I did an RL circuit experiment. It is a series circuit with a potentiometer, inductor, and a DC source.
Here is the resulting waveform at 2 different resistances (ch 1 is source voltage and ch 2 is voltage across the inductor.)
Why does the voltage across inductor on the first picture have 'jumps' and why does it curve like that in the second picture?
I am also confused as to why the source voltage is affected on the second picture.
It might help to think of a voltage divider plus the nature of a coil charging and discharging to help understand this.
In the first image the resistor is a very high value. This means that there is a large voltage drop across it so V2 is very low when V1 is high. The spikes you see on the edges of the pulse are due to the small amount of magnetic field collapsing and generating a spike of current on both rising and falling edges as the inductor stores current on BOTH rising and falling edges (it just flows the opposite direction as the field collapses, hence the negative and positive voltage increases). The large voltage drop is also why V2 looks almost zero: it is effectively at ground during steady state when the inductor is a short when charged with magnetic field (whereas capictors act as an open circuit when charged).
In the second image, the resistance is lower so more current is entering the inductor. When V1 switches, you are seeing the current flow out of the inductor and decay back down to Vhigh and Vlow just like in the first picture, but the current is so much higher that the exponential decay curve lasts longer and makes that nice curve. Since the resistor is so low, V2 is close V1 when high, however the current across R1 is much higher with the boost from the inductor, and that is read by BOTH voltage probes. It is likely that the voltage scales are different in the first image which is why you do not see spikes on the V1 probe.
Regarding the RL circuit: Notice the spikes in the inductor voltage are aligned with the rise/fall times of the source voltage. With inductor voltage equal to L(di/dt), we can conclude there is a substantial di/dt from the rapid dv/dt of the input source voltage during the brief rise/fall intervals, causing these briefs periods of substantial positive/negative voltage across the inductor. Also note that the voltage remains slightly positive after the spike for positive input voltage (likewise, slightly negative after the spike for negative input voltage). We can credit this to the ESR of the inductor, which has a voltage drop from the current in the circuit.
Regarding the RC circuit: This unfortunately appears to defy our expectation, given what we know of the circuit from your question. We expect an exponential charge of the capacitor voltage of the form:
vc(t) = Vsource*(1-exp(t/RC))
which occurs after each inversion of the source voltage polarity (see image below). This time to charge ought to increase when you increase the resistance of the pot. You may consider making a second attempt at this test and check for any errors. Best of luck!
You can intuitively understand this inductive circuit if you think of the inductor as of a "recheargable current source". Its operation is considered in five steps in the picture below which is a snapshot of a Flash movie (I cannot put a link to it because StackExchange policy does not allow it).
