Question

why is wheatstone bridge method considered unsuitable for the measurement of very high resistance?

Answer 1

We know that during a null condition the current carried by a galvanometer would be zero however a small amount of current would flow in the heavy resistor, this would cause galvanometer to defect and give a full scale reading. Thus, the sensitivity of the galvanometer would be compromised using a high resistance and thus the bridge becomes unsuitable under such conditions.