Any tips ?? Remembering formula

Paddy4444 · Dec 12, 2018

Hey I’m studying 2365 at college and I’m at the science part now .. any tips on remembering formula or is it just a case of going over and over it till it’s in your head .. any help much appreciated

MFS Electrical · Dec 12, 2018

Jay 1987 said:
Hey paddy I believe we are in the same position !

I started my level 2 in September and have been going over and over the theory as telectrix stated and believe it or not it does start to sink in

Maybe we could have some theory questions based on formula suitable for “level 2 students”
From some of the more experienced guys!

Just a thought.....

So far we have covered powers, ohms law triangle, power triangle, working out energy, work done, but the hardest for me is deffo transposition!

I have looked at some of the electrical design questions on the trainee section! But they are a little advanced for me at the moment!

But I still read it to get a flavour for real life scenarios

Even though you may think they are a bit advanced just have a bash. a wise man once told me you learn best by making an a**e of it. get it wrong and we can show you where you went off the tracks get it right and that’s all good. How will you know if you never even try!

Jay 1987 · Dec 12, 2018

Very true can’t argue with that !

Silly Sausage · Dec 12, 2018

MFS Electrical said:
Even though you may think they are a bit advanced just have a bash. a wise man once told me you learn best by making an a**e of it. get it wrong and we can show you where you went off the tracks get it right and that’s all good. How will you know if you never even try!

Confucius say, "If it too easy now, it bite you on arse later"

MFS Electrical · Dec 12, 2018

Archy Styrigg said:
Confucius say, "If it too easy now, it bite you on arse later"

Is it bad that I read that with the accent

That’s what this part of the forum is for no matter how daft your reply is we won’t bite we are only looking to help but we can’t do that if no one is gonna try

Jay 1987 · Dec 12, 2018

Lucien Nunes said:
You need to take more care over details in engineering. 5kW what? Input? Output? a '5kW' motor, that would usually mean the mechanical output rating. A 5kW heater, that would be input power. Presumably 230 means 230V single-phase AC but you don't say that. 24A with what power factor or is this DC?

If I rephrase the question as:
A device uses 24A at unity power factor from a 230V single-phase AC supply and outputs 5kW useful power. What it its efficiency?

Now it can be calculated because I've filled in the missing info.

Input power = V.I.cos(phi)
Efficiency = useful output power / input power
=5000 / (230 x 24 x 1)
=91%

Thanks it was a question I remembered from my exam, as everybody got it wrong! Hence the reason I relayed it incorrectly.

The formula we learnt to work out efficiency
Was

Output power
————————. X 100
Input power

But we never knew how to work out input power from volts and amps

Using power triangle I understand

P
I V

But I don’t understand the p = v2 part

And where did you get 1 from

5000/ (230 x 24 x 1?)

Silly Sausage · Dec 12, 2018

V=IR
I=V/R
P=VI
substitute I with V/R gives you ...
P=V * V/R = (V^2)/R

^2 is to the power of 2, ie V squared.

Edtwozeronine · Dec 13, 2018

Dropbox - Electrical Science.pdf - https://www.dropbox.com/s/69sr9tof37moj6p/Electrical%20Science.pdf?dl=0 Use this for walk throughs on all things electrical science.

Deleted member 72666 · Dec 13, 2018

Some of you may find this useful when typing mathematical symbols.
Type mathematical symbols - online keyboard - http://math.typeit.org/

Jay 1987 · Dec 13, 2018

Archy Styrigg said:
V=IR
I=V/R
P=VI
substitute I with V/R gives you ...
P=V * V/R = (V^2)/R

^2 is to the power of 2, ie V squared.

I see what you’ve done, but I don’t understand what you’ve done!

What’s the need to substitute I for V

In what situation would you use V2?

Richard Burns · Dec 13, 2018

Jay 1987 said:
I see what you’ve done, but I don’t understand what you’ve done!

What’s the need to substitute I for V

In what situation would you use V2?

The variations in formulae are to account for the known variables.
On a piece of equipment designed for 230V ac if you use an ohmmeter to measure the resistance of the load then you now know two variables, R and V, if you want to know the power then you can use P=V²/R.
It would also be possible to get I from I = V/R and then use this calculated value for I in the P = VI equation but then you have to do two calculations.
Effectively you do the first calculation, I=V/R, in advance by substituting V/R for I in the P=VI equation.
Other versions of the equations can be used where you know different values.

telectrix · Dec 13, 2018

as richard burns said. if you know R but don't know I, then as above.

Silly Sausage · Dec 13, 2018

@stantheman

Cheers Stan

Spunkywads26 · Dec 13, 2018

I am teaching electrical science at the minute with my students and have just covered ohms law, series, parallel, series+parallel and power.

I have found that it is easy for them to remember ohms law (V = I x R) and power formula (P = V x I). I then say that they can either remember the other 2 power formulas (P = I^2 x R & P = V^2/R) or if they can transpose and substitute formula then they only need the 1st two formula to work out the rest.

telectrix · Dec 14, 2018

this might be useful.:

[ElectriciansForums.net] Any tips ?? Remembering formula

satori · Dec 16, 2018

Paddy4444 said:
Hey I’m studying 2365 at college and I’m at the science part now .. any tips on remembering formula or is it just a case of going over and over it till it’s in your head .. any help much appreciated

Flash cards. That's what I used. Have a Google, there's software that lets you make your own. It helps having a buddy so you can each test each other. I found it worked very quickly. I can't remember any of them now - well, apart from Ohms Law, and power.

delano · Dec 22, 2018

Paddy4444 said:
Hey I’m studying 2365 at college and I’m at the science part now .. any tips on remembering formula or is it just a case of going over and over it till it’s in your head .. any help much appreciated

Learn transposition.

telectrix · Dec 22, 2018

delano said:
Learn transposition.

the gender bender website will have all the info.

.

Any tips ?? Remembering formula

Paddy4444

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MFS Electrical

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Jay 1987

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Silly Sausage

MFS Electrical

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Jay 1987

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Silly Sausage

Edtwozeronine

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Deleted member 72666

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Jay 1987

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Richard Burns

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telectrix

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Silly Sausage

Spunkywads26

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telectrix

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satori

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delano

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telectrix

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