Best experiments/demos for learning about capacitors and inductors

[mart1n]

As someone new to electronics, I'm trying to get a firm theoretical and practical grasp of capacitors & inductors and their applications.

Based on how I learn, I think it would be very helpful for me to setup and run various demos and experiments that show the various behaviors and characteristics of these components. For instance, I've read that capacitors basically act as resistors in AC circuits and the resistance value varies with frequency, I would like to setup a demo to see this in action.

I have a Rigol DS1054Z scope, DC bench top power supply and a Rigol DG1022Z function generator. What are some of the best experiments / demos I can setup and run to learn about capacitors and inductors?

Thanks to anyone who replies, I really appreciate it!

[rstofer]

Grab a 15 kOhm resistor and a 0.01 ufd capacitor and wire them in series with the other side of the capacitor connected to ground.  Insert a 1 kHz sine wave of some amplitude, say 1V, into the resistor (between the resistor and ground).  Connect Ch1 probe between the input and ground.  Connect Ch2 probe between the junction of the resistor/capacitor and ground.  Get things displaying on the screen and prove (using cursors and math) that the phase shift is very nearly 45 degrees.  Hint: Using properly placed cursors Bx-Ax about 125 us.  Why is that 45 degrees?  Note that 45 degrees is 1/8 of a cycle and 125 is 1/8 of 1 ms (1 kHz).  Calculate the capacitive reactance, draw the impedance vector diagram and calculate the theoretical phase shift.  What frequency gets exactly 45 degrees (measured and theoretical)?

http://keisan.casio.com/exec/system/1258032632

Same circuit, insert frequencies like 10 Hz, 100 Hz, 1000 Hz, 10,000 Hz and record capacitor voltage.  Determine -3 dB point for low pass filter.  You can use a DMM or get the values from your scope.  -3dB occurs when voltage at some higher frequency (like 1kHz) is 0.707 of applied voltage.

http://www.learningaboutelectronics.com/Articles/Low-pass-filter-calculator.php

http://www.aetechron.com/db_to_Voltage_Calculator_home.shtml

There's a reason that the -3dB point (corner frequency) turns out to have a 45 degree phase shift.

http://www.electronics-tutorials.ws/filter/filter_2.html  See the phase shift diagrams at "Frequency Response of..."

Same circuit, insert 500 Hz square wave and watch the rising and falling edges.  Calculate Tau (RC time constant) and prove that you have more than 6 Tau for both edges.   If you do have more than 6 Tau, what percent of the input voltage is stored on the capacitor after 6 Tau.  How high is the voltage in 1 Tau, 2, 3, 4 and 5 as a percentage.  Hint: voltage in 1 Tau is about 63%

http://mustcalculate.com/electronics/rctimeconstant.php?c=0.01u&r=15000  gives 150 microseconds.

150 microseconds times 6 gives about 1 millisecond so we allow 1 ms for charge and 1 ms for discharge, hence 500 Hz.

There's a bunch to learn with a simple resistor and capacitor.  Turns out I was building up these very experiments to show my grandson.  He is considering EE as his major.

You can make up the same sequence of experiments for an inductor.  Just pick a value that matches some resistor value and center frequency:

http://www.learningaboutelectronics.com/Articles/Low-pass-filter-calculator.php#answer2

The resistance of the inductor may not be insignificant.  You can include it as a resistor in series with the real resistor.

[Decoman]

As a side comment, I thought I'd just mentioned that one thing I've learned about science, is that experiments are particularly interesting because of how an accurate prediction of yours with regard to measurements will gain merit (being trustworthy) when you also find that the measured results closely matches your concrete prediction with math and formulas. This opposed to doing an experiment where you get to measure things, and then simply end up trying to interpret the results in a speculative way, however meaningful it might seem that way.

[tggzzz]

Just "doing experiments" is fine, but only up to a point.

Normally it is best to do experiments to prove something or other. In this case you should first get an understanding of how components work in theory, specifically including what their predicted impedance is as a function of frequency. Yes, you will need some maths; there are many introductory textbooks.

Then calculate what you would expect to see if your understanding is correct.

And only then start connecting components and equipment!

Since your equipment and connections are part of the experiment, you should estimate how their imperfections will affect the measured results. Ideally you will choose parameters that ensure there is no visible effect. In this case that will mean having resistances that are neither too high nor to low, and frequencies that are not too high.

[rstofer]

I have always learned by doing and not so much by reading.  I can read what is supposed to happen and maybe I get something out of it, maybe not.  But if I build it and watch it work, I will probably never forget it; it's called kinesthetic learning.  I need to touch and feel.

It's hard in a single forum post to cover all of the details of AC theory but with a little outside reading (links), those experiments cover a lot of ground.  We have:

• Capacitive Reactance
• Impedance Vectors
• Graphical Phase Shift
• Scope Measurements
• Measured Phase Shift
• Time Delay vs Angle
• Calculating Corner Frequency
• Bode' Plot (without calling it that)
• RC Time Constant
• Capacitor Charging/Discharging Without The Math
• Low Pass Filter (without calling it that)

There's certainly a lot more to learn but that's quite a list for 2 simple parts, a signal generator and a scope.  I probably could have added a link to the time constant bit:

http://www.electronics-tutorials.ws/rc/rc_1.html

OTOH, not everybody is up for exponential equations right out of the gate although the explanation is excellent.

