Find the Value of Resistor R Please

[Andre36]

So Im hear doing some homework and I cannot figure how to find the value of resistance r in both of these diagrams. Can someone show me the formula pls. You can click to enlarge them.

Thanks.

Diagram 1




Diagram 2

 

[spikester]

Andre

For diagram 1 work out the parallel network resistance and using the 1A calculate the voltage across the network, take this voltage away from the supply and that is the voltage across r, then it is ohm law again to work out r.

For diagram 2 uses ohm's law for the 20 ohms and 0.5A then this voltage can by taken away from supply to work out voltage across 5 ohms. For the 5 ohms calculate I then take 0.5A away from it and you now have I and V across r, simple ohms law again to work out r.

Hope this helps.

 

[JorgeC]

Hi! people!
Spikester is right and had answered the question. We know the resistance value ( 20 ohm and is cross with 0,5A),so now using the law ohm we get the voltage applied at parallel resistance. knowing this value is easy to get the voltage on 5 ohm resistance and then the current.

Now the rest is easy!

 

[tony mc]

Just had another look and can see what I was missing and the position of the 0.5A. I took it as 0.5 A for the entire cct at first must use my Mr Magoo glasses more often !


Thanks