- #1

mishima

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Hi, I am confused about when the rule for counting uncertainty applies. I know for radioactivity experiments one expresses the uncertainty (error) in the decay count as the square root of the count. So if you counted n decays you would report an average rate of

[itex]n \pm \sqrt{n}[/itex]

I was wondering if the same technique applies to, for example, a pendulum whose frequency is calculated based on the number of oscillations in a given time. So perhaps you just watch while holding a stopwatch, or maybe you use a photogate and allow the computer to record breaks in the voltage.

A. The reason I think it doesn't is because the pendulum oscillations are not random like radioactivity. If that is the case, what is the procedure for correctly reporting uncertainty in the frequency calculation?

B. The reason I think it might still apply is because using the square root of the count gives an

C. This is a bit of a tangent, but how would the error reporting scheme (whatever it is) change if I used the method of counting with my eyes and a stopwatch vs a photogate attached to a computer?

Thanks for any insight.

[itex]n \pm \sqrt{n}[/itex]

I was wondering if the same technique applies to, for example, a pendulum whose frequency is calculated based on the number of oscillations in a given time. So perhaps you just watch while holding a stopwatch, or maybe you use a photogate and allow the computer to record breaks in the voltage.

A. The reason I think it doesn't is because the pendulum oscillations are not random like radioactivity. If that is the case, what is the procedure for correctly reporting uncertainty in the frequency calculation?

B. The reason I think it might still apply is because using the square root of the count gives an

__average__rate. Like, if one repeated the decay experiment many times, you would certainly NOT get the same specific count each time. However, the discrepancy between the average rate would likely be insignificant. Similarly with the pendulum, in a crude setup (like in a high school lab) wouldn't you expect variation in the specific counts yet an existent average rate?C. This is a bit of a tangent, but how would the error reporting scheme (whatever it is) change if I used the method of counting with my eyes and a stopwatch vs a photogate attached to a computer?

Thanks for any insight.

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