A transformer which steps down $$330 \mathrm{~V}$$ to $$33 \mathrm{~V}$$ is to operate a device having impedance $$110 \Omega$$. The current drawn by the primary coil of the transformer is :
A cell of emf E and internal resistance r is connected to two external resistances $$\mathrm{R_1}$$ and $$\mathrm{R_2}$$ and a perfect ammeter. The current in the circuit is measured in four different situations:
(a) without any external resistance in the circuit.
(b) with resistance $$\mathrm{R_1}$$ only
(c) with $$\mathrm{R_1}$$ and $$\mathrm{R_2}$$ in series combination.
(d) with $$\mathrm{R_1}$$ and $$\mathrm{R_2}$$ in parallel combination.
The currents measured in the four cases in ascending order are
Select the unit of the coefficient of mutual induction from the following.
Steel is preferred to soft iron for making permanent magnets because,