Answer: ( H = I^2 R t = 5^2 \times 20 \times 30 = 25 \times 20 \times 30 = 15000 , \text{J} ) In-Text Questions (Page 220) Q1. What determines the rate at which energy is delivered by a current? Answer: Electric power ( P = V \times I = I^2 R = V^2 / R )

Answer: Alloys have higher resistivity and do not oxidize easily at high temperatures.

Answer: Total R = 0.2+0.3+0.4+0.5+12 = 13.4 Ω ( I = 9 / 13.4 \approx 0.67 , \text{A} ) (same in series)

Answer: Charge on one electron ( e = 1.6 \times 10^{-19} , \text{C} ) Number of electrons in 1 C = ( \frac{1}{1.6 \times 10^{-19}} = 6.25 \times 10^{18} ) In-Text Questions (Page 202) Q1. Name a device that helps to maintain a potential difference across a conductor. Answer: A cell, battery, or power supply.