A fuse made of lead wire has an area of cross-section `0.2mm^(2)`. On short circuiting. The current in the fuse wire reaches 30A. How long after the short circulting will the fuse begin to melt? For lead, specific heat `0.032 "cal" g^(-1) .^(@)C^(-1)`, melting point `=327^(@)C`, density =`11.34g cm^(-3)` and the resistivity `=22xx10^(-6)Omega`cm. Initial temperature of the wire is `20^(@)C`. Neglect heat losses.