The wonder of the Internet is the availability of tutorials - there was no such thing back in the early '70s and textbooks tended to be dry tomes full of math.  Things are so much better 45 years later.  Matlab versus slide rule; I know which one I'll pick!

[Old Printer]

Rstofer, thanks for laying this out. I am going to crank up my AD2 and run through the stages. After a year of reading I am getting a basic feel of EE though I have dabbled all my life, just turned 65. I am week in math and working out experiments help me verify what equations tell me.

[tggzzz]

The wonder of the Internet is the availability of tutorials - there was no such thing back in the early '70s and textbooks tended to be dry tomes full of math.  Things are so much better 45 years later. 

When I was growing up the books split into two very distinct categories:

• recipe books or witchcraft books, which gave monkey-see-monkey-do instructions, but few hints about how something worked and why something worked. I've just been looking at my (1923?) book on how to make a radio (and XRay machine!), and it exemplifies the sheer frustration of such "practical" books. Example: to make a condensor, cut zinc sheets as shown in figure 1, and put presspahn in between the sheets. (No mention of what presspahn was, or why it was necessary!)
• textbooks which were full of equations that were difficult to translate into a working circuit

There were exceptions, but they were few and far between - e.g. "Wireless World" magazine bridged the gap.

Then "The Art of Electronics" arrived, to everybody's delight and relief.

[rstofer]

Rstofer, thanks for laying this out. I am going to crank up my AD2 and run through the stages. After a year of reading I am getting a basic feel of EE though I have dabbled all my life, just turned 65. I am week in math and working out experiments help me verify what equations tell me.

I'm a wee bit older, just turned 72.  I'm convinced that it is possible to keep right on learning.

If you want to get further into the math, I'm would recommend Matlab and the book "Solving DC and AC Circuits By Example Using Matlab".  I might even recommend it as a textbook instead of just a side issue.  There's a lot of discussion about the theory.

Matlab Home Edition is about $149 plus $45 for each toolbox add-on.  I have the Simulink add-on and it is really a nice tool.

https://www.mathworks.com/store/link/products/home/new?s_iid=htb_buy_gtwy_cta4

There are other tools like wxMaxima, Octave, Maple, Microsoft Mathematics and, of course, the scientific calculator.  I use an HP 48 GX that is always right in front of me.  It is probably more important to find a good book before selecting a tool.

[paulca]

I found these great:


EG:




Also http://www.falstad.com/circuit/
Click on "Circuits" and start selecting things.  For example:  AC Circuits->Inductors.

[rhb]

Another suggestion.

Feed a square wave to a capacitor, inductor and resistor in series and look at the voltages across each.  Then fire up Octave and reproduce it mathematically.  Use the scope math functions to look at each of the voltage differences.  Change the component values and watch what happens.

Then use this information to build an LCR meter like the cheap units on eBay using an Arduino.

Have Fun!

[w2aew]

You  might enjoy some of my older videos on capacitors and inductors:

[Old Printer]

You  might enjoy some of my older videos on capacitors and inductors:

I will second this! I have watched many of Alan's excellent videos to the point of being able to quote them from memory. Cannot begin to tell you how much I have learned from him, most worthy of your time.

[rx8pilot]

Alan's w2aew videos are truly a gift to society. You not only learn the concepts, you also see the practical reality and how to measure it.

[IanMacdonald]

Capacitors don't like changes in the voltage across them and will induce currents which tend to oppose such changes.

Inductors don't like changes in the current flowing through them and will induce voltages which tend to oppose such changes.

Put a capacitor and inductor in parallel, apply a pulse, and a 'conflict of interests' will develop as one tries to prevent the voltage changing, the other to prevent the current from changing. The result is that the energy is continually shunted back and forth between them. 

The one that's harder to grasp is the series resonant circuit, but if you look at it as a parallel circuit with a break in it where a current is injected, then its behaviour becomes plain.

[rstofer]

Alan's w2aew videos are truly a gift to society. You not only learn the concepts, you also see the practical reality and how to measure it.

Indeed they are!

Ham Radio isn't really my thing yet here I am buying a matching Grid Dip Meter so I can replicate his experiments with capacitors and inductors!  If I keep watching these videos, I might get a handle on this electronics stuff some day.

My grandson is considering EE as a major.  It's not locked in yet (and I will encourage him to take CS instead) but if he does, the eevBlog and w2aew channels are great resources.

[rhb]

Your grandson should do both EE and CS.  That will set him apart from the hordes of under qualified and over indebted graduates.  It's not as if you can escape computers these days no matter what field you go into.

[rstofer]

Your grandson should do both EE and CS.  That will set him apart from the hordes of under qualified and over indebted graduates.  It's not as if you can escape computers these days no matter what field you go into.

We're actually working in that direction.  He can certainly take CS electives within the EE curriculum.  In grad school, I took both and the university asked me which I wanted on my diploma - CS or EE.  I chose EE because, in 1976, CS wasn't the industry it is today.  We had your basic COBOL or FORTRAN programmers and little else.  I was a FORTRAN guy myself but I dabbled with COBOL.  Who knew they would still be in use 40 years later?

The only reason I recommend he consider CS over EE is that the Bureau of Labor Statistics has estimates of job growth and the outlook if pretty grim for EEs.  They project thousands and thousands of CS jobs.  It's pretty easy to get in when there are so many projected openings.

I wish I had hung around grad school instead of graduating.  There were a number of courses I would have liked to take.  I was young and I ate that stuff up!

Yup!   He'll have to go to grad school...