(i) Steel is used as a magnetic core in a transformer, it acts as a good conductor and whenever a tine varying flux pass through the core circulating currents are produced and known as 'Eddy currents' (ii) To reduce conductivity (Eddy current losses) by not destroying magneting properties, about 4 to 5% of silica impurity is added so that the conductivity of steel decreases. (iii) The high content of silica is not preferred the material becomes more brittle and it will destroy the mechanical properties.