What is the frequency of $220 \ V$ $DC$ voltage? (In $Hz$)

Which rule is used to determine the direction of induced current in a circuit?

$(a)$ An electric current is passed in a horizontal copper wire from east to west. Explain your observations when a compass needle is placed $(i)$ below this wire,$(ii)$ above the wire. Draw inference from your observations.
$(b)$ List the factors on which the strength of the magnetic field due to a straight conductor carrying current depend. How should these be changed to decrease magnetic field at a point?

What is the shape of the magnetic field lines around a circular current-carrying conductor?

How is alternating current $(AC)$ different from direct current $(DC)$?

Explain with the help of a labelled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current-carrying coil has $n$ turns,the field produced at any point is $n$ times as large as that produced by a single turn?