Which resistor produces the most heat?

[epenguin]

If you mark up the drawing correctly and apply KVL you should get an equation like this..

+15 + 10 + 10 + ? = 0

where ? is the voltage across the current source. It's not going to be -15V.

PS...

KVL says the voltages around a loop sum to zero. I find I make far fewer errors if I always write an equation that explicitly adds up to zero (eg V1+V2+V3+V4 = 0) and avoid trying to guess the polarity and write something like V1 + V2 + V3 = -V4

Thx, I get it now. So e.g. going round the outside circuit from bottom left corner potentials are successively 0, -15, +20, +10. Over the current source current is in the direction of voltage increase not decrease.

But no one to say the resistance there is -35 Ω - if voltage across it changes, current is still 1 A. A non-ohmic element. (Nohmic? Gnomic?)

It just needs dropping a few mental habits leaned in circuits with constant voltage supplies.

 

[CWatters]

Thx, I get it now. So e.g. going round the outside circuit from bottom left corner potentials are successively 0, -15, +20, +10. Over the current source current is in the direction of voltage increase not decrease.

That's not what I get at all.

By bottom left corner I take it you mean the junction between the 20R and the 15R ?

You didn't say which way around you are going either and that changes the sign of all the voltages.

If you go clockwise you get +10 +10 -? +15 = 0 where ? is the voltage across the current source. Solve to give ? = -35V. As you are going clockwise that means the top end of the current source is +ve wrt the bottom.

If you go anti clockwise you get.. -15 + ? -10 -10 = 0. Solve to give ? = +35V. As you are going anti clockwise that means the top end of the current source is +ve wrt the bottom which is the same thing.

 

[epenguin]

We are in substatial agreement now, I was going anti-clockwise just as far as the junction where the voltage is + 10 V same as the potential from battery, I.e. two routes to same point where you do a circuit in one direction, perhaps preferable but equivalent.