Question

An electric iron of resistance 20 ohms take a current of 5 ampere calculate the heat developed in 30 second

Answer 1

according to joule's law of heating,
 H=I²RT
where I=current
           R=resistance
           T=time
therefore H=5²×20×30
                  =25×600
                  =15000 joules

Answer 2

Given :-

R = 20 Ω

I = 5 A

t = 30 s

H = I^2Rt

= (5)^2×20×30

= 15000 J

= 1.5 × 10^4 J