Electric Circuits Legacy Problem #19 Guided Solution

One of the habits of an effective problem solver is to read the problem carefully and identify the known and the unknown information. This identification of the known information is usually written down and expressed in terms of variables or symbols which are used in the physics formulas pertaining to the topic. Here as we read this problem we read of a device that operates at 1500W on a 110V circuit and what I need to do is figure out what 1500W is in terms of the symbols of my physics formulas. Now the W represents watts and watts is a unit of power. So I could write down P equal 1500W and I have a power. The 110V is a little bit more obvious. That's a voltage drop across your electric toaster. I write down delta V equal 110V with the V in the statement being the unit in volts. Now what I'm looking for is the R, the resistance of this toaster oven. So I go to my list of physics formulas for the topic and find those if I click on the overview and link to the overview page for this set of problems. I'm looking for one that relates the P, the delta V and the R and indeed there is such an equation. It goes P equal delta V squared over R. Rearranging it so that I can solve for R, I'd have R equal delta V squared over P. Now I can substitute my two values into this equation, carefully to square the delta V and I'll get my answer right. It comes out to be about 8.06 repeating. I can round that to two significant digits and that's where the 8.1 ohms comes from.