What is the time derivative of resistance? Is there a unit for $\frac{\Omega}{sec}$? I have tried looking it up, but I can’t find anything
 A: Contrary to what the other answers say, resistors do change their value with time, even the most accurate ones, even at perfectly constant temperature. This is due to various phenomena, e.g. release of internal stresses, contamination from impurities etc. For instance, National Metrology Institutes keep historical records of the drift of their standard resistors, which is typically quite predictable and can be used to interpolate resistance values between calibrations.
The resistance drift of a resistor is usually specified in relative terms, that is, by the relative drift coefficient
$d = \dfrac{1}{R}\dfrac{\mathrm{d} R}{\mathrm{d} t},$
the SI unit of which is $\mathrm{s}^{-1}$. When the drift coefficient is constant, you can predict the value of the resistance $R(t)$ at time $t$ from its value at time $t_0$, with the equation
$R(t) = R(t_0)[1+d(t-t_0)].$
It is also worth noting that the unit $\Omega/\mathrm{s}$, which you mentioned in your question, really is an SI unit, it's just a unit without a special name (e.g. farad, symbol F, is just a special name for $\mathrm{s}^4\mathrm{A}^2\mathrm{m}^{−2}\mathrm{kg}^{−1}$).
A: Resistors are usually a constant value. They may vary with temperature but you'd need to know the material the resistor is composed of. If you just search on resistors you should be able to find technical sheets for different resistors that will have information as I described. The resistors should be constant in time so $d\Omega/dt$ = 0.
A: There is no SI unit for the time derivative of resistance. That is probably because resistance does not normally vary as a function of time.
