OCR A Level Physics

Revision Notes

1.3.3 Use of Digital Instruments

Test Yourself

Use of Digital Instruments

  • The type of digital instrument needed depends on the measurements to be made:

Digital Instruments Table

Digital Apparatus Table, downloadable AS & A Level Physics revision notes

  • Note that the top-pan balance doesn't necessarily measure the mass of an object directly, but its weight
    • The mass can then be calculated using the equation W = mg where W is the weight and g is the acceleration due to gravity (9.81 m s-2)

Digital Multimeter

Multimeter, downloadable AS & A Level Physics revision notes

A digital multimeter

  • A digital multimeter is capable of measuring voltage, current and resistance
    • Therefore, it can be used as a voltmeter, ammeter or ohmmeter

  • These are often used because it is very hard to measure very small currents and voltages on standard digital ammeters and voltmeters (especially of the order of mA or μA)
  • The advantage of a multimeter is that it can measure a greater range of readings from μA to kA (same for volts and Ω)
  • This is done by turning a dial in the middle to the appropriate ammeter, voltmeter or ohmmeter setting
    • However, if the dial is set at a small current setting, but a very large current is measured instead, this will blow the fuse in the multimeter and it will have to be replaced
    • Therefore, it is important the correct range of currents or voltages is estimated before setting the dial

  • Most of the time, the multimeter will be set to measure a DC voltage
  • It is important to remember to turn off the multimeter after use so the battery doesn't run out

Multimeter example 1, downloadable AS & A Level Physics revision notesMultimeter example 2, downloadable AS & A Level Physics revision notes

How to use a multimeter to measure the resistance of a resistor

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