Electric Circuits Audio Guided Solution EC7Q2

Problem Set EC7, Question 2:

A toaster is rated at 620 Watts when connected to a 120-V source. What is the resistance (in ohms) of the toaster?

Audio Guided Solution

A toaster is rated at 620 watts. When connected to a 120-volt source, what is the resistance of the toaster? So here we�re given the power, P equals 620 watts of a toaster, and we�re given the delta V. Delta V equals 120 volts of a toaster. We�re asked what is the resistance of this toaster. So we�re looking for the relationship between P, delta V, and R. And there�s a couple of ways you can go about this. One way you can go about finding the R is to use P and delta V and get the I. And then turn around and use the I along with the delta V in the Ohm�s law equation in order to get the R. So you would do P equal delta V times I, solve for I, and then you go delta V equal I times R, and solve for R. Another way is just combine the two equations together, and that�s been done for you likely in the classroom. And it�s also on the Set A overview page. You might want to kind of flip back and look at that. And what you�ll notice is it says P equal delta V squared over R. So do your substitution, your algebra, and solve for R, and you�ve got the same answer. Good luck to you.

Solution

Habits of an Effective Problem Solver

An effective problem solver by habit approaches a physics problem in a manner that reflects a collection of disciplined habits. An effective problem-solver...

... reads the problem carefully and develops a mental picture of the physical situation. If necessary, sketches a simple diagram of the physical situation to help you visualize it.
... identifies the known and unknown quantities and records them in an organized manner. Equates given values to the symbols used to represent the corresponding quantity - e.g., ΔV = 9.0 V; R = 0.025 Ω; I = ???.
... uses physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
... identifies the appropriate formula(s) to use.
... performs substitutions and algebraic manipulations in order to solve for the unknown quantity.

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