What else have I (or others) forgotten.

brightspark

Not sure if I've reached the stage where every time I learn something new I forget something old, but I was reminded recently that there are some things I once knew that I should revise.

I had forgotten how to solve this



Find the current flowing in R2.

I knew Thevenin's theorem was involved, but not how to use it. 20 years ago I probably could have solved it in my head.

I obviously never needed it though during the last 20 years.

Does anyone have similar experiences?

tomdempsey200

brightspark wrote: »

Not sure if I've reached the stage where every time I learn something new I forget something old, but I was reminded recently that there are some things I once knew that I should revise.

I had forgotten how to solve this



Find the current flowing in R2.

I knew Thevenin's theorem was involved, but not how to use it. 20 years ago I probably could have solved it in my head.

I obviously never needed it though during the last 20 years.

Does anyone have similar experiences?

did electronics full-time for 2 years ...i've even forgot thevenin now

don't recall doing thevenizing at fas electrical..can't remember that either

2011

It has been a while....
Basically it is about working out the Thevenin's equivalent voltage and resistance.
The circuit can then be redrawn with a single voltage source and resistor in series with the load.
There is a good link on Wikipedia.

brightspark

2011 wrote: »

It has been a while....
Basically it is about working out the Thevenin's equivalent voltage and resistance.
The circuit can then be redrawn with a single voltage source and resistor in series with the load.
There is a good link on Wikipedia.

Yes, I googled Thevinin to find the method, easy enough to solve....when you remember it!

tomdempsey200

i spend a while practising conduit jumps on the bending machine for work there a while back

made a few nice jumps on 20mm drops on the install

i've forgot now how i did them..should have kept some paper notes

TimeToShine

If I were to take a chance I would just use KCL and label the middle node as x, so you have (28-x)/4 = x/2 + (x-7)/1.

Solve for x and then divide by 2 for the current...I'm not sure if that would be correct so the safest way is probably a Norton equivalent whereby you convert the voltage sources to current sources and place the corresponding resistances in parallel...this should let you add the three resistors in parallel and you should be able to deduce the current from that.

Tokyo

Presume an arbitrary current in the LHS and RHS loops (I1 and I2 respectively)

Use Kirchoff's Voltage Law to solve for I1 and I2


Current through R2 is the sum of I1 and I2 (assuming you set up I1 and I2 to pass through R2 in the same direction)

Assuming my maths is correct, the solution is here, if you want to take a look.

brightspark

Some of you are missing the point, I have already looked up how to do it.

I wanted to know if anyone else had had to relearn how to do something that they once knew well.

Cerco

Did you also forget the Norton equivalent circuit? I like this thread and enjoy working through these problems, it keeps the old mind active. I am sure there are loads of things I've forgotten but I just can't remember them now

brightspark

Cerco wrote: »

Did you also forget the Norton equivalent circuit? I like this thread and enjoy working through these problems, it keeps the old mind active. I am sure there are loads of things I've forgotten but I just can't remember them now

I don't think I ever really learnt the Norton version

Bad enough to have forgotten how to use one theorem, imagine having wasted time learning both, never to use either again after the Senior Trades!

2011

brightspark wrote: »

I wanted to know if anyone else had had to relearn how to do something that they once knew well.

Affirmative

It is always easier to relearn that to learn for the first time.

dingding

I had forgotten all this but now that I see it and the discussion I remember some of it.

.G.

I pretty much forget everything on the electrical science side of things bar the stuff I would use sometimes.Electronic stuff and the vast majority of 3 phase electrical science stuff have long since left my head through lack if use for them in my daily work.Might need a 3 phase power calc from time to time but little else.I still have all my notes+books from college phase's though so I could refresh if the need arose.

On the practical side of things,having never spent time in a big company like Mercury and the like I have forgotten how to do bends/jumps etc in conduit because the only time I ever did it was a week in phase 2 in 2008!

Iderown

Plenty that's a bit rusty from not getting used very often. (Insert smiley face here.)
Shout at me if you need:
Solving that type of circuit by using loops and Ohm's stuff or by using superposition stuff. I hope you get the same answer.
Other items easily left behind are phasor diagrams and Laplace transforms.