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
