Chapter 13 Electricity

1
Chapter 13 Electricity
2
Physical ScienceChapter 13 Section 1

• Objectives
• Indicate which pairs of charges will repel ad
  which will attract.
• Explain what factors affect the strength of the
  electric force.
• Describe the characteristics of the electric
  field due to a charge.

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Electric Charge

• Electrical property of matter that creates a
  force btwn objects
• Opposite charges attract
• Charges are or
• If amount of and charges are equal, there is
  no net charge (0)

4
Electric Charge

• Proton
• Electron
• Neutron 0
• Both protons and e- have a charge value of 1.6 x
  10-19 C
• Object has a charge when the of protons and e-
  are unequal
• This difference determines the charge
• More protons charge
• More electrons - charge
• SI unit of charge is the coulomb (C)

5
Demo.

• Balloons and charge

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Conductors

• Allow charge to flow
• ex. metals

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Insulators

• Do not transfer charge easily
• ex. cardboard, glass, silk, plastic

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Transfer of Charge

• Objects can be charged by a transfer of e-
• Outer e- move from one object to another
• Can happen by rubbing two objects together
• Charging by friction
• Can happen by touching a neutral object w/a
  charged one
• Charging by contact

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Demo.

• Charging by friction and induction

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Polarization

• One side of object is more and the other side
  is more
• Charges move w/in uncharged objects
• If you hold a charged object near a neutral
  object it will pull the oppositely charged
  particles to it

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Demo.

• balloons

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Electric Force

• Force of attraction or repulsion btwn objects due
  to charge
• ex. static cling
• What holds atoms together
• Helps in bonding
• d/o amount of charge and the distance btwn
  objects
• Is there even if objects do not touch

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Electric Field

• Region around a charged object in which other
  charged particles experience an electric force
• Charged particles produce an electric field
• Shown w/electric field lines
• point outward
• - point inward
• Lines never cross
• Lines show strength
• More lines more strength

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Review and Assignment

• Indicate which pairs of charges will repel ad
  which will attract.
• Explain what factors affect the strength of the
  electric force.
• Describe the characteristics of the electric
  field due to a charge.
• Assignment WS

15
Physical ScienceChapter 13 Section 2

• Objectives
• Describe how batteries are sources of voltage.
• Explain how a potential difference produces a
  current in a conductor.
• Define resistance.
• Calculate the resistance, current, or voltage,
  given the other two quantities.

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Electrical PE

• Electric charge has PE
• PE of a charged object is due to its position in
  an electric field
• Decreases as distance btwn alike charges
  increases
• Increases as distance btwn opposite charges
  increases

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Potential Difference

• Change in the electrical PE divided by charge
• Occurs as a charge moves from one place to
  another in an electric field
• Unit is volt (V) 1 J/C
• Also called voltage

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Batteries

• Use potential difference
• Voltage in batteries ranges from 1.5 V to 12 V
• Most batteries are an electric cell
• Convert chemical E to electrical E
• One terminal is and the other is
• Contain an electrolyte and 2 electrodes
• Can be a wet or dry cell
• When switched on, e- move from to terminal

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Batteries

• When charges are moved by an electric field to a
  lower PE, a current is produced

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Current

• Rate that electric charges move through a
  conductor
• Unit is ampere (A) 1 C/s
• Can be or or both
• Direction is opposite the direction of e-
  movement

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Direct Current

• Batteries
• Charge always travel from negative terminal to
  the terminal in the same direction
• Conventional current movement of charge

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Electrical Resistance

• Ratio of voltage to current

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Example

• 40 W bulb vs. 100 W bulb
• Resistance is caused by internal friction that
  slows movement of charges
• 40 W bulb has more resistance, so it is dimmer
• Causes bulb to be warm b/o friction

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Resistance

• Resistance voltage/current
• R V/I V IR I V/R
• Unit is the ohm (O) or V/A
• Resistor conductor that controls current

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Review and Assignment

• Describe how batteries are sources of voltage.
• Explain how a potential difference produces a
  current in a conductor.
• Define resistance.
• Calculate the resistance, current, or voltage,
  given the other two quantities.
• Assignment WS

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Physical ScienceChapter 13 Section 2 day 2

• Objectives
• Distinguish between conductors, superconductors,
  semiconductors, and insulators.

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Conductors

• Have low resistance
• Movement of charges d/o how tightly e- are bonded
  together
• Conductors allow e- to flow easily
• ex. Cu, alloys, C
• Some substances have 0 resistance when their
  temperature drops below a certain temperature
  (superconductors)

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Insulators

• Have high resistance
• Prevent electric current from leaking
• ex. plastic coating

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Semiconductors

• Have properties btwn conductors and insulators
• Used in computers and electronics

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Inquiry Lab

• p. 144

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Review and Assignment

• Distinguish between conductors, superconductors,
  semiconductors, and insulators.
• Assignment

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Physical ScienceChapter 13 Section 3

• Objectives
• Use schematic diagrams to represent circuits.
• Distinguish between series and parallel circuits.
• Calculate electric power using voltage and
  current.
• Explain how fuses and circuit breakers are used
  to prevent circuit overload.

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Circuits

• Path through which charges can move or be
  conducted
• Battery, wire, bulb, switch
• E- move from terminal to one

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Closed Circuit

• Closed loop path
• Current can flow

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Open Circuit

• Open loop path
• Current cannot flow

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Switch

• Helps open and close circuits

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Schematic Diagrams

• Show an electric circuit w/graphics
• Resistor
• Bulb
• Battery
• Open switch

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Series Circuit

• Has a single path for current
• Charges cannot build up
• Current in each device is the same
• If an element is removed the circuit will not work

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Parallel Circuit

• Has multiple paths for current to travel
• Voltage across each device is the same
• A break in the path does not interupt current flow

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Demo.

• circuits

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Electrical Energy

• Needed to run electrical devices
• Comes from a battery or a power plant
• Electric power is the rate at which electrical E
  is used
• When charges move they lose E
• E is turned into work
• P IV I P/V V P/I
• Unit is Watt (W)

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Circuit Overload

• Circuits can be overloaded w/too much current
• Short circuit
• Can be prevented w/fuses and circuit breakers
• Fuses melt and open circuit
• Circuit breakers open to open circuit

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Review and Assignment

• Use schematic diagrams to represent circuits.
• Distinguish between series and parallel circuits.
• Calculate electric power using voltage and
  current.
• Explain how fuses and circuit breakers are used
  to prevent circuit overload.
• Assignment WS