Main Points - Current Electricity

• The function of the open switch is to turn a circuit on or off. If open, the circuit is broken and turned off
• The function of a closed switch is to turn a circuit on or off . If closed, the circuit is complete and turned on
• Cell = A single electrical energy source which uses chemical reactions to produce an electrical current
• Battery = A combination of two or more cells
• Resistor = Restricts or limits the flow of electrical current. The resistance value is fixed and cannot be changed
• Variable resistor = The resistance is not fixed and can be changed
• Thermistor = The resistance value decreases as the temperature increases
• Light dependent resistor = The resistance value decreases as light levels increase
• Light emitting diode = Produces light when an electrical current flows through it in the forward direction
• Diode = Allows the flow of current in only one direction
• Bulb = Produces light when an electrical current flows through and heats the filament
• Fuse = A strip of wire or metal which melts when the electrical current increases beyond a certain 'safe' value
• Voltmeter = A device which is used to measure potential difference or voltage
• Ammeter = A device which is used to measure electrical current
• For an electrical current to work there needs to be a complete and unbroken path of components and a cell, battery or power supply
• When the electrical circuit is complete, voltage flows from the power supply causing charge to flow around the circuit
• The flow of charge is called current
• Electricity can be described as the movement of electrons which carry energy and travel through a wire/cable
• Current = The rate which electrical charge flows
• Charge = The number of charge carriers
• Voltage = The energy carried by each charge
• Electrical conductor = A material allows electrical charge to pass through it easily
• The two types of circuit are series and parallel
• Series circuit = one continuous loop where components are connected one after another
• Parallel circuit = one continuous loop with branches where components are connected alongside one another
• The component used to measure current is called an ammeter
• Ammeters are placed in series with the component they are measuring
• In a series circuit, the current is the same throughout the circuit. This is because there is only one path for the electrons to flow through.
• • In a parallel circuit, the current before a split is the same as the current after the spilt.
  • This is also the same as the total current from all the branches added together.
  • This is because current splits at branches and re-joins after as there are multiple paths for the electrons to flow through
• Voltage is also called potential difference
• The component that measures voltage is the voltmeter
• Voltmeters are placed in parallel around the component they are measuring
• In series circuit, the voltage of the power supply is shared amongst all the components. This is because there is only one path for the electrons to flow through so the voltage they carry must be shared amongst all components
• In a parallel circuit, the voltage of the power supply is the same as the voltage of each branch. This is because there are multiple paths for the electrons to flow through so the voltage they carry is not shared amongst every component
• Voltage = the energy transferred to a component by each charge that flows through it
• Resistance is the opposition from an electrical component/wires as electrical charge/current passes through it
• Resistance can be measured using an ammeter placed in series with the component they are measuring and a voltmeter placed in parallel around the component they are measuring
• The resistance required practical is:

  1.Assemble the circuit as shown in the circuit diagram

  2.Connect one crocodile clip at the zero end of the half-meter ruler

  3.Connect the other crocodile clip so that it is 10cm apart

  4.Record the readings on the voltmeter and ammeter at this length

  5.Repeat this process for the different lengths of wire to be tested

  6.Calculate the resistance of each length of wire using the equation: Resistance = Voltage/Current

  7.Plot the data on a graph to show how the length of the wire affects its resistance
• The conclusions of the resistance practical are:

  • As the length of wire increased, the resistance increased
  • Resistance is directly proportional to the length of the wire as the graph gives a straight line through the origin
• In a series circuit, the resistance increases when the number of resistors increases