Reply To: Voltage Drop Equations

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Susan BrownSusan Brown

Hi Daniel,

Yes, if a circuit is drawn with L1 on one end and N on the other, then the voltage supply is 120vac. L1 on one end and L2 on the other means 240vac. So, it’s important to pay attention to what is written there.

That supply voltage will also be the total amount of voltage that is dropped across how ever many loads there are in the circuit, and each voltage drop will be proportional to the resistance of the load.

You wrote a circuit with L1 and N. Note – a lot of the questions in that quiz have L1-L2 – be sure you pay attention! šŸ™‚

Given the circuit you wrote above, then your calculation of current is correct. In a series circuit *current does not change*. It is the same at any point. So you calculate a total resistance for the circuit as you did in order to then calculate current according to I = E/R.

Now, for the power across the loads. The equation you chose uses voltage. But it has to be the voltage drop across that particular load – not the supply voltage as you used. So you can either calculate the voltage drop across each load, using the current that you already know, and then use an equation for P. (P = I x E would be easier at this point.) OR – you can do it in one step by using the equation P = I2 x R (using the R for each particular load). (There are often multiple ways to get to the correct answer using Ohm’s Law equations. That’s why it’s important to have a good feel for what you are actually doing, and not blindly “plug and chug”.)

Does that make sense? Be sure to follow up with more questions if you need to!