Final answer:
The ideal input resistance of an ammeter should be as close to zero as possible to minimize its effect on the circuit being measured. Thevenin's equivalent circuit can help understand this concept.
Step-by-step explanation:
The ideal input resistance of an ammeter should be as close to zero as possible. This is because an ammeter is used to measure current, and having a high resistance would affect the current flowing through the circuit being measured. Thevenin's equivalent circuit can be used to understand this concept.
In Thevenin's equivalent circuit, a voltage source is connected in series with an equivalent resistance. When this circuit is connected to a load, the current flowing through the load will be determined by the equivalent resistance. Therefore, to minimize the effect of the ammeter on the circuit, its input resistance should be as low as possible. This ensures that the ammeter does not significantly alter the circuit being measured.
For example, if the ammeter has a high input resistance, it would draw a significant amount of current from the circuit when connected in parallel. This would lead to a distorted measurement of the current, as some of the current would be diverted through the ammeter rather than flowing through the load.