Use of Digital Instruments (OCR A Level Physics): Revision Note

Use of Digital Instruments

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

Digital Instruments Table

• 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

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

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