Grade Boundaries

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Grade Boundaries

• A 90
• A 80
• B 70
• C 60

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P5 Electric Circuits
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Model of the Atom

• Electrons Negative
• Protons Positive
• Neurons no charge

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Static Electricity

• Materials can only lose or gain Electrons
• Protons dont move
• This will make them positive or negative
• Static Electricity only happens between two
  insulators.
• Conductors direct the charges to the Earth.

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Structure of Metals

• Conductors
• Electrons free to move
• Insulators
• Electrons are not free to move

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Circuit Symbols

• Open Switch
• Closed Switch
• Lamp
• Cell
• Battery
• Voltmeter
• Resistor
• Ammeter
• Variable resistor
• Thermistor
• Light dependent resistor (LDR)

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Resistance

• Moving electrons can collide with atoms of a
  conductor. This is called resistance.
• Resistance makes it harder for the current to
  flow.
• These collisions also make a conductor hot. EG
  this is why a light bulb is hot.

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Thermistors

• Low Temperatures High Resistance
• High Temperatures Low Resistance

Light Dependent Resistors

• Darkness High Resistance
• Light Low Resistance

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• Complete / Incomplete Circuits

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• Ammeter
• Measures Current in Amps.
• Must be connected in series.

• Voltmeter
• Measures Voltage (Potential Difference) in Volts
• Must be connect in parallel

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Series / Parallel Circuits

• Series if lamp breaks, circuit breaks
• Parallel if lamp breaks, the other lamp will
  still work

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Series Circuits

• Atotal A1A2A3
• Vtotal V1V2V3

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Parallel Circuits

• AtotalA1A2A3
• VtotalV1V2V3

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Ohms Law

• The current is directly proportional to the
  voltage.
• IE if you double the voltage, the current will
  also double.

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Resistors in Series and Parallel
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Electromagnetic Induction

• Moving a magnet through a coil of wire produces
  an electric current.
• To increase the voltage you can
• Move the magnet faster
• Use a stronger magnet
• Increase the number of coils

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Electric Generator

• Rotating coil inside a magnet
• The size of the induced voltage can be increased
  by
• Increasing the speed of rotation of the coil
• Increasing the strength of the magnetic field
• Increasing the number of turns on the coil
• Placing an iron core inside the coil
• Generators produce Alternating Current

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AC/DC

• Alternating Current Produced in Generators.
  Current reverses its flow every half turn of the
  magnet.
• Direct Current Produced by a battery. Current
  flows in only one direction.

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Transformers

• Change the Voltage of an AC supply
• Step-Up Transformer Increases Voltage
• Step-Down Transformer Decreases Voltage

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Transformers

• Primary coil connected to AC supply
• Changing current produces a changing Magnetic
  Field
• This induces an AC in the secondary coil

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Transformer Equation

• Secondary Voltage Number of Coils Secondary
• Primary Voltage Number of Coils Primary

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Power
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Energy Transferred

• Energy Transferred Power x Time
• Energy kilowatt-hours
• Power kilowatts (1000 watts)

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Efficiency

• Energy cannot be created or destroyed. It can
  only be transferred from one form to another.
• Most Electrical Energy is wasted in a lightbulb
  as Heat Energy.

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Cost of Electricity

• Cost Number of Units x Cost of One Unit

Efficiency
Efficiency (useful energy/total energy)x100