Science revision

Current and Voltage in Electical Circuits

Circuits

Electrical circuits can be represented by circuit diagrams. The various electrical components are shown by using standard symbols in circuit diagrams. Components can be connected in series, or in parallel. The characteristics of the current and potential difference (voltage) are different in series and parallel circuits.

Circuit Diagrams

Two things are important for a circuit to work:

  • There must be a complete circuit
  • There must be no short circuits

To check for a complete circuit, follow a wire coming out of the battery with your finger. You should be able to go out of the battery, through the lamp, and back to the battery.

To check for a short circuit, see if you can find a way past the lamp without going through any other component. If you can, there is a short circuit and the lamp will not light.

Series and Parallel Circuits

Series connections

Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows across each component connected in series is the same. Also, if there are two or more lamps and one of them breaks then the others will stop working aswell because there is no alternative route for the current to flow.

Parallel connections

Components that are connected on separate loops are connected in parallel. The current is shared between each component connected in parallel. This means that if there is one lamp on the first loop and another on the second loop and the first lamp breaks then the current can still go through the second loop and make the second lamp work still

Electric current

Electric current is a flow of electric charge. No current can flow if the circuit is broken

- for example, when a switch is open.

Measuring current

Current is measured in amperes (which is often abbreviated to amps or A). The current flowing through a component in a circuit is measured using an ammeter. This must be connected in series with the component.

calculating current

What is the current if 20 C of charge passes in 5 s?

  • Current = 20 ÷ 5 = 4 A
  • Potential difference

    A potential difference, also called voltage, across an electrical component is needed to make a current flow through it. Cells or batteries often provide the potential difference needed.

    Measuring Potentail difference

    Potential difference is measured in volts, V. The potential difference across a component in a circuit is measured using a voltmeter. This must be connected in parallel with the component.


    calculating Potential difference

    What is the potential difference if 48 J of energy is transferred when 4 C of charge passes?

    Potential difference = 48 ÷ 4 = 12 V