Question

Why should the resistance of:
(a) an ammeter be very small?
(b) a voltmeter be very large?

Answer 1

a) An ammeter is connected in series in the circuit. If its resistance is high, it will affect the current in the circuit and the reading won't be proper. So, an ammeter has a very low resistance.
b) A voltmeter is connected in parallel to the circuit. If its resistance is low, most of the current will be diverted through it, instead of the component across which the potential difference has to be measured. So, a voltmeter has a very high resistance.