1. The problem statement, all variables and given/known data An office worker uses an immersion heater to warm 250 g of water in a light, covered, insulated cup from 20 degrees C to 100 degrees C in 4 minutes. The heater is Nichrome resistance wire connected to 120V power supply. Assume wire is at 100 degree C during 4 minute time interval. a) calculate average power required to warm the water to 100 degree C in 4 min b) calculate the required resistance in the heating element at 100 degree C c) calculate the resistance of the heating element at 20 degree C d) derive a relationship between the diameter of the wire, resistivity at 20 degree C, rou (po), the resistance at 20 degree C, Ro, and the length L e) If L = 3 m, what is the diameter of the wire? What we are given: mass of water = 250 g density of water = 1000 kg / m^3 change in T = 80 V = 120V t = 4 minutes p of Nichrome = 150 *10^-8 coeff of resistivity of Nichrome = 0.4 * 10^-3 2. Relevant equations P = I*V = V^2/I = I^2*R R = V/I R = Ro [1 + coefficient of resistivity (T - To)] R = p L / A I = Q / t 3. The attempt at a solution a) calculate average power required to warm the water to 100 degree C in 4 min density = m / v ... v = m / density v = A * L v = 250 / 1000 = .25 m ^3 = A * L R = p L / (.25/L) = p L^2 / .25 How do I calculate I for Power without knowing the charge?