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Electricity

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Title: Electricity


1
Electricity
  • Chapter 7

Physical Science
2
Vocabulary for Electricity
  • Static electricity
  • Conductor
  • Insulator
  • Conduction (charging by contact)
  • Induction
  • Electroscope
  • Voltage
  • Circuit
  • Current
  • Dry cell
  • Wet cell
  • Resistance
  • Ohm
  • Series circuit
  • Parallel circuit
  • Circuit breaker

3
Electric Charge
  • All matter is made up of ATOMS
  • An atom is the smallest part of an element that
    has all the properties of that element
  • Atoms are made of smaller particles called
    subatomic particles
  • These particles include protons, neutrons and
    electrons
  • Both protons and electrons have a basic property
    called electric charge

4
Basic structure of an atom
Helium Atom
N
P
P
E-
E-
N
Nucleus of atom Contains protons and neutrons Is
positively charged
Energy level Contains electrons Has a negative
charge
5
Charge and Force
  • Protons are positively charged
  • Electrons are negatively charged
  • Neutrons have no charge
  • Opposite charges attract each other and can cause
    a force of push or pull
  • An atom has no overall charge why?
  • Equal number of protons and electrons causes this
    to be true.
  • Protons cannot move, but electrons can move freely

P
E -
N
6
Electric Fields
  • An electric field is a region surrounding a
    charged particle where other charged particles
    are affected
  • A force of attraction occurs if there is an
    opposite charge.
  • A force of repulsion occurs if there is the same
    charge
  • An electric field is the strongest near a charged
    particle
  • The electric field is weaker when it is far away
  • So the strength of an electric field depends upon
    the distance from the charged particle

7
Static Electricity
  • The word static, means not moving or stationary
  • Static electricity is a build up of electric
    charges on an object
  • The three ways electric charges can build are,
    friction, conduction, and induction
  • Friction Electrons are held loosely so rubbing
    a balloon against a cloth will transfer the
    electrons to the balloon.
  • Conduction Direct contact is required for
    electrons to move through a conductor
  • Induction No contact is necessary.
    Rearrangement occurs as repulsion and attraction
    work together to cause a charge

8
Continued
  • A great example of a dramatic natural static
    electrical discharge is lightning.
  • An electroscope is an instrument that detects a
    static charge.
  • Static charges like to return to the ground and
    try to balance themselves. (grounding)
  • We use grounding rods called lightning rods on
    our homes to protect them from lightning. Ben
    Franklin invented these devices for us.
  • There are six types of lightning. Heat, sheet,
    fork, bead, ribbon, and ball.
  • Rapid expansion of the air from the heat of the
    spark is what causes the thunder we hear.
  • Lightning can travel from ground to cloud, cloud
    to cloud, or cloud to ground.

9
Lightning Facts
  • Conditions needed for lightning to flourish are
    warmth and humidity.
  • Around the world there are 100 lightning strikes
    every second.
  • Weather meteorologists use an instrument called
    an interferometer to track electrical fields.
  • An average of 3 people per year are struck by
    lightning while talking on the telephone.
  • A lightning bolt is about an inch in diameter.
  • 4 out of 5 people struck by lightning will
    survive.
  • Lightning will always take the path of least
    resistance.

10
Voltage
  • The measure of energy that is used to move
    electrons is called voltage.
  • Voltage is also known as potential difference.
  • Voltage is the push that makes electrons move.
  • The higher the voltage, the more energy the
    electrons carry. More voltage more energy.
  • The more energy each electron has, the more work
    can be done.
  • The unit used for measuring voltage is the
    volt.
  • A voltmeter is used to measure voltage.
  • The letter V, is used to represent voltage.

11
The Flow of Electricity
  • The flow of electrons through a wire is called
    electric current.
  • Current is measured by how many electrons pass a
    given point in one second.
  • High current more electrons.
  • The symbol for current is the letter I.
  • The unit used to measure current is the ampere
    (A).
  • Ammeters and galvanometers are used to measure
    current.
  • One amp is the amount of current that flows past
    a given point in one second.

12
Resistance
  • Resistance - The opposition to the flow of
    electricity.
  • Symbol for resistance is the letter R.
  • The unit for resistance is the Ohm.
  • Some materials conduct better than other
    materials.
  • Poor conductors will have a high resistance to
    the flow of electricity.
  • Some materials are nonconductors and are used as
    insulators.
  • Resistance is also affected by a wires thickness,
    length and temperature. How?

