Physics 102 in-­‐class problems 7/10/14 Team Blue: 3 120W light bulbs are wired up such that two are in parallel and the third is in series with these. If one of the parallel ones burns out, do the others get brighter or dimmer? What fraction more / less light (total) comes out? Hint: The light that comes out is proportional to the electrical power dissipated in a bulb. A burned-­‐out bulb’s filament (wire) is broken so no current can flow. Team Green: In the drawings below, resistor A is 1 Ohm, resistor B is 10 Ohms and resistor C is 100 Ohms. In each case, which resistor heats up the most? Team Yellow: About 10% of the electrical power from an incandescent bulb comes out as visible light. a) What is the resistance of a 40W bulb (it takes 40W of electrical power when plugged into 120V). b) How much light do you get if two bulbs are wired in parallel? c) How much light do you get if they are wired in series? Team Purple: The ‘voltage divider’: Suppose you need 12V to run your coffee cup heater. You do it using a voltage divider as below (the funny symbol to the right is ‘ground’, which is taken to be 0V). The midpoint (VL) is connected to the heater (a.k.a ‘load’ or RL in the diagram). What is VL if RL = 1000Ω? 100Ω? 10Ω? What is the power dissipated in the heater in each case? Team Red: In the diagram below, how much current goes through the 200 Ohm resistor? How long will it take to deplete a 2 A-­‐hr battery? TEAM BLUE : KURTZMAN, FIELD, SANDERS, ENRIQUEZ TEAM RED : ZEB, OLT, DECLOUETTE, BERLAS TEAM GREEN : THOMAS, XI, QUINN, NEGA TEAM YELLOW: SERLETTI, KENNEDY, GODBE, KOTLOFF TEAM PURPLE: DEARING, PAUL, BELNAVIS