State one main difference between $AC$ and $DC$. Why is $AC$ preferred over $DC$ for long-range transmission of electric power? Name one source each of $DC$ and $AC$.

In domestic electrical wiring,what is the red-colored insulated wire used for?

$A$ current-carrying solenoid behaves like a bar magnet.

Describe in short an activity to:
$(i)$ demonstrate the pattern of magnetic field lines around a straight current-carrying conductor, and
$(ii)$ find the direction of the magnetic field produced for a given direction of current in the conductor. Name and state the rule to find the direction of the magnetic field associated with a current-carrying conductor. Apply this rule to determine the direction of the magnetic field inside and outside a current-carrying circular loop lying horizontally on a table. Assume that the current through the loop is anticlockwise.

What is the direction of magnetic field lines inside a bar magnet?

$(a)$ 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?