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Chapter 11: Electricity and Magnetism

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Title: Chapter 11: Electricity and Magnetism


1
Chapter 11 Electricity and Magnetism
2
Aim What is electricity?
3
Electricity
  • All matter is made up of atoms
  • atoms are made up of protons, electrons and
    neutrons
  • Protons and electrons can transmit energy in the
    form of electricity
  • When 2 different materials are brought into close
    contract some electrons move to the other
    material
  • Causes the material to become electrically
    charged (positive charge or negative charge)

4
  • Negatively charged-more electrons, less protons
  • Positively charged-more protons, less electrons
  • Static electricity is produced from the buildup
    of positive and negative charges
  • Principles of Electricity
  • Opposite charges attract
  • Like charges repel

5
Aim What is an induced Charge?
6
Induced Charge
  • When a charged balloon is brought near a wall,
    its extra negative charges repel the negative
    charges on the wall
  • The negative charges move to the other side of
    the wall
  • The wall becomes positively charged
  • The balloon has a negative charge causing it to
    be attracted to the wall and stick

7
Aim What are conductors and insulators?
8
  • Conductors
  • Electrons move through a material easily
  • Can cause a spark
  • Ex human tissue touching metal doorknob
  • Insulators
  • Electrons do not flow easily through a material
  • Ex human tissue touching plaster will not cause
    an electric spark

9
Grounding electricity
  • It is dangerous to touch a bare wires
  • Grounding wires of an appliance connects the
    metal case to the ground through the household
    wiring
  • If a dangerous charge builds up the grounding
    wire enables the appliance to share the change
    with the ground
  • Grounding wires protect us from getting dangerous
    shocks

10
Aim How is lightning produced?
11
  • Produced by static electricity
  • Negative charges build up in a cloud
  • The ground has a positive charge
  • When enough negative charges build up they form a
    path to the ground
  • Surge of electric energy heats the air to glow-we
    see lightning
  • Heat makes the air expand rapidly-we hear thunder
  • Lightning has high electric energy, which is
    deadly

12
Aim What is a circuit?
13
Circuit
  • A path along which charged particles can travel
  • Electrons move through the wires and bulbs
  • Consist of a source of electricity, devices and
    connecting wires
  • The source of electricity starts pulling and
    pushing on the electrons and the electrons start
    flowing to the positive end of the source
  • A flow of charged particles moving through a
    circuit is called a current
  • Electrons move from negative to positive

14
Resistors
  • Sources of electricity are rated by voltage
  • As the voltage becomes greater, more negative and
    positive charges can build up at one end
  • Resistor-opposes a flow of electrons
  • It makes the current smaller by opposing the flow
    of electrons
  • The lamp could blow out without the resistor
  • The resistor reduces the current of electrons
    flowing through the lamp to a safe level

15
Short Circuits
  • Short circuit could occur if the current is not
    reduced
  • If the current is not reduced, electrons will
    collide causing the wires to heat up
  • This heat could cause a fire

16
Aim What is the difference between a series
circuit and a parallel circuit?
17
Series Circuit
  • Only one path for the electric current
  • Their voltages are added together
  • Increased crowding of electrons at the negative
    end of one battery
  • Increased removal of electrons at the positive
    end of the other battery
  • Puts more force on electrons in the wires and
    bulbs, which produces more current
  • Light bulbs act as a resistor to prevent a short
    circuit from occurring
  • The flow of charges is the same at any point

18
Parallel Circuit
  • More than one path for current
  • Electricity source makes each path feel the same
    overcrowding of electrons
  • Total current increases when another path is
    added, even though another resistor is present
  • Current in each path depends on the strength of
    its resistor
  • Currents are added together to find the total
    current
  • Total current is the same at any point

19
Aim What is the difference and open circuit and
closed circuit?
20
Open Circuit
  • Incomplete circuit
  • Switch is in the off position
  • There is no current
  • Electrical devices do not receive electric energy
  • Copy circuit 1 in Notebook

21
Closed circuit
  • Complete path for a current
  • Current flows in the wires and devices
  • Current transfers energy to the device
  • Switch is in the on position or closed
  • Copy Circuit 2 in Notebook

22
Aim What is a magnet?
23
Magnets
  • Attract metal objects made of iron, cobalt or
    nickel
  • Attract and repel other magnets
  • Have 2 poles north-seeking pole and a
    south-seeking pole
  • South pole of one magnet repels the south pole of
    another
  • A north magnetic pole attracts a south magnetic
    pole
  • The attraction is strongest at the poles

