Question

Why voltmeter have high resistance ? Why ammeter have low resistance ?

Answer 1

Voltmeter should not allow any follow of current through it for it to accurately measure the potential difference between two ends. That is why it should have a very high resistance.

Ammeter measures the amount of current passing through a given point in a conductor. Now, for it to accurately measure that, there should be no obstacles to current flow through it, thus it should have very less resistance.