The core used in transformers are laminated to

The end correction for the vibrations of air column in a tube of circular cross-section will be more if the tube is

If the work done in blowing a soap bubble of volume ' V ' is ' W ', then the work done in blowing a soap bubble of volume ' 2 V ' will be

A coil has inductance H . The ratio of its reactance when it is connected first to an a.c. source and then to d.c. source is