Recent content by arcnets2

Thank you marcusl and berkeman. There's the negative sign in many standard textbooks and even websites such as wikipedia, so I guess it's not a typo. Rather they treat the coil as a source. Still seems strange to me ...

marcusl, sorry, no offence meant! Just trying to understand. Well imagine you have L and R in series. You switch on the source. Then the current is I(t) = U/R (1 - exp (-R/L t)). OK? I can only derive this using U_ind = + L dI/dt, with a plus sign instead of minus. But the minus sign is...

I think it is definitely wrong. Yes marcusl, the field inside the coil opposes that in the source. But you could as well say that of a resistor. But I have never seen a minus sign in R = U/I.

Hi, Let L be an inductance, then you find the following formula in textbooks (high school level): U_ind = - L dI/dt When you actually do calculations for circuits, you see that the minus sign is wrong. So why do they put it there?

OK. But I think an inertial system is defined by a) actio = reactio holds b) Newton's Law holds. Isn't that equivalent to conservation of momentum?

Wow, that helps a lot. And you are fast. THANKS! :smile:

Hi all, at the risk of boring everybody, I have a question that has probably been asked before. We all know that Special Relativity is based upon the concept of invariant light speed. Let some light travel a distance s in time t, then (ct)^2 - s^2 = 0 should hold for any observer (in an...