× → ind ( r, inwards) Figure . First illustration of Lenz’s law 12th - 12th - - - - - Unit ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT Figure . Second illustration of Lenz’s law No motion (b) G (c) G (a) G Repulsion between coil and magnet Attraction between coil and magnet current should flow in such a way that it opposes the movement of the north pole towards coil. It is possible if the end nearer to the magnet becomes north pole (Figure .
(b)). Then it repels the north pole of the with its plane perpendicular to the field. The arm AB is movable so that it can slide towards right or left. If the arm AB slides to our right side, the number of field lines (magnetic flux) passing through the frame ABCD increases and a current is induced.
As suggested by Lenz’s law, the induced current opposes this flux increase and it tries to reduce it by producing another magnetic field pointing outwards i.e., opposite to the existing magnetic field. The magnetic lines of this induced field are represented by red-colored circles in the Figure . (b). From the direction of the magnetic field thus produced, the direction of the induced current is found to be anti-clockwise by using right-hand thumb rule.
The leftward motion of arm AB decreases magnetic flux. The induced current, this time, produces a magnetic field in the inward direction ( red-colored crosses) i.e., in the direction of the existing magnetic field (Figure . (c)). Therefore, the flux decrease is opposed by the flow of induced current.
From this, it is found that induced current flows in clockwise direction. Illustration Let us move a bar magnet towards the solenoid, with its north pole pointing the solenoid (Figure . (b)). This motion increases the magnetic flux of the coil which in turn, induces an electric current.
Due to the flow of induced current, the coil becomes a magnetic dipole whose two magnetic poles are on either end of the coil. In this case, the cause producing the induced