Question

Why ammeter has low resistance?

Answer 1

One of the reasons you want an ammeter to have low resistance is to prevent the ammeter from inducing IR voltage drops to the load where you are trying to measure it’s current. It comes down to simple Ohms law, so for example if you have a load that is working on 10 V you would not want that load to see anything less than 10V. In most cases you would want your ammeter resistance to be no more than 1% of the maximum load resistance so the accuracy of your current measurement is within 1%, Ideally you want your ammeter resistance to be less than 0.1% of what your load resistance is for precise measurements.

Answer 2

if ammeter has resistance it will use some current from the circuit and give wrong value of current . that is why the ammeter has almost negligible current so that it can not use any current and give correct result