Question

7. Two light bulbs with ratings of 40 W and 100 W are plugged into sockets supplying 110 V. A) Calculate the resistance of each. Which has more resistance? The more resistance. (Notice that voltage is fixed) W bulb has B) If the 100 W bulb is operated continuously for 2 full days and electric energy costs $0.12 per kWh, how much does it cost? Convert W to kW multiply by the number of hours to get kW.h multiply by cost/k W.h Current cost- he volt 8. An aluminum wire carrying a current of 5 A has a cross sectional area of 4 x 106 m2. Find the drift speed of the electrons in the wire. The density of aluminum is 2.7 g/cm3. (Assume three electrons are supplied by each atom). e pro es, wi a) Recall the mass flow rate equation from semester 1 . Rmassflow VA b) Write the equivalent current relation for charges in a wire, 1- c) What is the electrical analogy with fluid density, ρ? d) Given that the molar mass of aluminum is M-27 g/mol and the density of aluminum is e Varit A p-2.7 g/cm3, determine the number of mol/cm3 for aluminum. p/M- e) Convert into atoms/m3, N/V -p/M (mol/cm) (10 cm/m3) (6.02E23 atoms/mol) - mol/cm3 ar atoms/m u: f) Convert into conduction electrons/m3 using the fact that each aluminum atom contributes 3 conducting electrons. n 3(electrons/atom) xN/V (atoms/m3) electrons/m C/m3 g) Get the charge density, nq h) Solve the equation in b) for the drift velocity, Vdnit i) Plug in the numbers to get Vdrift m/s Sec j) How long would it take an electron to drift 1

Answer 1