College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 20

An office worker uses an immersion heater to warm 250 g of water in a light, covered, insulated cup from 20°C to 100°C in 4.00 minutes. The heater is a Nichrome resistance wire connected to a 120-V power supply. Assume the wire is at 100°C throughout the 4.00-min time interval. (a) Calculate the average power required to warm the water to 100°C in 4.00 min. (b) Calculate the required resistance in the heating element at 100°C. (c) Calculate the resistance of the heating element at 20.0°C. (d) Derive a relationship between the diameter of the wire, the resistivity at 20.0°C, 0 , the resistance at 20.0°C, R 0 , and the length L. (e) If L = 3.00 m, what is the diameter of the wire