13
Resistance continued.
  • Longer wire more resistance
  • Thinner wire more resistance
  • Can you think of a reason resistance might be
    good to use?
  • While slowing down the flow of electrons, heat
    and energy are released, sometimes used for
    heating elements or filaments in light bulbs.
  • Super conductors often need extremely cold
    temperatures to work efficiently.

14
Ohms Law(law of electrical resistance)
  • Ohms law states that the current in a wire is
    equal to the voltage divided by the resistance.
  • Current voltage/resistance
  • IV/R
  • What would happen if the resistance increases and
    the voltage stays the same?
  • What would happen if the resistance decreases and
    the voltage stays the same?
  • What must happen to the resistance if the voltage
    increases and the current stays the same?

15
Producing a Current
  • We must have a source of electrons to produce a
    current
  • Electrochemical cells provide a steady supply of
    electric current from a chemical reaction
    occurring in the cell.
  • Dry Cells Are not really dry, but contain a
    paste that reacts with the zinc container.
    Electrons then travel to the carbon rod in the
    center for our use.
  • Electrons flow from the negative terminal to the
    positive terminal of a battery.
  • Negative charges build up on the negative
    terminal and then flow through the machine to
    reach the positive terminal of the battery.

16
Producing current continued.
  • Wet Cells (also called voltaic cell) Metal
    plates called electrodes,(copper and zinc), are
    placed in an electrolyte, usually a type of acid.
  • The chemical reaction between the electrodes and
    the acid causes electrons to pile up on the zinc
    electrode which is negatively charged.
  • Electron pressure pushes the electrons from the
    zinc plate to the copper plate which is
    positively charged.
  • The wire connecting the two electrodes gives us
    the pathway for a steady flow of electric current.

17
Thermocouples
  • Thermocouple is a device that changes heat energy
    into electrical energy.
  • If the ends of a piece of copper wire and iron
    wire are joined and one of the connections is
    heated while the other is cooled, we will be able
    to produce a current.
  • The greater the difference in temperature, the
    greater the current.
  • Thermocouples are used in cars, ovens, and gas
    furnaces.

18
Current Direction
  • Electrons moving through a wire can move in the
    same direction or they can travel back and forth.
  • Direct Current (DC) Electrons always flow in
    one direction negative to positive.
  • Alternating Current (AC) Electrons reverse
    their direction regularly.
  • The current in your home is AC and changes
    direction about 60 times per second or 60 cycles
    per second.

19
Electric Circuits
  • In order to flow, electrons need a closed path
    through which to travel.
  • An electric circuit provides a complete, closed
    path for an electric current.
  • Parts of a circuit include, load or resistance,
    wires and a switch.
  • Load The device that uses the electric energy.
    Usually offers some resistance to the flow.
  • Switch Opens and closes the circuit.
    Electricity cannot flow through an open circuit.

20
Circuits
(Simple series)
Switch
Battery
-

Load or resistance
21
Parallel Circuit
-

The different parts of a parallel circuit are on
separate branches. Therefore, each can work
independent of the other.
22
Electric Power
  • Power The rate at which work is done or energy
    is used.
  • Electric power The measure of the rate at which
    electricity does work or provides energy.
  • Power Voltage x Current or PV x I
  • Also can be written
    Watts Volts x Amperes
  • According to this formula, one watt of power is
    delivered when a current of one ampere flows
    through a circuit whose voltage is one.

23
Electric Energy
  • The formula for electric energy is
    energy power x time, or, E
    P x t
  • The unit for energy from electricity is kilowatt
    hours.
  • Large quantities of power must be measure in
    kilowatts or units of 1000 watts.
  • So, kilowatts times hours kilowatt hours

24
Electrical Safety
  • Fuses are designed to protect your circuits by
    burning out if too much current is flowing at
    once.
  • Circuit Breaker Takes the place of a fuse by
    turning off the power if too much current runs
    through them at once.
  • Fuses must be replaced, but circuit breakers can
    be reset.
  • Respect electricity because it will always take
    the easiest path to ground, which could be
    through your body.

25
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26
Circuits
27
Series Circuit
28
Parallel Circuit
29
Ohms (resistance)
30
Ohms circle
31
Will these Circuits Work? 1) Look at each circuit
diagram below.2) Do you think the bulb(s) will
light? If you do, put a tick in BOX A under the
diagram. If not, put a cross.3) Now make the
circuit using the equipment. Does the bulb light?
If it does, put a tick in BOX B. If not, put a
cross.4) Repeat this for all of the circuit
diagrams. Then compare your predictions (BOX A)
to your results (BOX B).
Created by Mark Warner - Teaching Ideas for
Primary Teachers - http//www.teachingideas.co.uk

32
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