In an experiment where an electric motor is connected to a m

In an experiment where an electric motor is connected to a mechanical device, why is some electrical energy required even when there is NO mechanical work being done?

Solution

In the absence of mechanical load(or when machanical work done is zero), the motor needs electrical energy to account for its constant losses like hysteresis losses, eddy current losses, frictional losses and other mechanical losses. This concept is used to find the constant losses of a particular electric machine(even a transformer). In load test we measure the energy consumed which is nothing but the constant losses!