Measuring lag / lead on a scope

[j.a.mcguire]

Slightly hesitant to ask this for fear of being ostracised as I'm sure the answer is relatively straight forward.  I was watching the following youtube video:



Where around the 3:30 mark the chap is talking about the effect of inductance to cause current / voltage lag.  What I'm interested in is how he was able to connect the scope to simultaneously view the current / voltage for lag and lead?

Voltage is easy enough, stick your probe onto the secondary output.  But how does one measure current using a scope, since you can't put the scope in line?

I suspect a clamp meter / toroid would be the correct method but how is it possible to calibrate the scope to display these readings accurately? Plus the problem as I see it here is the inherent inductance of the clamp meter itself.

[Simon]

Always remember, no question is too silly to ask. I've not watched the video but a series resistor can be used as a current sense. Although you have to be careful needing a parallel and series connection as you can find your ground shorting. Other devices could work of course.

[w2aew]

It appears that he is measuring the voltage across the series combination of an inductor, LED and resistor, and then also measuring the voltage just across the resistor.  The latter will be proportional to the current.

I have a video that describes the voltage and current flow through capacitors and inductors, started with pen & paper, then followed up by some scope measurements: