3. Electricty

• Cell

  
• Battery

  
• Switch Open

  
• Switch Closed

  
• Filament Lamp/Bulb

  
• Fuse

  
• LED

  
• Resistor

  
• Variable Resistor

  
• Ammeter

  
• Voltmeter

  
• Diode

  
• LDR

  
• Thermistor

  
• Cell/Battery

  Provides the circuit with a source of potential difference. A battery is made up of two or more cells
• Switch

  Turns the circuit on (closed) or off (open)
• Fixed Resistor

  A resistor limits the flow of current, a fixed resistor has a resistance it cannot change
• Variable Resistor

  A resistor with a slider that can be used to change its resistance, these are often used in dimmer switches and volume controls
• LDR (Light-Dependent Resistor)


  The resistance of an LDR depends on the light intensity, as the light intensity increases, its resistance decreases (vice versa)
• Diode

  Allows current to flow in one direction only, they are used to convert AC to DC current
• LED (Light-Emitting Diode)


  Emits light when a current passes through it, these are used for aviation lighting and displays (TVs, road signs)
• Ammeter

  Used to measure the current in a circuit, it is connected in series with other components
• Voltmeter

  Used to measure the potential difference of an electrical component, it is connected in a parallel with the relevant component
• Electric Current

  The flow of electrical charge
• Current

  Measured in Amps, A

  Measured by : Ammeter

  Symbol is $I$
• The size of the electric current is the rate of flow of electrical charge

  (How much charge passes through a point each second)
• The current in a circuit is a flow of electrons
• Charge

  A quantity of charge that passes a fixed point per second when a current of 1A is flowing
• Charge

  Unit is Coulombs, $C$
• 1C = 1A (1C is equal to one second by a current of 1A)
• Charge example question :

  A battery charger passes a current of 2.0A through a cell over a period of 2.5 hours. How much charge is transferred to the cell?

  • $Q=$$It$ -> 2.0 x (2.5x60x60)
  • Answer : 18,000C
• For electrical charge to flow through a closed circuit, it must include a source of potential difference (p.d)
• Sources of Potential Difference are:

  • A cell
  • Batteries
  • Electrical generator
• Potential Difference

  Also known as Voltage

  Measured in/Symbol : Volts, $V$
• Potential Difference

  The energy transferred per unit charge flowing from one point to another
• Energy transferred also known as Work Done


  Equation for P.D : $V=$$W/Q$

  (V=P.D, W=Work Done (J), Q=Charge (C)
• Potential Difference is measured by a Voltmeter

  Voltmeters are always set up in parallel circuits
• Charge equation

  $Q=$$It$

  (Q=Charge (C), I=Current (A), T=Time (s)

  
• Current in a Loop

  • Electrons flow away from the negative terminal of a cell towards the positive terminal
  • Convectional charge is opposite to the direction of electron flow
• Conventional Current

  The flow of positive charge from the positive terminal of a cell to the negative terminal