I was performing a basic verification of Ohm's law in a DC circuit experiment the other day, during my exams and I mistakenly used an ammeter with range 0-10A instead of the 0-1A ammeter that the practical manual expects us to use.
The invigilator/examiner noticed this error and told me that this is a really bad error on my part and this will not be forgiven. She cut half my marks just because of this small error(?). I retorted by saying that it shouldn't really matter, because all I am doing is just reading the current value in the circuit and the range of the ammeter used won't affect that value. She said that isn't the case and the range of the ammeter WILL affect the current reading. I didn't know much of the specifics about the working of an ammeter, so I just ignored her. I don't even care about the marks too.
All I want to know is whether the range of the ammeter affects the current reading shown by it? If possible, I also want to know how the current value is affected just by swapping it out with an ammeter of a different range.
I looked up the working of an ammeter and I found that an ammeter is just a galvanometer with a resistance in parallel (I don't understand what they mean by parallel). Maybe the resistance increases the overall resistance of the circuit and hence leads to decrease in current(?). Please let me know if my speculation is correct or not. Thanks in advance for tolerating my zero knowledge of the subject 🙂
Best Answer
Yes it does matter a little. Say you have a speedometer that is 0-1000 mph scale You also have a scale of 0 to 10 mph
You are walking 1mph, which scale would be most accurate, of course the 0 to 10.
All meters scales are like this, the 0 to 1000 would still measure but not as good as the lower scale.