precision and Accuracy

[XPFMember]

Assalamoalaikum!!
I am really confused about it...can somebody plz explain it!
JazakALlah Khairen!

 

[larina]

Walaikumusalam

precision:- it is the values which areclose together ex. measuement of a table; 3.55 m or 3.50m or 3. 58m...these all measurements are close eash other so we say that they are precise. the more u repeat the more precise value u get.

accuracy:- it is the measurement which is very close to the true value...it is applied on the measuring instrument

 

[XPFMember]

JazakAllah Khairen!

 

[anzaar]

The Distinction between Precision and Accuracy:
Precision: Precision is that part of accuracy which is within the control of experimenter. The experimenter may choose different instruments and may use them with different levels of skill, thus affecting the precision of measurement. So precision refer to the extent or limit of sensitivity of a given measuring instrument to obtain readings of the physical quantity being measured. For example, a meter rules can be used to obtain length measurements with precision up to 0.1cm while vernier calipers up to .01cm whereas micrometer screw gauge has a precision of up to 0.001 cm. Obviously a micrometer screw gauge is more precise instrument compared to a meter rule. This implies that degree of precision has been made increase as we move from a meter rule to screw gauge
Note:
i) Number of significant figures quoted for the measurements increase as the precision increase. In fact number of significant figures in a measurement gives indication of the precision of the measurements.
ii) Using measuring instrument with less precision means that there would be greater spread of readings resulting in greater uncertainty.
iii) A reading may be precise but it need not be accurate.
Accuracy: A measurement is said to be accurate if it is close to the actual value. Accuracy depends on the equipment used, the skill of the experimenter and techniques used. Accuracy is concerned how close a reading is to its true value. Hence accuracy refers to the value of a measured quantity. This accuracy depends on the magnitude of the quantity measured and the types of instrument used.
For example: using a meter rule to measure a length of 1 cm will incur an uncertainty of length up to 10|%(0.1 out of 1cm). However the same meter rules used to take length measurements of up to 100 cm will result in an uncertainty of only 0.1%. Thus the same instrument with given precision used to measure quantities of different magnitudes, will give rise to different accuracy.

 

[XPFMember]

@anzaar:If possible can u give examples using different set of values

 

[anzaar]

Example:

an amp-meter with a three-digit display is more precise than an amp-meter with a two-digit display. With a 30 cm ruler, you can usually measure the distance of an object down to the closest millimeter, and perhaps even down to a quarter of a millimeter. Such a means of measuring is not as precise as if you were using a micrometer to measure the same distance. Additionally, a poorly calibrated micrometer is still more precise than a 30 cm ruler.

Example:
consider a 100 gram block of wood. We are told that this block has a mass of 100 grams. Now, if we put it on balance A, we get a mass of 99.9 grams. When we put it on balance B, we find a mass of 101.350022. We can say that balance A provides us with a more ACCURATE number because it is closer to the known mass of 100 g, but balance B gives us a much more PRECISE number because it displays more decimal places. However, even with the extra decimal places, it isn't as accurate as balance A. (Maybe there is something wrong with its calibration?)


Example: the speedometer of a Golf is calibrated with ticks every 5 km. Thus, I could estimate that my speed is 59 km/h, or, at the same time, I could estimate that my speed is 58.888483 km/h. As the actual speed may be 58.959383⋅⋅⋅ km/h, we note that the error between both approximations and the actual speed are 0.040617 and -0.0709 and therefore both answers have approximately the same accuracy. It may be that the actual speed is closer to one of the two answers, but this would be coincidence.
example:
If we measure the length of a foot-ruler and get values of

12.01 in, 12.00 in, 11.99 in, 12.00 in.

These numbers are precise enough for us to believe that if we measure it again we would get 12.00+0.01 in. These measurements are precise but necessarily accurate. The foot-ruler may actually be metric ruler of 30.0 cm long. Our measurement is precise but not accurate.


hoping that you have got the concept.

 

[hassam]

GR8 explanation anzaar...

 

[anzaar]

i tried to make it more clear