ABSTRACT
Cell can be divided into two kinds: primary cells and Secondary cells. In these the cell is assembled and is immediately capable of supplying electricity as a result of chemical reactions. The electrical resistance of most substances increases with temperature, so if the small lamp is glowing brightly its resistance will be much higher than when there is insufficient current to make it light up. With the exception of a few items such as pocket torches almost all electrical devices are 'fused'-that is they contain somewhere a small component consisting of a length, perhaps a centimetre or two, of special wire designed to melt when the current flowing in it exceeds a certain value. The magnet is of the 'horseshoe' type and the poles are specially shaped with a cylindrical core of magnetic material. This concentrates the flux and also helps to make the flux density reasonably constant over the region in which the coil moves.
