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Introduction

A kettle heats water because of an electric current passing through the kettle element. The designer must design it to boil water as quickly as possible. A big current and voltage means more energy gets into the water faster. In the UK, a kettle can draw no more than 13 A with a rated mains supply voltage of 230 V. The designer uses an ammeter to check her kettle current, and a voltmeter to check the voltage.

Task 1: Measuring voltage


Model 1

  1. Open the Yenka Model 1.
  2. Add a voltmeter to the simulation from the Lab Equipment > Measurement folder.
  3. Drag a wire from each end of the meter. Place one wire at A and one at B.
  4. Read the voltage and make a note of it. If the reading is negative, you have connected it the wrong way round. Either turn the voltmeter round, or cross the connecting wires over.
  5. Draw a circuit diagram for a circuit to measure the voltage across L2. Use circuit symbols.
    Answer

    Answer
  6. How many extra wires do you need to bring to the circuit?
    Answer
    Two.
  7. Do you need to break into the circuit to use a voltmeter?
    Answer
    No.
  8. How could a poorly designed voltmeter affect the current in the circuit?
    Answer
    Low resistance pathway would allow current to by-pass bulb.

Summary

A voltmeter must be connected in parallel with a component - we often describe it as 'connecting across' the component. It should have as high a resistance as possible to stop it affecting the circuit.

Task 2: Measuring current

  1. Keep Yenka Model 1 open.
  2. Disconnect the wire between B and C.
  3. Place an ammeter in the gap between B and C. Connect its terminals to B and C with new wires.
  4. If the reading on the ammeter is negative, you have connected it the wrong way round. Either turn the ammeter round, or cross the connecting wires over.
  5. Draw the circuit diagram for the circuit you have just made. Use circuit symbols.
    Answer

    Answer
  6. Do you have to break into the circuit to make it work?
    Answer
    Yes.
  7. How many extra wires do you need to bring to the circuit?
    Answer
    One.
  8. How could a badly designed ammeter affect the current in the circuit?
    Answer
    High resistance reduces current in circuit.

Summary

An ammeter must be connected in series with other components in a circuit. This means you add an ammeter in much the same way that you add a new daisy into a closed daisy chain. An ammeter should have as low a resistance as possible to stop it affecting the circuit.

Teacher Summary

  • This activity is complemented by the activity Using Ammeters and Voltmeters, which gives practice measuring the voltage and current in some simple circuits.