Electricity - Plz Help!

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By considering a wire of radius 'r', lenght 'l' and resistivity 'e' through which a current I flows, show that

a) the rate of production of heat by it is I^2*P*l / pi*r^2

b) the rate of loss of heat from its surface is 2pi*r*t*h , where 'h' is the heat lost per unit area of surface per second.

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