Using Appropriate Instruments & Techniques (OCR AS Physics) : Revision Note

Using Appropriate Instruments & Techniques

• Being familiar with how to use a wide range of experimental and practical instruments is essential for both practicals and written exam questions

• Scientific instruments can be digital or analogue

Analogue

• Analogue scientific instruments transfer information through electric pulses of varying amplitude

  • This means they cannot be read easily by a computer

• Analogue instruments are cheaper but they have lower accuracy and resolution

• They are also more sensitive, which can make it difficult to read fluctuating values

• An analogue display normally involves a pointer which indicates a value depending on its position or angle on the scale

  

  Analogue meter

• The measurements taken on this analogue ammeter are restricted over a range e.g. 0 - 10 A and a resolution of 1 A

• Analogue meters are subject to zero errors

  • This means the marker must be double-checked before each reading. If it is not at zero, then the value but be subtracted from all the measurements

• They are also subject to parallax error

  • Always read the meter from a position directly perpendicular to the scale

• A potentiometer is an example of a sensitive analogue meter

Digital

• Digital scientific instruments translate information into binary (0 or 1) format which can then be read and analysed by a computer

• They are more expensive but have greater accuracy and resolution than analogue

• Digital displays show the measured values as digits

• They’re easy to use because they give a specific value and are capable of displaying more precise values

Digital meter

• The measurements taken on this digital ammeter have a much wider range and a resolution of 0.01 A

• Digital meters are also subject to zero error

  • Make sure the reading is zero before starting an experiment, or subtract the “zero” value from the end results

• Most digital meters have an auto-range function, this means it can show very low or very high values depending on the readings

  • This saves time selecting an instrument with the correct range and precision for your experiment

• A digital multi-meter is an example of a digital meter