Electricity and Magnetism

1
Electricity and Magnetism

• Chapter 7 Section 1
• Chapter 8 Sections 2 3

2
Chapter 7 Section 1

• Electric Charge

3
Positive and Negative Charge

• Atoms have particles protons, neutrons, and
  electrons
• p charge no no charge e- - charge
• Same of p and e- atoms are electrically
  neutral

4
Transferring Charge

• Some electrons are bound tighter to some objects
• e- bound to shoe more than carpet
• Shoe gains e- - charged
• Carpet loses e- charged
• Static Electricity accumulation of excess
  electric charge

5
Conservation of Charge

• Def charge can be transferred from object to
  object, but it cannot be created or destroyed.

6
Charges Exert Forces

• Clingy clothes from a dryer
• Opposites attract
• Force depends on distance and size of charge
• Positive clothes like negative clothes
• Like charges repel

7
Electric vs. Gravitational Force

• Electric force from p and e- in H atom is 1039
  times stronger than gravitational force
• Most things gravity force is stronger than
  electrical

8
Conductors and Insulators

• Conductor material where e- move easily
• Metals best conductors copper
• Insulators material where e- do NOT move easily
• Plastics, wood, rubber, glass

9
Charging Objects

• Rubbing materials can transfer e- - one is ()
  the other is (-) ? charging by contact

10
Charge by Induction

• Def rearrangement of electrons on neutral object
  by nearby charged object.

11
Lightning

• Static discharge transfer of charge because of a
  buildup of static electricity
• Clouds have movement of air and rain ? areas of
  and charge build
• Lightning is discharge between cloud and ground

12
Thunder

• Lightning rips e- from atmosphere and produces
  heat increase 25,000oC
• Atoms expand quickly and release sound waves
• Earth is struck 100 times every second

13
Grounding

• Harmful effects from charge build up
• If there is a path to earth relieves build up
• Grounded it will transfer any excess charge to
  earth (big neutral object)

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Electroscope
15
Chapter 8 Section 2

• Electricity and Magnetism

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Basics of Magnets

• Magnetic Field exerts a force other magnetic
  objects
• Magnetic Poles where magnetic force is strongest
• Field goes from North to South

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Earths Magnetic Field
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Compass

• Compass needle is small magnet lines up with
  earths magnetic field
• From north magnetic pole to south magnetic pole

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Electric Current and Magnetism

• Moving electric currents create magnetic field in
  direction of current
• Current increases increase magnetic field

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Electromagnets

• Def temporary magnet made by wrapping a wire
  coil carrying a current around an iron core
• Magnetic field in coil is stronger than straight
  wire
• Solenoid single wire wrapped in cylindrical coil

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Electromagnets

• Solenoid Electromagnet

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Properties of Electromagnets

• Temporary b/c when current stops magnet stops
• Increase strength more turns in solenoid or
  more current
• Useful b/c magnetic strength can be changed
  used for work motors and speakers

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Making Sound

• CD changing musical info ? changing electrical
  current
• Electromagnet is attracted or repelled by
  permanent magnet
• Moves speaker cone to make music

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Rotating Electromagnets

• Reverse current to change poles ? electromagnet
  rotates

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Galvanometers

• Def use electromagnet to measure electric
  current
• Used in gauges in cars

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Electric Motors

• Def device that changes electrical energy to
  mechanical energy

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Simple Electric Motor

• 3 main parts wire coil, permanent magnet and
  battery
• Also have brushes conducting pads connected to
  battery and a commutator split conducting metal
  ring

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Spinning Motor

• Commutator rotates with coil as current runs
  through
• Step 1 Step 2
• brushes not in
  contact with commutator
• Inertia keeps coil spinning

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Spinning Motor

• Step 3 Step 4
• commutator reverses commutator
  current keeps spinning reverses
  current
• again - keeps
• 
  spinning

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Chapter 8 Section 3

• Producing Electric Current

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Mechanical to Electrical Energy

• Moving wire loop through magnetic field ?
  electric current
• Moving magnet through wire loop ? electric
  current
• Electromagnetic induction creating a current by
  changing magnetic field

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Generators

• Def uses electromagnetic induction to transform
  mechanical energy to electrical.
• Move a coil in a permanent magnet

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Switching Current Directions

• Each half-turn poles of coil switch ? current
  switches direction
• Coil keeps rotating current periodically changes
  direction
• US generators rotate 60 times/sec 3,600
  rotations/min

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Using Generators

• This type of generator is used in cars
  alternator
• Lights, accessories, spark plugs
• Running engine turns coil

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Electricity to Your Home

• Huge generators in power plants rotate the
  permanent magnet and the coil stays still
• Electricity is generated in the coil
• A Turbine (large wheel rotates when pushed by
  water, wind or steam) spins the magnet
• Some use thermal energy heat water turn
  turbine (mechanical energy) spin generator
  (electrical energy)
• Pg. 241

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Direct and Alternating Currents

• Current in battery vs. electric generator
• Battery Direct Current (DC) flows in one
  direction through wire
• Wall Outlet Alternating Current (AC) reverses
  direction of current in a regular pattern
• 60 cycles/s 60 Hz ? changes direction 120 times
  each second

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Transmitting Electrical Energy

• Electricity to your house
• Goes through power lines energy ? heat due to
  resistance in wires
• Reduce heat/resistance ? send at high voltage
  150,000 V
• BUT cant use that high of voltage ? goes through
  transformer

38
Transformers

• Def increases or decreases the voltage of an
  alternating current.
• Has primary coil and secondary coil wrapped
  around same iron core
• Current goes in primary coil ? magnetizes core
• As AC current changes direction the poles of
  magnet change
• Changing poles ? creates electric current in
  secondary coil

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Types of Transformers

• Step-Up increases voltage outgoing is higher
• Primary coil smaller than secondary
• Step-Down decreases voltage outgoing is lower
• Primary coil is larger than secondary

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Transmitting AC

• Generator ? step-up tran. ? high voltage lines ?
  step-down tran. ? house