Electronics Question...Impossible?

[Military Man]

Hi

Just a quick question, is it impossible to find the supplky voltage and current of a circuit by only knowing the value of the three resistors and the voltage across one of them?

[mono]

In a word NO.

If the cct is parallel, then the voltage across one will be the same as the others = cct voltage, the reciprocal sum of the resistances can be used to calculate the total resistance and so the current.

If the cct is series then the resistance ratios will determine the voltage dropped across each resistor which will then give total resistance and from this the current can be determined.

Actually quite simple Ohms Law.

[Military Man]

i do not quite understand. I have three resistors R1, R2 And R3 of resistances 16 ohms, 8 ohms and 2 ohms, the voltage across R2 is 2V and i have to calculate the supply voltage and current, but i have treid many ways of doing it and cant, lol, can you possibly enlighten me n this a bit more, thank yuo very much for your help

[STC]

This must be a series circuit we're talking about. If it is, then the current is the same through all resistances in the circuit, therefore if you find the current through one of the resistors, you can find the voltage drops across each of the rest.

Once you have the voltages, simply add them to resolve the supply voltage.

In your example, the current through the circuit is 0.25 Amps (2/8).

The voltage across R1 is therefore 4 Volts (0.25 *16) and the voltage across R3 is 0.5 Volts (0.25*2).

The supply voltage for the circuit is 6.5 Volts (VR1+VR2+VR3).

The formulas I used are I=V/R and V=IR.

Kirchoff's Voltage law is the basis for the calculations. It states:

The sum of all voltage drops and rises in a closed loop equals zero.

So the voltage drops across the resistors must be equal and opposite to the supply voltage.

[mono]

If you are still having a little trouble getting your head round it here is a (frankly superb) site.

Online electrical course (http://www.sea.siemens.com/step/default.html)

Click on the introductory course - 'basics of electricity'

For me this is what the internet is for. And its free!!

[Military Man]

Thanks a lot, much appreciated