help with some simple circuit problems please...

[Semidevil]

now, I think I could do it myself, but I just dont really understand the problem that well. Here's is what I got:


here is a simple circuit.
This is just a very simple box with

total Voltage = 21.21rms
R1 = 1.0 k ohms, and 5.65rms
R2 = 5 rms
R3 = ???
R4 = 560 ohms...

I need to find rms for R3. I know that by law, the sum of the R's is equal to the total voltage. But how do I calculate R3 when I don't have R4? I know that R4 has 560 ohms...is there a way to use ohms to find out how much rms R4 has??

here is a really simple one that I just can't think for some reason

A sine wave has frequencey of 50khz...how many cycles does it complete in 10 ms??

so 50khz is 5000 hz
10ms is .1 second...

divide and you get a big number.....

I dont' know.....can't think..........too much calculus,....can't do simple math

 

[thedarkwolf]

Are they all in series?

If they are its pretty simple. You know R1's resistance and how much voltage is across it so then you can figure out how much current there is in the circuit. Then you take the current and figure out how much voltage is across R4. Then you subtract the R1,R2, and R4's voltages from 21.21 and thats how much voltage is across R3. Now you know R3's voltage drop and current so you can figure out its resistance.

I have to know how its layed out if they all arn't in series.

As for the other one if I am thinking straight its 50,000hz and .1 sec is 1/10 of a sec so.......

Opps looks like I threw a few more things in there than you actually need but you should be able to figure out what I mean aslong as you know ohms law.

 

[OZEE]

First ... 10 ms <> .1s, it is .01s. 50khz is 50,000 cycles per second (NOT 5000). Move the decimal two places left >> 500 cycles in 10 ms.

And darkwolf is right ... for those resistors to make any sense, we've got to know the circuit ... all series, all parallel, mixed??? If it's all series, you've got enough information. If it's series, they all have the same current through them. You can get that by calculations based on the info given for R1. Then apply that current to R2 to get its resistance. You've then got it reduced to a single unknown resistor (R3) with known voltage drop and known current. Simple Ohm's Law problem, then.

If they're parallel, you've got the same voltage drop across each, but the current changes ... so you don't have enough info for that...

If it's mixed series/parallel, well, there's not anywhere's close to enough info to solve that...