Any material has at least a little bit of electrical resistance(except supercond

Question

Any material has at least a little bit of electrical resistance(except superconductors...but they only exist at very lowtemperatures). Even the regular wires in a circuit (which weusually model as resistance-less) technically have a tinybit.

Your job here is to consider two common measurement devices: anammeter and a voltmeter. A well-built ammeter should have as littleinternal resistance as possible. A well-built voltmeter should havea huge internal resistance.
My question is why is the above statement true. I dontunderstand.

Please use the above picture as the sample case. What would happenif the ammeter had a significant internal resistance? How would thecircuit be messed up if the voltmeter had a tiny internalresistance?

Explanation / Answer

First, an ammeter measures the current through a circuit. Ifan ammeter has a large resistance, that needs to be calculated intothe the total resistance of the circuit since when you measurecurrent, current must go through the ammeter. Since you wouldneed to add in this resistance, it would change the totalresistance and change the total current along with the current ineach branch. This all happens because as current is measuredby an ammeter, the current must go through the ammeter. Inthe above diagram, if the ammeter had significant internalresistance, less current would flow through that branch. The voltmeter measures the voltage drop from one place toanother. You need this to have a large resistance because youdo not want current to go through it (the majority of current takesthe path of least resistance when there is a choice). Bycreating a large resistance, you ensure that current will continueto flow in the way that it was going and it is just measuring thedifference in voltage from one place to another. If thevoltmeter had very small resistance, you are essentially creating ashort circuit in the above diagram and current would not be flowingin the same way. Hope that helps

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