Circuit Diagram and Components

• You will be expected to know what each component is and how it behaves in a circuit
• • Diagram of circuit symbols

  A) cell

  B) battery of cells

  C) power supply

  D) DC power supply

  E) AC power supply

  F) fixed resistor

  G) variable resistor

  H) tthermistor

  I) light dependent resistor

  J) heater

  K) potential divider

  L) transformer

  M) magnetising coil

  N) switch

  O) earth/ground

  P) junction of conductors

  Q) lamp

  R) motor

  S) generator

  T) ammeter

  U) voltmeter

  V) diode

  W) light emitting diode

  X) fuse

  Y) relay coil

  
• Power supplies

  • Cells, batteries, power supplies and generators all supply current to the circuit
• Resistors

  • Potential dividers, fixed and variable resistors, thermistors and light-dependent resistors (LDRs) are all used to control current
• Meters

  • Ammeters and voltmeters are used to measure the current and potential difference
  • Ammeters are always connected in series whilst voltmeters are always connected in parallel
• Electromagnetic Components

  • Magnetising coils, relays and transformers use electromagnetic effects
  • Relays use a small current in one circuit to switch on a much larger current in another
  • Transformers 'step up' and 'step down' current and potential difference
• Fuses

  • Protect expensive components from current surges and act as a safety measure against fire
• • Symbol for a diode
  • diodes are occasionally drawn with a horizontal line running through the middle of them

  
• Rectification - If a diode is connected to an a.c. (alternating current) power supply, it will only allow a current half of the time
• Rectification

  A) AC

  B) input

  C) output

  
• Dioide - semiconductors

  • rectifier - allows current to flow 1 way
  • arrow on the symbol shows the direction in which conventional current can flow
• Foward biased diode - extremely low resistance

  • current is allowed to flow
  • lamp lights up
  • arrowhead in the symbol points the same way as the conventional current
• Reverse biased diode - has extremely high resistance

  • lamp doesn’t light
  • diode blocks the current - the current is 0A
• Diodes in the house

  • useful for turning AC current into DC current
  • DC suited for items that need a little power available all the time
  • LEDs - light emitting diode
• Diode only allows the current to flow in 1 direction aka rectified alternating current
• What does a cell look like?

  One ling lone and then one short line

  
• What happens to an LDR when light intensity decreases?

  Resistance increases