24
  • Magnetism comes from the motions of electrons in
    atoms
  • Moving electrons cause atoms to line up in the
    same direction
  • Permanent magnets-atoms always stay lined up
  • If brought near and object that is nonmetallic,
    there is no attraction

25
Electromagnets
  • Devices that are made magnetic by an electric
    current
  • Magnetism results from moving electrons in a
    current-carrying wire
  • If brought near a nonmetallic object, there is no
    attraction

26
Aim how is a magnetic Field Produced?
27
Magnetic Field
  • Is the area around a magnet in which other
    magnets can feel attraction or repulsion
  • Magnetic force moves from the north pole to the
    south pole and form closed loops
  • Attraction or repulsion is strongest where the
    arrows are most crowded

28
Earths Magnetic Field
  • Tilt of Earths axis causes the magnetic poles to
    be off true geographic north and south poles
  • Magnetic field is not evenly shaped
  • Compass needle always points to the magnetic
    north pole
  • Earths magnetism is likely caused by electrical
    currents in a fluid metal layer around Earths
    inner core

29
Aim What are the uses of Electromagnets?
30
Electric Motors
  • Used to power toys, elevators, fans, air
    compressors, cranes, some cars and bicycles
  • The spinning force comes from an electromagnet
  • A loop of wire is placed between 2 permanent
    magnets
  • When current passes through the wire, the loop
    becomes an electromagnet

31
Medicine
  • Magnetic resonance imaging (MRI)
  • Strong magnetic field produced by electromagnets
    cause the nuclei in the patients body to behave
    like magnets and line up with the magnetic field
  • This enables radio waves to produce images of
    tissues inside the body

32
Sound
  • Speakers depend on electromagnets to operate
  • Cone in a speaker has an electromagnet
  • Current passes through the electromagnet causing
    the cone to vibrate and produce sound

33
Aim What is the difference between a wet cell
and a dry cell?
34
Wet Cell
  • A device that produces a current in a solution
  • Use chemical reactions to produce an electric
    current
  • Charged particles always move in the same
    direction-direct current
  • Consists of 2 different metal plates in a
    solution
  • Produces a voltage-the difference in the amount
    of potential energy between the plate
  • Voltage is measured in volts

35
  • The amount if current can be measured by an
    ammeter and the unit is ampere or amp

36
Dry Cell
  • Produce an electric current using a moist
    conducting paste
  • Chemical reactions between the paste and the
    plates produce a current
  • Ex battery

37
Aim How does electric current reach your home?
38
Generators
  • Uses mechanical energy to make electricity
  • It produces an alternating current
  • Electric power plants use generators to produce
    electricity for homes and businesses
  • Transformers are used to increase or decrease the
    voltage of the current

39
Power Plants
  • Electric current produced by huge generators
  • Power lines connect the power plants to homes in
    cities and towns
  • Electric current from a generator first passes
    through a transformer that increases the voltage
    anywhere from 120,000 to 500,00 volts
  • Before the current comes into our homes it passes
    through another transformer that decreases the
    voltage

40
  • Household circuits use 120 volts
  • The total current for an entire house is 100 or
    200 amps
  • You can run two appliances on the same circuit,
    which has 20 amps, as long as they do not use
    more amps combined
  • Short circuits occur when too much current flows
    through a wire
  • Fuses and circuit breakers protect homes from
    catching on fire

41
Aim How do you use electrical energy at home?
42
  • Any form of energy can be changed into other
    forms
  • Electrical energy can be changed into 4 other
    types of energy
  • Mechanical Energy
  • Electric energy changes into mechanical when any
    device that uses a motor is used
  • Examples food blenders, electric fans, power
    tools

43
  • Heat
  • Coils get very hot because of an electric current
  • Electrons from the current collide with the atoms
    in the coils
  • Temperature of the coils rise
  • Ex heaters, electric blankets, toasters, hair
    dryer
  • Sound
  • Current causes electromagnets to move a diaphragm
    back forth producing sound waves
  • Ex speakers

44
  • Light
  • 2 types of light bulbs
  • Incandescent
  • Contain a thin metal wire or filament that acts
    like a resistor
  • Electric current heats it causing the filament to
    give off heat and visible light
  • Only 12 of the energy is light
  • Rest of energy is wasted as heat

45
  • Fluorescent
  • Produce more light than heat
  • Series of collisions causes gas inside the glass
    to produce light
  • Fluorescent coating on the outside glows
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