Circuits

Basic Concepts in Circuits

  • Circuits are created by using a power source (usually a battery or mains electricity), a load (something that uses electricity like a light bulb or a motor), and wire to connect them all together.
  • A circuit can be open (electricity can’t flow) or closed (electricity can flow).
  • Electricity flows from the positive terminal to the negative terminal.
  • Conductors are materials that allow electric current to flow through them easily, while insulators do not allow electric current to flow easily.

Circuit Diagrams

  • Circuit diagrams are simplified representations of an electrical circuit.
  • Component symbols are used to represent different parts of the circuit such as resistors, capacitors and inductors.
  • In a circuit diagram, the battery is represented by one long and one short parallel lines, the light bulb is represented by a circle with a cross inside, and the wire is represented by a line.

Current and Voltage

  • Current is the flow of electrons in a circuit, measured in Amperes (A). It’s shown by an ‘I’ in equations.
  • Voltage is the energy per unit charge, measured in Volts (V). It’s shown by a ‘V’ in equations.
  • The formula linking current, voltage and resistance is V = I x R. This is called Ohm’s Law.

Series and Parallel Circuits

  • A series circuit is a circuit where there is only one path for the electrons to flow. If one component breaks or is switched off, all components will stop working.
  • A parallel circuit is a circuit where there is more than one path for the electrons to flow. If one component breaks or is switched off, the others can still work.
  • In a series circuit, the total resistance is the sum of the individual resistances (Rtot = R1 + R2 + …). In a parallel circuit, the total resistance is given by 1/Rtot = 1/R1 + 1/R2 + … .

Measuring Electricity

  • An ammeter measures current and must be connected in series.
  • A voltmeter measures voltage and must be connected in parallel around the component of interest.
  • Resistance measures how difficult it is for the electric current to pass through a component, measured in Ohms (Ω). A device called an ohmmeter is used to measure resistance.

Energy Use and Power

  • The energy transferred to an electrical appliance depends on its power and the length of time it is on. This is given by the formula E = P x t.
  • Power is the rate at which energy is transferred, measured in Watts (W). It is given by the formula P = V x I.
  • The cost of electricity can be calculated by multiplying the energy consumption (in kWh) by the price per unit of electricity.