# Calculate RMS current?

[SOLVED] calculate RMS current!?

1. Homework Statement

The maximum potential difference across certain heavy-duty appliances is 240 V. Assume that the total resistance of an appliance is 190 ohms.
(a) Calculate the rms potential difference.
169.68V <--CORRECT

but for

(b) calculate the RMS current,

i have no idea what to do!?

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G01
Homework Helper
Gold Member

i did 240V * .707 (i got .707 from Vrms)

G01
Homework Helper
Gold Member
Ok. Here's a hint:

HINT: RMS voltages and RMS currents across a resistive load follow rules analogous to their DC counterparts. So, do you remember how DC voltage and current across a resistor are related?

Ok. Here's a hint:

HINT: RMS Voltages and RMS Currents across a resistive load follow rules analogous to their DC counterparts. So, do you remember how DC Voltage and Current across a resistor are related?
i really don't,
and honestly i guess for part A.

i dont know why im taking physics, but im stuck with it.
its not that i dont try...
i just dont understand :\

i know DC and AC have something to do with transformers

G01
Homework Helper
Gold Member
Then you should look up the answer if you do not remember. You must have done DC circuits if you are discussing AC concepts like these. I'm telling you that the RMS voltage and current values across a resistor follow the same laws that DC voltages and currents across a resistor follow.

The fact that you don't remember that law means that you should probably review your notes from previous classes or look it up in your book. I do not see how me just giving you the law helps you in your physics education in the long run.

I'll ask you again, just so you are clear on what your looking for:

What law relates the DC voltage across a resistor to the Current through it? The RMS Values you are working with also follow the same law.

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Then you should look up the answer if you do not remember. You must have done DC circuits if you are discussing AC concepts like these. I'm telling you that the RMS voltage and current values across a resistor follow the same laws that DC voltages and currents across a resistor follow.

The fact that you don't remember that law means that you should probably review your notes from previous classes or look it up in your book. I do not see how me just giving you the law helps you in the long run.

I'll ask you again, just so you are clear on what your looking for:

What law relates the DC voltage across a resistor to the Current through it? The RMS Values you are working with also follow the same law.
i didnt say i dont remember, because i never knew in the first place....but is it Ohm's law? V=IR?

G01
Homework Helper
Gold Member
It is indeed Ohm's law. Apparently you did know. You just didn't know you knew.

Now that you know that the RMS Values of voltage and resistance follow Ohm's law, can you find the RMS current from the information you have?

again, a guess..

so, if V=IR

then 169.68=I*190? =.89

i think?

G01
Homework Helper
Gold Member
That is correct. Good Job.

Just a word of advice for your future posts on PF. You may have a bad teacher, or you may just not be a physics person, but that does not mean that you deserve to be given solutions or methods to solve your problems more than anyone else here. Here, we try to help you figure out how to solve the problems. We do not solve them for you or just give you the method to get to the solution. You would learn nothing from that. Now, you solved this problem yourself with only a little guidance from me. You should feel good about that. Would you have felt as good, or learned anything if I just told you to use Ohm's Law?

That is correct. Good Job.

Just a word of advice for your future posts on PF. You may have a bad teacher, or you may just not be a physics person, but that does not mean that you deserve to be given solutions or methods to solve your problems more than anyone else here. Here, we try to help you figure out how to solve the problems. We do not solve them for you or just give you the method to get to the solution. You would learn nothing from that. Now, you solved this problem yourself with only a little guidance from me. You should feel good about that. Would you have felt as good, or learned anything if I just told you to use Ohm's Law?
i understand thanks!