electricity

• Electricity 


  Means of transfer energy using moving charge
• Current


  Rate of flow of charge (I), measured in amps (A)
• Charge


  Property of a body which experiences a force in an electric field
• Charge


  Measured in coulombs (C)
• Charge


  Current x time (Q = I x t)
• 1 amp is the current that flows when 1 coulomb of charge passes a point in a circuit in 1 second
• Voltage/Potential difference


  Amount of energy, per unit of charge, transferred between 2 points in a circuit (V)
• Voltage


  Measured in volts (V)
• Resistance


  Measure of how difficult it is for current to pass through a component in a circuit
• Voltage


  Current x Resistance (V = I x R)
• The higher the resistance of a component, the harder it is for current to pass through the circuit
• 1 volt is the potential difference when 1 coulomb of charge transfers 1 joule of energy
• Potential difference


  Energy / Charge (V = E/Q)
• Resistance


  Measured in ohms (Ω)
• Power

  Energy transferred each second, measured in watts
• Power


  Current x Potential difference (P = I x V)
• Conductors have low resistance, Insulators have high resistance
• Power


  Current^2 x Resistance (P = I^2 x R)
• Fundamental units


  • Voltage (V, volts)
  • Current (I, amps)
  • Resistance (R, ohms)
  • Power (P, watts)
  • Charge (Q, coulombs)
  • Energy (E, joules)
• Equations


  • V = IR
  • P = IV
  • P = I^2R
  • E = QV
  • E = Pt
• Circuits

  • Series circuit - single pathway, current flows through all components
  • Parallel circuit - multiple pathways, current splits
• Ammeter


  Device used to measure current, measures the same current wherever placed in circuit
• Potential difference in series circuit


  Potential difference supplied = sum of potential differences across components
• Resistance in series


  Total resistance = sum of individual resistors
• Resistor


  Electrical component that restricts flow of charge
• Current in parallel circuit

  Current is inversely proportional to resistance, splits between parallel paths
• Potential difference in parallel circuit

  Potential difference is equal across each parallel component
• Resistance in parallel


  Overall resistance is reduced as current may follow multiple paths
• Circuit components


  • Open switch
  • Closed switch
  • Lamp/bulb
  • Voltmeter
  • Ammeter
  • Resistor
  • Thermistor
  • Variable resistor
  • Diode
  • LED
  • Fuse
  • Cell
  • Battery
• Thermistor


  • Resistance depends on temperature, decreases with increasing temperature
• LDR (Light Dependent Resistor)


  • Resistance depends on light intensity, decreases with increasing light
• Diode


  Allows current to flow in only one direction
• Static electricity


  Charge that builds up due to friction between insulating materials
• Opposite charges attract, like charges repel
• Electric field


  Lines flow away from positive charges and towards negative charges, stronger field closer together
• Uses of static electricity

  • Spray painting
  • Smoke reduction
• Ohm's law


  Current through a resistor is proportional to potential difference (at constant temperature)
• Fixed resistor


  • Ohmic conductor, follows Ohm's law
• Filament bulb


  • Non-ohmic, resistance increases rapidly as it heats up
• Diode


  • Non-ohmic, resistance decreases rapidly when forward biased