Incoming links: Capacitor
The fundamental intuition about capacitors is that they never let electrons through.
They can only absorb electrons up to a certain point, but then the pushback becomes too strong, and current stops.
Therefore, they cannot conduct direct current long term.
For alternating current however, things are different, because in alternating current, electrons are just jiggling back and forward a little bit around a center point. So you can send alternating current power across a capacitor.
The key equation that relates Voltage to electric current in the capacitor is:So if a voltage Heavyside step function is applied what happens is:More realistically, one may consider the behavior or the series RC circuit to see what happens without infinities when a capacitor is involved as in the step response of the series RC circuit.
- the capacitor fills up instantly with an infinite current
- the current then stops instantly
Finding capacitance with an oscilloscope by Jacob Watts (2020)
Source. Good experiment.Capacitors Explained by The Engineering Mindset
. Source. 2019.This notation is designed to be relatively easy to write. This is achieved by not drawing ultra complex ASCII art boxes of every component. It would be slightly more readable if we did that, but prioritizing the writer here.
Two wires are only joined if but the following are:
+ is given. E.g. the following two wires are not joined: |
--|--
| |
--+--
|Simple symmetric components:
-,+and|: wireAC: AC source. Parameters:e.g.:Hz: frequencyV: peak voltage
If only one side is given, the other is assumed to be at a groundAC_1Hz_2VG.C: capacitorG: ground. Often used together withDC, e.g.:means applying a voltage of 10 V across a 10 Ohm resistor, which would lead to a current of 1 ADC_10---R_10---GL: inductorMICROPHONE. As a multi-letter symmetric component, you can connect the two wires anywhere, e.g.or:---MICROPHONE---| MICROPHONE |SPEAKERR: resistorSQUID: SQUID deviceX: Josephson junction
Asymmetric components have multiple letters indicating different ports. The capital letter indicates the device, and lower case letters the ports. The wires then go into the ports:
D: diodeSample usage in a circuit:a: anode (where electrons can come in from)c: cathode
Can also be used vertically like aany other circuit:--aDc--We can also change the port order, the device is still the same due to capital| a D c |D:--cDa-- | Dac-- | Dca-- | --caDDCDC source. Ports:E.g. a 10 V source with a 10 Ohm resistor would be:p: positiven: negative
If only one side is given, the other is assumed to be at a the ground+---pDC_10_n---+ | | +----R_10------+G. We can also omitpandmin that case and assume thatpis the one used, e.g. the above would be equivalent to:If the voltage is not given, it is assumed to be a potentiometer.DC_10---R_10---GT: transistor. The ports aresgTd:Sample usage in a circuit:s: sourceg: gated: gate
All the following are also equivalent:---+ | --sgTd--| g --sTd-- | --Tsgd-- |I: electric current source. Ports:s: electron sourced: electron destination
V: Voltmeter. Ports:If we don't need to specify explicit positive and negative sides, we can just use:p: positiven: negative
without any ports. This is notably often the case for AC circuits.---V---Optionaly, we can also add the sides as in:
Numbers characterizing components are put just next to each component with an underscore. When there is only one parameter, standard units are assumed, e.g.:means:Micro is denoted as
+-----+
| |
C_1p R_2k
| |
+-----+- a capacitor with 1 pico Faraday
- a resistor with 2 k Ohms
u.Wires can just freely come in and out of specs of a component, they are then just connected to the component, e.g.:means applying a voltage of 10 V across a 10 Ohm resistor, which would lead to a current of 1 A
DC_10---R_10---GWhen Ciro Santilli was studying electronics at the University of São Paulo, the courses, which were heavily inspired from the USA 50's were obsessed by this one! Thinking about it, it is kind of a cool thing though.
That Wikipedia page is the epitome of Wikipedia failure to explain things in a way that is of any interest to any learner. Video 1. "Tutorial on LC resonant circuits by w2aew (2012)" is the opposite.
Tutorial on LC resonant circuits by w2aew (2012)
Source. - youtu.be/hqhV50852jA?t=239 series LC circuit on a breadboard driven by an AC source. Shows behaviour on oscilloscope as source frequency is modified. We clearly see voltage going to zero at resonance. This is why thie circuit can be seen as a filter.
- youtu.be/hqhV50852jA?t=489 shows the parallel LC circuit. We clearly see current reaching a maximum on resonance.
LC circuit dampened oscillations on an oscilloscope by Queuerious Guy (2014)
Source. Finally a video that shows the oscillations without a driving AC source. The dude just move wires around on his breadboard manually, first charging the capacitor and then closing the LC circuit, and is able to see damped oscillations on the oscilloscope.Introduction to LC Oscillators by USAF (1974)
Source. - youtu.be/W31CCN_ZF34?t=740 mentions that LC circuit formation is the root cause for Audio feedback with a quick demo. Not very scientific, but cool.
LC circuit by Eugene Khutoryansky (2016)
Source. Exactly what you would expect from an Eugene Khutoryansky video. The key insight is that the inductor resists to changes in current. So when current is zero, it slows down the current. And when current is high, it tries to keep it going, which recharges the other side of the capacitor.Used e.g. in the Sycamore processor.
The most basic type of transmon is in Ciro's ASCII art circuit diagram notation, an LC circuit e.g. as mentioned at youtu.be/cb_f9KpYipk?t=180 from Video "The transmon qubit by Leo Di Carlo (2018)":
+----------+
| Island 1 |
+----------+
| |
X C
| |
+----------+
| Island 2 |
+----------+youtu.be/eZJjQGu85Ps?t=2443 from Video "Superconducting Qubits I Part 1 by Zlatko Minev (2020)" describes a (possibly simplified) physical model of it, as two superconducting metal islands linked up by a Josephson junction marked as The circuit is then analogous to a LC circuit, with the islands being the capacitor. The Josephson junction functions as a non-linear inductor.
X in the diagram as per-Ciro's ASCII art circuit diagram notation:+-------+ +-------+
| | | |
| Q_1() |---X---| Q_2() |
| | | |
+-------+ +-------+Others define it with a SQUID device instead: youtu.be/cb_f9KpYipk?t=328 from Video "The transmon qubit by Leo Di Carlo (2018)". He mentions that this allows tuning the inductive element without creating a new device.
The superconducting transmon qubit as a microwave resonator by Daniel Sank (2021)
Source.