CBSE Class 10 Science 2018 · Paper 31/1/C · Question 21

(a) Magnetic field lines are the curves along which a free north pole (the north pole of a small compass) would move in a magnetic field; iron filings arrange themselves along them around a magnet. They are closed curves, running from N to S outside a magnet and from S to N inside it, and they never cross. The direction of the magnetic field at a point is given by the tangent to the field line at that point, in the sense of the arrow on the line; a compass needle placed there points its north pole along this direction. (b) Yes. The magnetic field of coil X passes through coil Y. When the current in X is changed, its magnetic field changes, so the magnetic field linked with Y changes, and this change induces a current in Y, whose ends are joined in a closed circuit, for example through a galvanometer (electromagnetic induction). The induced current lasts only while the current in X is changing. (c) Fleming's right-hand rule: stretch the thumb, forefinger and middle finger of the right hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the thumb in the direction of motion of the conductor, then the middle finger gives the direction of the induced current.