The magnetic field at the centre of a current carrying circular loop of radius R is B₁. The magnetic field at a point on its axis at a distance R from the centre of the loop is B₂. Then the ratio (B₁ / B₂) is

The self-inductance of a solenoid of 600 turns is 108 mH. The self-inductance of a coil having 500 turns with the same length, the same radius and the same medium will be

The rms current in a circuit connected to a 50 Hz ac source is 15 A. The value of the current in the circuit $$\left( {{1 \over {600}}} \right)$$s after the instant the current is zero, is -

In a circuit the phase difference between the alternating current and the source voltage is $${\pi \over 2}$$. Which of the following cannot be the elements of the circuit?