Induced EC reverses direction if themagnet is pulled out rather than pushed in


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http://www.hk-phy.org/energy/domestic/cook_phy/images/em_induction.gif


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An electric current is induced onlywhen wire crosses the magnetic fieldlines

Magnetic force can cause electriccharges to move

This occurs only when the wiremoves through the magnetic field

http://www.skoool.co.za/studynotes/science/uploadedImages/Coord12.20_motor_effect.gif


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A device that converts mechanicalenergy to electrical energy

Parts of a simple generator: Coil of wire

Slip rings

Brushes Permanent magnet

https://reader010.{domain}/reader010/html5/0531/5b1009c361b4e/5b1009cbd752a.jpg


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1. Crank is turned, rotating coil crossesmagnetic field lines, EC is induced inthe wire

2. When coil does not cross field lines,no EC is induced

3. As coil continues to rotate, magnetic

field lines are crossed in a differentdirection, EC is induced in oppositedirection


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http://members.shaw.ca/len92/acdc_inside_generator.gif


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EC produced by the generatorchanges direction each time the coilmakes a turn

It is an alternating current

In large generators in power plants,the magnet is turned instead of thecoils


15/23

The energy that generators convertinto electrical energy comes fromdifferent sources:

Nuclear reactionsBurning coal or gas

WindWater


16/23

A device that increases or decreasesthe voltage of alternating current

2 coils of wire wrapped around aniron ring

The changing magnetic field in theiron ring induces a current in thesecondary coil


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http://www.windows2universe.org/physical_science/physics/electricity/images/transformer_diagram_big.gif


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The number of loops in the primary andsecondary coils determines whether itincreases or decreases the voltage

Step-Up: increases voltage & decreasescurrent

Step-Down: decreases voltage &increases current


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http://www.worsleyschool.net/science/files/transformers/stepup.gif


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http://www.worsleyschool.net/science/files/transformers/stepdown.gif


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http://maryland.sierraclub.org/uploads/transmission%20line.bmp


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Name 2 ways a magnet can inducean electric current in a wire

Describe the differences between astep-up transformer and a step-downtransformer

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Electricity From Magnetism Ch 18.3 8th