21. An electric iron of resistance 20Ω takes a current of 5 A. Calculate the heat developed in 30 s.

Given, Electric current (I) = 5A, Resistance (R) = 20Ω, Time (t) = 30s
Heat developed, H = \(I^2 R t\) = 25 x 20 x 30 = 15,000 J \)

We have, H = \(1.5 x 10^4 J \)