Electricity

• Open switch

  
• Closed Switch

  
• Lamp

  
• Voltmeter

  
• Ammeter

  
• Resistor

  
• LDR

  
• Thermistor

  
• variable resistor

  
• Diode

  
• Light emitting diode (LED)

  
• Fuse

  
• Cell

  
• Battery

  
• Switch

  A switch used to turn a circuit on (closed) and off (open)
• Lamp


  An electrical current heats the filament in a bulb so that it gives out light.
• Fixed resistor

  A resistor restricts or limits the flow of electrical current. A fixed resistor has a resistance that does not change.
• Variable resistor

  Moving the position of the slider on this resistor, changes the resistance. A variable resistor is used in some dimmer switches and volume controls.
• Thermistor

  The resistance of a thermistor depends on its temperature. At low temperatures, the thermistor has a high resistance. As the temperature increases, the resistance decreases. A thermistor can be used in thermostats or heat activated fire alarms.
• Light-dependant resistor (LDR)


  The resistance of a LDR depends on light intensity. At low light levels, the LDR has a high resistance. As the light intensity increases, the resistance decreases. A LDR can be used as a sensor in cameras or automatic lights that come on when it gets dark.
• Direct current


  The flow of electrons is consistently in one direction around the circuit.
• An alternating current


  The direct of electron flow continually reverses
• Electrons are negatively charged particles and they transfer energy through wires as electricity.
• What is charge

  A property of a body which experiances a force in an electric field
• Electrical current is the rate of flow of electric charge.
• When current flows, electrical work is done and energy transferred. The amount of charge passing a point in the circuit can be calculated using the equation:
• Charge = current x time
• An ammeter is placed in series
• The voltmeter is placed in parallel
• The current through a component depends on both the resistance of the component and the potential difference across the component.
• What does the voltmeter measure

  To measure the component's potential difference
• Potential difference (or voltage) is a measure of energy, per unit of charge, transferred between two points in a circuit. A potential difference of 1 volt means that 1 joule of work is done per coulomb of charge.
• Potential difference = energy / charge
• Potential difference = current x resistance
• In a series circuit, if one of the components is broken, the current will not be able to flow all the way round - if one component goes out, they all go out
• A series circuit is one loop; all electrons in that loop form one current. An ammeter will measure the same current wherever it is placed in the circuit.
• In parallel circuits, electrical components are connected alongside one another, forming extra loops.
• in a parallel circuit, if one component goes out, the charge can flow through the other wires - only one component will go out
• As electrons flow through wires, they collide with the ions in the wire which causes the ions to vibrate more. This increased vibration of the ions increases the temperature of the wire. Energy has been transferred from the chemical energy store of the battery into the internal energy store of the wire.
• Power = current x potential difference