Electricity and Circuits

• • Current is the movement of electrons
  • It is measured in amperes (A)
  • The current has the same value at every point in a single closed loop
• Current = charge/time
• • An electrical conductor is material that allows electric current to pass through it
  • All metals are electric conductors
• • An electric insulator is a material that doesn't allow electric currents to pass through it
  • Plastic and glass are electrical insulators
• • An electric conductor has lots of charges that are free to move
  • In a metal the charges that are free to move are electrons
  • The electric current through the metal is the flow of these free electrons
• • An electrical insulator has no free electrons
  • No charges are free to move and carry a current
• • Potential difference is measured in volts and can be called voltage
  • Potential difference is energy transferred per coulomb of charge that passes between two points in an electrical circuit
  • It is measured using a voltmeter
• Voltage = energy/charge
• • An ammeter measures the flow of current that passes through it
  • Ammeters have to be connected in series with the electrical component when measuring current
• • Voltmeters measure potential difference between two points in a circuit
  • Voltmeters must always be connected in parallel
• The difference between current and potential difference:

  • Current is a flow of charge measures through a component
  • Potential difference is the energy used between two points in a circuit therefore it is measured between two points either side of a component
• The size of a current is affected by:

  • the resistance: if resistance increases, the current decreases
  • the potential difference: if the potential difference increases, the current will increase
• Resistance is measured in ohms
• Resistance is the measure of how difficult it is for current to flow through a component
• Resistance = potential difference/current
• To measure the resistance of the component, measure the potential difference across the component and the current flowing through the component
• • Increasing the length of a wire increases the resistance of the wire
  • Decreasing the cross sectional area of the wire increases its resistance
  • Short, wide wires have less resistance than long, narrow wires
• • Charge flows from the energy source and through the rest of the circuit and its components (like lamps and heaters)
  • The flow of current transfers energy from the energy source to the component
  • The components then transfer energy to their surroundings
  • For example, a lamp emits light to its surroundings
  • The amount of energy transferred (joules) = charge moved (coulombs) multiplied by potential difference (volts)