Question

If an ammeter is to be used in place of a voltmeter. Then we must connect with the ammeter
A) A low resistance in parallel
B) A high resistance in parallel
C) A high resistance in series
D) A low resistance in series

Answer 1

Hint : An ammeter is essentially a low resistance galvanometer that is connected in series with a circuit element. On the other hand, a voltmeter is essentially a very high resistance galvanometer that is connected in parallel with a circuit element.

Complete step by step solution :
An ammeter can be considered to be a very low resistance galvanometer that is connected in series with the circuit element through which the current has to be measured, whereas a voltmeter can be considered to be a very high resistance galvanometer through which no current passes and is connected in parallel to the circuit element across which the voltage has to be measured.
Hence, to use an ammeter in place of a voltmeter, we have to somehow make the resistance of the ammeter very high and ensure that current does not flow through it but through a parallel branch.
We can do this by connecting an extremely low resistance in parallel with the ammeter. In this way the ammeter will have a very high resistance relatively and most of the current will pass through the parallel branch having the extremely low resistance. Therefore, the ammeter will essentially become a high resistance galvanometer connected in parallel with the circuit element. Therefore, going by the explanation given above for a voltmeter, the ammeter can now be used equivalent to a voltmeter.
Hence, the correct option is A) A low resistance in parallel.

Note : Students must remember that to convert a galvanometer into a voltmeter, a high resistance is added along with the galvanometer in series forming a combined voltmeter setup. This increases the voltage range of the voltmeter setup as most of the voltage drop is across the high resistance. Similarly, to convert a galvanometer into an ammeter, a very low resistance must be added in parallel to form a combined ammeter setup. This increases the current range of the ammeter as a lot of current flows through the low resistance branch.