EEVblog 1469 - AC Basics Tutorial - Part 2 - Phasors

Part 2 of the AC Basics tutorial series. What are phasors and doing phasor addition. In-phase, out of phase, and leading and lagging waveforms.
Phi vs Theta phase angle.
Leading into complex numbers in Part 3.

00:00 - AC Basics Theory
00:40 - How an AC waveform is produced
01:37 - Degrees, Radians and Gradians
02:30 - The ugly equation for AC voltage
03:08 - Theta vs Phi
03:51 - AC Ohms Laws, vectors, and impedance
04:42 - Phasors
05:24 - Two AC waveforms and phasor analysis
07:20 - Out of phase signals
08:50 - Phase shift
09:48 - Two sine waves always make another sine wave
10:22 - Angular frequency
11:45 - Phasor diagram
13:04 - How to add two phasors graphically
16:56 - CIVIL: Capacitors and Inductors with current Leading and Lagging
18:19 - Leading into Complex Numbers

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#ElectronicsCreators #Tutorial #AC

[thegreenxeno]

Your tutorial on Op Amps was essential to me helping my friend graduate an electrical technician program. These are great!

[karlm]

I needed this about 8 years ago when i was doing electrical tech in my ee degree. Confused the heck out of me at the time. Thank you!

[thosewhowishb]

I need to point out the convention for the sign of the angle.
In AC, φ is positive (anti-clockwise) for inductive loads (current lagging the voltage), and φ is negative (clockwise) for capacitive loads (current leading the voltage).
To accomodate the convention, the equation actually becomes v(t) = Vp*sin(ω*t - φ).
In your drawing, as you said, V2 is leading V1. While your phasor diagram checks out with the equation on the white board (summing φ inside the sin()), convention-wise, V2 is lagging V1 on the phasor diagram. The phasors should be reflected about the horizontal axis, or V2 should lag V1 on the plot against time.
This distinction is very important when designing power factor correction, single-phase machines, and the likes.

Btw, great video!

[martinda]

Ha, ha brilliant Dave. I admit, I almost didn't watch, but thought I may as well look through to see how you were doing. Well I'm glad I did because your 1/10th of a Smoot had me in stitches.

The community just couldn't be any luckier, to have such a wonderful ambassador.
I've thought about doing a first principles series...Just thought about it. Done nothing! Dave does it and keeps on giving. His energy and generosity are legendary as far as I'm concerned.

[BenChilds]

Well explained, Dave. In less than 7 minutes I now understand how the analog video vector-scope I used in college to color calibrate NTSC video decks to cameras works. I never could figure out why the target locations were at different distances from the center of the scope - it appears it's because it's showing the amplitude and the phase simultaneously.

[mastershifu]

Great work Dave. It comes both as a refresher and a lession for me! Thank you so much for starting this series 🙌

[keithminchin]

Dave this is awesome. I’ve been scratching my head for a while looking at some brushless motor control theory. Always a fan of the way you explain things.

[IanScottJohnston]

that takes me back many for refreshing my brain Dave!

[MattHollands]

Just to be completely specific about what you said at 15:20, any two sinusoidal waveforms *of the same frequency* that are added together will you give you another sinusoidal waveform.

[radman]

THANK YOU for producing this technical content, Dave. If you don't get hundreds of immediate viewers, consider it invaluable for the archives for students to refer back to when they need to visit this particular topic. Don't change a thing man!

[scottholmes]

Great video. No mucking about, just good ole fashioned physics. You could easily explain power factor with this video, and magnetic theory.

[ctigu]

One of the best explanations of this that I've seen. Thanks

[Sahko]

Great video! I would also love to see a video on how these phasors and the complex numbers relate and can be used to calculate inductance and capacitance values!

[fg]

Great video, as always! I want to point out that a lot of this is only true if the sine wave have the same frequency though. If the frequencies are different, then the sum of two sine is not a sine. In that case, phasor are not too useful (but complex numbers still work of course).

[kratz]

I'm saving this to watch later. As a comp sci major that took an AC analysis course from the physics dept. ('cause I thought it'd be fun), I'm excited to try and remember how in the hell I passed that class.

[gregorymccoy]

Ah the memories. These were always the busiest looking graphs in the textbooks. First time I saw them my jaw dropped. Turned out it was pretty simple 😀.

[Kombivar]

Great stuff, I had it earlier in course, now on the 3-phase systems, would be great to see the simpler explanation of star and delta connections.
All the best!

[TheZanger]

You probably didn’t expect this but this is also very interesting for audio engineers to better understand phase. Say you have to mic’s picking up one instrument, one close and one a bit further away and things start sounding funny. Or with peaks and dips in certain frequencies with speaker placement and room reflections. A lot of audio engineers struggle with understanding this when they start. Great explanation!

[janeklof]

Extremely good explanation - very pedagogic ! Many thousand thanks for your honesty and piece of excellent work ! You have a great knowledge and experience of electronics. It is nice to learn from a person who knows what he is talking about !

[IGobzter]

Lovely explanation Dave! It really helps after most of my university class got whopped on our first math exam of 2. semester, it was hard to grasp phasors based on our book.