Electricity

• Cell


  Store of chemical energy

  
• Battery

  Two or more cells

  
• Open switch


  Switches circuit off as the current cannot flow through the break

  
• Closed switch


  Completes the circuit so current can flow through

  
• Fixed resistor

  Affects size of current and cannot be changed

  
• Ammeter


  Measures current

  
• Voltmeter

  Measures potential difference (voltage)

  
• Variable resistor

  Allows the current to vary

  
• Fuse


  A safety device with a thin metal strip that will melt if too much current passes through a circuit; prevents electrification

  
• Diode


  Allows current to only flow in one direction

  
• Light Emitting Diode (LED)

  Emits light when electricity passes through in one direction and prevents electricity from going in the reverse direction

  
• Potential Difference


  - voltage

  - electrical work done by a cell

  - measured in volts
• Current in metals


  - current carried by delocalised electrons

  - electrons are repelled from negative terminal and attracted to the positive terminal
• Current in a circuit

  - current flows from positive to negative
• Unit of charge


  Coulombs (C)
• Unit of current


  Amperes (A)
• Direct current


  Current flows in one direction
• Series circuits

  Current is constant

  (R = R1 + R2)
• Parallel circuits


  - current split between branches

  - same potential difference at each branch
• Alternating current


  Direction continually changes
• Current


  - flow of electrical charge

  - depends on resistance and potential difference
• Potential difference


  - a measure of energy transferred between two points in a circuit (pushes the charge around)
• Resistance


  Anything that limits the flow of the current (measured in ohms Ω)
• Flow of charge is...

  opposite to the flow of electrons
• Electricity practical 6 marker: IV Graphs

  1. set up equipment

  2. use the variable resistor to control the voltage

  3. only switch on to take a reading

  4. measure current and voltage on multimetre

  5. measure a range of voltages increasing by 10v each time

  6. graph voltage and current to find the resistance
• IV Graphs - Resistor

  Current is directly proportional to potential difference

  
• IV Graphs - Filament lamp

  As the current increases, electrons collide with ions in the metal lattice, causing faster vibrations and a rising temperature. This creates a higher resistance

  
• IV Graphs - Diode

  Current will only flow in one direction, so the reverse direction has a high resistance

  - uses: changes AC to DC

  
• Thermistor graph


  - temperature dependent resistor

  - as temperature increases, resistance decreases

  - used in temperature detectors, eg electronic thermostats

  
• Light dependent resistor (LDR) graph

  - light intensity dependent resistor

  - as light intensity increases, resistance decreases

  - used in automatic night lights, outdoor lighting and burglar detectors

  
• Current in a series circuit

  Same across all branches
• Current in a parallel circuit

  Shared across branches
• Voltage in a series circuit

  Shared across branches
• Voltage in a parallel circuit

  Same across all branches
• Brown wire


  - live wire

  - carries 230v potential difference

  - provides alternating voltage
• Blue wire


  - neutral wire

  - at/ close to 0v (earth potential)

  - completes circuit and carries current away from appliance
• Green and yellow wire

  - earth wire

  - safety wire

  - only carries current if fault occurs

  - stops appliance from becoming live
• Alternating Current (AC)


  - changes direction

  - sources: plugs
• Direct current (DC)


  - only flows in one direction

  - sources: batteries/ cells
• Resistance in a series circuit

  - more resistors mean a larger resistance in the whole circuit