P4

• Circuit Symbols


  • Switch (open)
  • Cell
  • Battery
  • Diode
  • LED
  • Resistor
  • Variable resistor
  • Bulb
  • Fuse
  • Voltmeter
  • Ammeter
  • Thermistor
  • LDR
• Switch (open)


  Enables current to be switched on or off
• Cell


  Pushes electrons around a complete circuit
• Battery


  Supplies electrical energy, consists of two or more cells
• Diode


  Allows current in one direction only
• LED


  Light emitting diode emits light when a current passes through it in the correct direction
• Resistor


  Limits the current in a circuit
• Variable resistor


  Allows current to be varied
• Bulb


  Emits light as a signal when a current passes through it
• Fuse


  Breaks the circuit if current exceeds a certain amount
• Voltmeter


  Measures potential difference (voltage)
• Ammeter


  Measures electric current
• Thermistor


  Temperature dependent resistor. Has high resistance when temperature is low
• LDR


  A light dependent resistor. Has high resistance when levels of light are low
• Electric current


  Flow of electric charge. Units amperes, A
• Potential difference


  The potential difference (voltage) between two points in an electric circuit is the energy transferred (or the work done) when a coulomb of charge passes between the points. Units volt, V
• Resistance


  Resistance is caused by anything that opposes the flow of electric charge. Units ohm, Ω
• Charge


  Anything charged that is able to move within a circuit. Electrons or ions. Units are coulombs, C
• Series circuit


  A circuit with only one route for charge to take. The different components are connected in a line, end to end
• Parallel circuit


  A circuit with more than one route for charge to take. Each component separately connected to the +ve and -ve terminals
• Electrical current is NOT the flow of electrons, it's the flow of electric charge, and as charge can be positive or negative then naturally current is in the direction of positive charge flow, and in the opposite direction to negative charge flow
• Increasing or decreasing the potential difference of the circuit

  Affects the current
• Plotting current-potential difference results for different wires


  Tells us about the resistance of these wires
• The steeper the line on a current-potential difference graph


  The lower the resistance of the wire
• Factors affecting resistance of a wire


  • Length of wire
  • Thickness of wire
  • Temperature
• As temperature increases


  The metal nuclei begin to vibrate more. The electrons will have more chance of colliding and so resistance increases
• Standard test circuit


  Used to test components and determine the resistance of a component
• Using the standard test circuit


  1. Measure the current through and potential difference across the component

  2. Calculate the resistance

  3. Obtain IV graphs
• The Ammeter must be in series and placed anywhere in the circuit. The voltmeter must be placed in parallel around the component (so that it can compare the energy the charge has before and after passing through the component)

  
• IV Graph types


  • Ohmic conductor (Fixed resistor or wire)
  • Filament Lamp (bulb) non Ohmic conductors
  • Diode or LED
• Ohmic conductor


  Current and potential difference are directly proportional. Resistance is constant
• Filament Lamp (bulb)


  Resistance of a filament lamp is not constant. As temperature increases, resistance increases. Ions within the lamp vibrate more, increasing collisions with electrons
• Diode/LED


  The current through a diode/LED flows in one direction only. The diode has a very high resistance in the reverse direction
• Equations to learn


  • Charge = current x time
  • Potential difference = current x resistance
  • Energy transferred = charge x potential difference
• Charge


  Coulomb (C)
• Current


  Amperes (A)
• Time


  Seconds (s)
• Potential difference


  Volts (V)
• Resistance


  Ohms (Ω)
• Energy


  Joules (J)