About Lesson
Accuracy and Precision of Instruments
- Any uncertainty resulting from measurement by a measuring instrument is called error. They can be systematic or random.
- Accuracy of a measurement is how close the measured value is to the true value.
- Precision is the resolutionor closeness of a series of measurements of a same quantity under similar conditions.
- If the true value of a certain length is 3.678 cm and two instruments with different resolutions, up to 1 (less precise) and 2 (more precise) decimal places respectively, are used. If first measures the length as 3.5 and the second as 3.38 then the first has more accuracy but less precision while the second has less accuracy and more precision.
Types of Errors- Systematic Errors
Errors which can either be positive or negative are called Systematic errors. They are of following types:
- Instrument errors: These arise from imperfect design or calibration error in the instrument. Worn off scale, zero error in a weighing scale are some examples of instrument errors.
- Imperfections in experimental techniques: If the technique is not accurate (for example measuring temperature of human body by placing thermometer under armpit resulting in lower temperature than actual) and due to the external conditions like temperature, wind, humidity, these kinds of errors occur.
3. Personal errors: Errors occurring due to human carelessness, lack of proper setting, taking down incorrect reading are called personal errors.
These errors can be removed by:
- Taking proper instrument and calibrating it properly.
- Experimenting under proper atmospheric conditions and techniques.
Removing human bias as far as possible
Random Errors
Errors which occur at random with respect to sign and size are called Random errors.
- These occur due to unpredictable fluctuations in experimental conditions like temperature, voltage supply, mechanical vibrations, personal errors etc.
- Smallest value that can be measured by the measuring instrument is called its least count. Least count error is the error associated with the resolution or the least count of the instrument.
- Least count errors can be minimized by using instruments of higher precision/resolution and improving experimental techniques (taking several readings of a measurement and then taking a mean).