A coil offers a resistance of $$20 \mathrm{~ohm}$$ for a direct current. If we send an alternating current through the same coil, the resistance offered by the coil to the alternating current will be :
A square shaped aluminium coin weighs $$0.75 \mathrm{~g}$$ and its diagonal measures $$14 \mathrm{~mm}$$. It has equal amounts of positive and negative charges. Suppose those equal charges were concentrated in two charges $$(+Q$$ and $$-Q)$$ that are separated by a distance equal to the side of the coin, the dipole moment of the dipole is
If the earth has a mass nine times and radius four times that of planet X, the ratio of the maximum speed required by a rocket to pull out of the gravitational force of planet $$\mathrm{X}$$ to that of the earth is
Two similar coils $A$ and $B$ of radius '$$r$$' and number of turns '$$N$$' each are placed concentrically with their planes perpendicular to each other. If I and $$2 \mathrm{I}$$ are the respective currents passing through the coils then the net magnetic induction at the centre of the coils will be: