An electric iron of resistance 20 Q. takes a current f 5 A. The heat developed in joules in 30s is

The heat developed in an electric iron can be calculated using Joule's Law of Heating, which states that the heat produced (H) is directly proportional to the square of the current (I), the resistance (R), and the time (t) for which the current flows [2]. The mathematical formula is H = I²Rt [t2]. Given the current I = 5 A, resistance R = 20 Ω, and time t = 30 s, the calculation is H = (5)² × 20 × 30 [t2][t6]. This results in H = 25 × 20 × 30 = 15,000 Joules [t2][t9]. Since 1,000 Joules equals 1 kilojoule (kJ), the heat developed is 15 kJ. This principle is a standard application of the heating effect of electric current used in household appliances like electric irons and heaters [c2][t8].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > H = I2 > p. 189
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > 11.7 HEA 11.7 HEA11.7 HEATING EFFECT OF ELECTRIC CURRENT > p. 188