In a 9V circuit, all the resistors are 20 or 40 kilo Ohms.
Convention says that calcs should therefore be quoted to 1 sig fig, since the volts are the least accuracy.
2 seems better though. Any ideas?
Carrying an extra sig. fig. is always a good idea, since the first significant digit of whatever you are computing (such as current in this case) may be a low one like 1 or 2.
1 +/- 0.5 is precision, but 9 +/- 0.5 is 0.55% precision.
When dealing with calculations involving resistors in a circuit, it is important to consider the accuracy and precision of the measurements involved. In this case, all the resistors in the circuit have values of either 20 or 40 kilo Ohms. The voltage provided by the circuit is given as 9V.
Conventionally, when performing calculations, it is best to refer to the measurement with the least accuracy or precision. In this case, since the voltage is given as 9V, it is expected that the voltage measurement has the least accuracy.
According to the convention, when dealing with calculations involving measurements with different levels of accuracy, you should quote the final result with the same number of significant figures as the least precise measurement. In this case, since the voltage measurement has only one significant figure, the convention would suggest quoting the final result with one significant figure as well.
However, in some cases, using only one significant figure may not provide enough accuracy. It is generally more common and appropriate to use at least two significant figures, unless there is a specific reason to limit the significant figures.
To summarize, based on convention, you should quote the final result with one significant figure, considering the least accurate measurement, which is the voltage in this case. However, it is often better to use at least two significant figures to increase the accuracy of your calculations, unless there are specific circumstances that require stricter adherence to the convention.