ok so we were doing this experiment which as we were changing voltage we took note of the current in the circuit. By dividing voltage to current we got resistance. Also we measured the Resistance by using some thing( I don't know what it was:D) and the two Numbers we got for resistance weren't the same. So what could be the error?
Is it due to the resistance of cables and the other heating up of wires? Could these two be the source of error? which results in changing resistance? Please if u want more details I will add
Sorry about m,y English :)
Is it due to the resistance of cables and the other heating up of wires? Could these two be the source of error? which results in changing resistance? Please if u want more details I will add
Sorry about m,y English :)
-
The most accurate measurement of resistance requires a 4-terminal setup. You pass the current through 2 terminals and measure the voltage across the other 2, then you do not include the resistance of the current-sourcing terminals in your calculation.
If you used a resistance meter, that probably passes a small current and measures the voltage. You can zero the meter by measuring the resistance between the two probes and adjusting the zero offset. A modern DVM uses so small a current that there is probably no noticable error.
You can also get errors due to surface effects - where the metals of the probes touch the resistance under test, there can be small voltages developed due to oxide layers or just having dissimilar metals.
As you say, heating may be an issue. You can repeat the measurements using different currents and then plot the voltage against current on a graph. An ideal resistance should give a straight line through zero, while a DC offset indicates a surface effect and curvature indicates nonlinearity, like heating.
More data points will show up outliers (mistakes) and increase statistical accuracy.
If you used a resistance meter, that probably passes a small current and measures the voltage. You can zero the meter by measuring the resistance between the two probes and adjusting the zero offset. A modern DVM uses so small a current that there is probably no noticable error.
You can also get errors due to surface effects - where the metals of the probes touch the resistance under test, there can be small voltages developed due to oxide layers or just having dissimilar metals.
As you say, heating may be an issue. You can repeat the measurements using different currents and then plot the voltage against current on a graph. An ideal resistance should give a straight line through zero, while a DC offset indicates a surface effect and curvature indicates nonlinearity, like heating.
More data points will show up outliers (mistakes) and increase statistical accuracy.
-
I think that it would be more likely the resistance itself. When current flows through a resistance, it heats up, therefore, the resistance changes.(1st time, resistance could have been colder)
Like you said, It may also be due to wires heating up(depending the wire diameter)
(Too much Amps through a too small wire)
Like you said, It may also be due to wires heating up(depending the wire diameter)
(Too much Amps through a too small wire)
-
Internal resistance of the wire is a reason as ohms law is meant specifically for ideal wires. Another reason for error could be that voltmeter took up some of the current (as it is wired in series), this means that a perfect reading of the voltage across the element was not achieved.