State Joule's law of heating and give its mathematical form. An electric iron takes a current of 5A and develops `1.5 xx 10^(4) J` of heat energy in 30 s. Calculate the resistance of the electric iron.

Explanation

Mathematical form of Joules' Law of Heating is, `H = I^(2) R t`
`I = 5A, H = 1.5 xx 10^(4) J, t = 30` seconds, R = ?
`R = (H)/(I^(2) xx t) = (1.5 xx 10^(4))/(5 xx 5 xx 30) rArr R = (0.06 xx 10^(4))/(3 xx 10) = 0.02 xx 10^(3) Omega`