# Sources of Error in Standing Waves Lab

1. Nov 13, 2005

### dekoi

I have to write an error analysis for my lab report, but am having some trouble making my sources of error clear and precise. The lab itself was a very basic investigation of the relationship between the tension, frequency, and mass per unit length (mu) in a standing wave pattern.

Some thoughts:

-improper measurement of string
-improper measurement of frequency (that is, the value read from the machine is too high or low, hence producing a large percentage of error)
-incorrect visual observation of the number of loops; for example, 4 loops mistaken for 3
-mistake in calculation

Any thoughts would be very helpful from experienced members.

2. Nov 13, 2005

### andrevdh

Did you alter the tension in the string (pulley and masses or lever) and determined the frequency of the oscillation at the specific tensions? How did the higher harmonics (loops) originate, did you induce them? Did you change the strings and repeated the experiment? Was the linear density given or did you measure it yourself?

3. Nov 13, 2005

### dekoi

We did alter tension. The frequency was read from a machine. We induced the higher harmonics. We did not change the string. Linear density was measured.

4. Nov 14, 2005

### andrevdh

The term error in an measurement causes great confusion. Nowadays the term uncertainty in a measurement is rather used. This means any factor that could possibly cause a measure of uncertainty in a measurement should be identified. By a measure of uncertainty I mean that the numerical value of the measurement has a percentage of uncertainty asssociated with it - the measurement is not 100% accurate. Due to some factor influencing the measurement (this is what you are trying to identify) it is probably off by some percentage from the real value of the measurement. Countable quantities (like the loops) have no uncertainty in them - they are 100% accurate since we all can agree on such quantities, but measurements can be off from the real value. In order to help you I need to know more about the experiment though. Which was the independant variable of the experiment, the tension? Was the one end of the string (metal?) fixed to the tension device (how was this changed) an the other end tied to a vibrating device? Did you alter the frequency? Do you need to quantify the errors in your measurements for the error analysis?

Last edited: Nov 14, 2005