Question

I cannot understand example no. 2.6 in the chapter units and dimensions. The page no. is 25 in Ncert textbook. Can you please explain it to me? The question starts with:-

Two clocks are being tested.....

Answer 1

We know that clock 2 is more precise as its readings are very close to each other but they are very far from the actual reading because of the zero error in the clock. Moreover, as the zero error can be easily corrected thus it will be better to use the clock 2.
On the other hand
even though the clock 1 is more accurate but not precise thus it can not be preferred for experiments as the error (instrumental error) by the clock cannot be corrected.
It means,
For clock 1: Highest variation = 12:01:50 I.e, reading has gone up by 110 seconds Lowest variation = 11:59:15 I.e, reading has gone down by 52 seconds Therefore, the total variation = 110 + 52 = 162 seconds Use the same Method for clock 2 and find the variation . We observe that clock 2 has a comparatively lower variation. Thus clock 2 is a better pick.



Another way to explain is........

we measure the time at 12 o clock each noon.
So the variations in time of each clock from the standard time of 12:00:00 is calculated.
We find that the maximum variation in clock 1 is 162 second and in clock 2 is 31 second
Even though the average time of clock one is more closer to the actual time of 12:00:00,
but the variation in time interval is more in clock 1 as compared to clock 2.
It means clock 2 is more accurate in maintaining the time intervals as compared to clock 1.
Clock 2 has a zero error. i.e. its time has an error of a constant quantity which can anytime be compensated to give good and more accurate results.