1. The problem statement, all variables and given/known data The potential divider XZ has a potential of 3.0 V across it. When the contact is at the position Y, the resistance of XY equals the resistance of YZ which equals 12Ω. The resistance of the lamp is 4.0Ω. Picture of the relevant circuit: http://www.mediafire.com/view/w8te8yb3zwy4qiu/Screen%20Shot%202014-01-11%20at%207.46.44%20pm.png Heres a link - can't get the embed to work :/ http://www.mediafire.com/view/w8te8yb3zwy4qiu/Screen Shot 2014-01-11 at 7.46.44 pm.png 2. Relevant equations V=IR 1/R1 + 1/R2 = 1/RT R1 + R2 = RT 3. The attempt at a solution So far I've worked out the resistance across the lamp from: 1/4 + 1/12 = 3Ω, Then worked out the total resistance from: 3Ω + 12Ω = 15Ω. And then worked out the total current from: I=V/R = 3/15 =0.2A At this point I know that if I can find the current across the lamp, the pd across the lamp will be easy to find... but this is where I get confused. Thanks to whoever may answer!