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InterviewSolution
| 1. |
Why should the resistance of:a) an ammeter be very small ?b) a voltmeter be very large ? |
| Answer» An\xa0ammeter\xa0has to measure to current flowing through the circuit. Resistance offers an obstruction to the current flow. So, if the resistance of an ammeter is large , the current measured by the ammeter will be quite less as compared to the actual amount of current flowing through the circuit which is undesirable. If ammeter has\xa0zero resistance\xa0, then it will give the exact value of current. But this is not practically possible because every material has some value of\xa0internal resistance\xa0which we can\'t control. For this reason , ammeter must have small resistance.Voltmeters\xa0are put in parallel with the load in order to measure the\xa0potential difference between two *different* points. If they are in parallel with the load, then at the first junction the current will split and flow into both paths (Kirchhoff\'s Laws). However, if current is flowing through the voltmeter, then it is not all flowing through the load, and the potential difference across the load would change when the voltmeter is added and removed. This is unfavourable. Therefore, the voltmeter must have a very high resistance so that current doesn\'t flow through it. | |