With the help of which law or rule can the direction of a magnetic field be known?

You have just paid the electricity bill for your house.
$(i)$ What was it that your family consumed,for which you had to pay?
$(ii)$ In what unit was it measured?

$(a)$ Describe an activity to show the pattern of magnetic field lines of a bar magnet,with the help of a cardboard piece and iron filings.
$(b)$ Compare the magnetic field of a bar magnet with that of a current-carrying solenoid with the help of a figure.

The magnetic field produced by a current in a straight wire has no poles.

What is short-circuiting?

$(a)$ What is the direction of magnetic field lines inside a bar magnet and outside of it?
$(b)$ What does the degree of closeness of the field lines represent?