Question

What should be the resistance of an ideal ammeter and ideal voltmeter?

Answer 1

Hint: For accurate measurement, an ammeter must have very small resistance and very large current carrying capacity and for the same reasons a voltmeter must have a very large resistance and very small current carrying capacity.

Complete answer:
An ammeter is an instrument which is used for measuring large electric currents in circuits. To measure the current, it is put in series with the electrical circuit in which the current is to be measured. It must be connected in series because the magnitude of current is the same in series circuit.
For accurate measurement, an ammeter must have very small resistance and very large current carrying capacity. For the ideal case, resistance of an ammeter is zero.
Therefore, ammeter is made by connecting resistance in parallel with the coil of a galvanometer. This parallel resistance is called shunt. Because of the shunt the overall resistance of the ammeter reduces and its current carrying capacity increases.
A voltmeter is used for measuring electric potential difference between two points in a circuit. To do this, it is put in parallel with the branch of circuit, for which the potential difference is to be measured.
For accurate measurements a voltmeter must have a very large resistance (infinite in ideal case) and very small current carrying capacity.
It is, therefore, made by connecting a high resistance in series with the coil of the galvanometer. The high resistance in series increases the overall resistance of the voltmeter and reduces its current carrying capacity.

Note: Both ammeter and voltmeter are made by adding shunt in parallel and in series respectively with the galvanometer. Ammeter is used in series with the branch in which current is to be measured while voltmeter is connected in parallel to the branch along which potential difference is to be measured.