Year 9 ELECTRICITY

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Year 9 ELECTRICITY

• The Kinetic energy of Electrons

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Why is electricity such a useful energy?

• It is easily produced (batteries, generators)
• It is easily and quickly transported
• 107 m/s
• It is easily transformed into useful energy
• Light
• Sound
• Heat
• motion

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How is electricity made?

• Static Electricity was the first method of making
  electricity by touching.
• Electrochemical cells or batteries can also
  produce electric current when the terminals are
  connected.
• Electromagnetic generators produce electricity by
  turning large coils inside a magnetic field.

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Electrostatics

• Electrostatics is about "charge," and about the
  attract/repel forces which electric charge
  creates.
• "Static" electricity appears whenever two
  different insulating materials are in contact and
  then separated again.
• All that's required is the touching. Chemical
  bonds are formed when the surfaces touch, and if
  the atoms in one surface tend to hold electrons
  more tightly, that surface will tend to steal
  charged particles from the other surface
  immediately as they touch.
• One surface now has more electrons than protons,
  while the other has more protons than electrons.
• When the surfaces are later separated, the
  objects are now oppositely charged
• Good site http//amasci.com/emotor/stmiscon.html
  five

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How sparks are produced

• Charged objects try to lose their charge and be
  neutral.
• This happens when the object is touched or
  earthed.
• When the charge is really large such as a storm
  cloud or a spark plug if the gap is small enough,
  air will conduct the charge and a spark
  (lightning bolt) is made.

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Electric Fields

• An electric field is a force field.
• It works like gravity except that the objects in
  the field must be charged to attract or repel.
• The field can be around an object that is
  charged.
• He field can also be restricted to a path as it
  is in electric currents

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How do electric currents move?
electrons
Battery
wire
coil
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What do you need for an electric circuit?

• Battery (push electrons)
• Connected wire (transport electrons)
• Load or resistance (use up electrons energy)

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Typical Circuit
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Important Terms in a circuit

• Voltage
• energy supplied by battery
• - energy used by load

9V
1.5V
12V
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How Batteries work

• Car batteries are wet cells, torch batteries are
  dry cells
• Consist of cells (each dry cell is 1.5 Volts)
• A cell contains 2 electrodes and a liquid in
  between (or a paste for a dry cell)
• Chemical reactions inside make their electrodes
  charged so they pull electrons from the negative
  terminal to the positive.

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Battery Life
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Current

• Amount of electrons flowing through a circuit.
• Same all the way around a single path
• Measured in amps
• Large currents Kill

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Circuits

• Loops must be closed (Switches closed, all wires
  connected.
• The loop must go once through everything.
• Current cant go two different ways in a circuit.

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Series Circuits

• These have all the components connected one after
  the other ( to -, to etc.)
• If one component doesnt work they all dont
  work.
• The more components you add the less energy
  (voltage ) is available for each one.

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Parallel Circuits

• These have more than one path the electrons can
  take.
• If one component doesnt work, the others will
  still work.
• The more components you add the same energy is
  used by each component.
• The battery goes flat quick and more amps are
  generated.

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Would you use series or parallel?

• To connect a switch and a lamp?
• To connect lights in a house?
• To connect christmas lights?
• To connect many batteries in a torch?
• To connect a dimmer switch?

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When is the Light on?
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Resistance

• Measures how much a load reduces current.
• High resistance produces low current and a lot of
  heat
• Measured in Ohms ?

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Resistors

• All electrical components added to a circuit have
  some resistance (and lower the current) e.g.
  lamps, speakers, buzzers.
• Special components called resistors are used
  purposely to lower the current and the voltage
  for other electrical components
• The size of a resistor is shown by the coloured
  rings.

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Electronic Systems

• These are specialised circuits where it is not
  just used to produce energy but for control
• Control occurs when the circuit can process the
  current signals coming in and decide what type of
  signals to give out.
• These circuits always have an Input, Processor
  and Output (as well as a power supply)

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e.g. Burglar Alarm

• Input Light dependant resistor
• to trigger a change in light
• (from an intruders shadow)
• Processor Transistor or Integrated
• circuit to turn the alarm on or off.
• Speaker or buzzer- to sound the alarm

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Input Components- also called SensorsDevices
that vary their resistance when conditions change

• switch on no resistance, off infinite
  resistance
• light dependant resistor light level changes
  resistance
• Infrared receiver infrared light level changes
  resistance
• thermistor temperature changes resistance
• microphonesound level changes resistance

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Output Components-Electrical Energy Convertors

• Light bulb
• speaker or buzzer
• motor
• Light emitting diode.

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Processors

• Processors are the control part of the circuit
  since they actively decide what signal to pass on
  from the input to the output
• Many electronic components are
• available to change the input electric
• current into other types of current
• e.g. AC to DC, analogue to digital
• high voltage to low voltage etc.
• Examples
• Transistors (amplify current)
• Capacitors (stores current, then releases it for
  a certain time)
• other Integrated circuits or microchips that are
  used for specific purposes.