electricity

• cell


  - most common energy source in an electric circuit

  - cells have chemically stored energy

  - energy is given to the electrons which pass through the cell

  - this energy is then passed on to components

  
• battery


  - a combination of two or more cells connected in series

  - the voltage supplied by a battery is the sum of the voltages of each of the cells

  
• lamp


  - converts electrical energy into light energy (and some heat too)

  - an example of an output device

  
• switch


  - used to "break" the circuit

  - creates an open circuit and stops electrons from flowing

  
• resistor


  - has the effect of opposing electrical current

  - the greater the resistance, the lower the current flowing through it

  
• voltmeter


  - used to measure voltage

  - always connected across components (in parallel with them)

  
• ammeter


  - used to measure current

  - always connected in series with components

  
• led (light emitting diode)

  - converts electrical energy into light energy without the production of heat light in a light bulb

  - they only conduct in one direction

  - an LED will need to have a resistor connected in series with it to protect it from being damaged by too large a current flowing through it

  
• motor


  - converts electrical energy into kinetic energy

  - used as an output device

  
• microphone


  - converts sound energy into electrical energy

  - an example of an input device

  
• loudspeaker


  - converts electrical energy into sound energy

  - an example of an output device

  
• fuse


  - safety device

  - contains a piece of wire which melts when the current reaches a certain level

  - appliances usually have a 3A or 13A fuse

  
• diode


  - an electrical one-way-street

  - only allows the current to flow in one direction

  
• capacitor


  - device which stores electrical charge

  - measured in farads, F but more commonly μF

  - whilst a capacitor is charging, the voltage across it increases until it reaches the voltage of the supply

  - can be used to create a time delay in a circuit

  
• thermistor


  - a temperature dependant resistor

  - as temperature, increases resistance

  decreases
• ldr (light dependant resistor)


  as light level increases, resistance decreases
• current

  the quantity of charge passing a point in the conductor per unit of time
• alternating current, a.c.

  current which continuously changes direction, back and forth, usually many times every second
• the mains supply


  - provides an alternating current

  - has a frequency of 50 Hz, which means that the current changes direction 50 times every second

  - its quoted voltage is 230 V, and its peak voltage is 325 V
• oscilloscope


  - measures peak voltage

  - a.c. ~ the current changes direction when the trace (the black line) crosses the midline on the screen

  - d.c. ~ the trace on the screen never crosses the midline
• direct current, d.c.


  current which always flows in the same direction, from negative to positive
• d.c. example


  battery
• electric field


  - a region of space in which a charged particle will experience a force

  - the field lines show the direction in which a positive charge would experience a force in the field

  
• the closer together the field lines, ...

  the stronger the electric field is at that point
• potential difference, p.d.


  - the work done in moving one coulomb of charge/the energy given to each coulomb of charge

  - measured in volts
• series circuit


  the current has only one path it can follow to get from one terminal of the power supply to the other terminal
• parallel circuit


  the current has more than one path it can follow
• voltage in series circuit

  adds up to give the supply voltage
• voltage in parallel circuit

  the same across each branch
• current in series circuit

  the same at all points
• current in parallel circuit

  add up to give the total current
• resistance in series circuit

  add up to give the total resistance
• resistance in parallel circuit


  the sum of the reciprocals of the individual resistances (1/RT=1/R1+1/R2+...)
• what does a straight line graph through the origin indicate about the relationship between current and voltage for a fixed resistor?

  proves that current and voltage are directly proportional for a fixed resistor
• is resistance constant in a torch bulb?

  no, as it's a non-ohmic conductor
• what happens when a torch bulb gets brighter?

  temperature and resistance increases
• transistor


  a voltage controlled electronic switch
• npn transistor

  switches on when the base-emitter voltage is ≥ 0.7 V
• mosfet


  switches on when the gate-source voltage is ≅ 2 V
• low temperature detection (thermistor in bottom position)

  - temperature decreases and the resistance of the thermistor increases

  - the voltage across the thermistor increases

  - when it reaches 0.7V, the transistor switches on and the bulb turns on

  - the circuit indicates low light levels