(a) What are magnetic field lines ? How is the direction of magnetic field at a point in a magnetic field determined using field lines ?
(b) Two circular coils X and Y are placed close to each other. IF the current in the coil X is changed, will some current be induced in the coil Y ? Give reason.
(C) State " Fleming's right hand rule .

Explanation

(a) Megnetic field lines are the lines drawn in a magnetic field along which a north magnetic pole would move. Magnetic field line are also known as magneticf lines of force.
Direction of magnetic field lines is determined by the following activity.
A bar magnet is placed on a sheet of paper and its boundary is marked with a pencil. A magnetic composs is brought near the N-pole of the bar magnet. It is observed that N-pole of magnet repels the N-pole of compass needle due to which the tip of the compass needle moves aways from the N-pole .
Thus a magnetic field pattern is obtained around a bar magnet. Each magnetic field line is directed from the north pole of a magnet . the strength of magnetic field is indicated by the degree of closeness of the field lines. So the magnetic field is the strongest near the poles.

(b) Two circular coils X and Y are placed close to each other. If the current in coil X is changed, the mangnetic field associated with is also changes around the coil Y placed near it . This change in magnetic field induces a current in the coil Y.
When the current in coil X is switched on , it becomes an electromagnet and produces a magnetic field around coil X is switched off, its magnetic field in coil Y stops quickly. This effect is just the same as pulling a magnet quickly out of the coil Y , an induced current flows in coil Y in the oppsite direction.
(C) Fleming right hand rule . Hold the thumb, the forefinger and the centre finger of your hand at right angles to one another. Adjust your hand is such a way that forefinger pionts in the direction of magnetic field, and thumb points in the direction of motion of conductor, then the direction in which centre finger points gives the direction of induced current in the conductor.