Need homework help...(electrical)

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01-26-2005, 12:37 PM

Thumper89

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Right now we are taking electrical in school...YEA!!

Well...Sort of...

I still don't get how to total resistance in a parallel and a series-parallel circuit with the resistance factors knows...

I've tried calling a couple people,and one was able to semi-explain in terms I understand, but if someone could show me in writing,I think I could understand a little better...

I'll leave 2 examples here..one of each...and yes,this right from my homework...

Parallel:
9:What is the total resistance in a parallel circuit that has the following resistors-R1=4 ohm and R2=2 ohm?

15:What is the total resistance in a series-parallel circuit that has the following reistors:R1 is 1/2 ohm and R2 is 3/4ohm(in a series circuit)with the parallel resistors R3 is 1/3ohm and R4 is 1/4 ohm?

I'm going to continue to fight with this and see what I ca find on the net, and I will check back here every so often....

THANKS SOOOO MUCH TO WHOEVER MAYBE ABLE TO HELP ME OUT WITH THIS!! [img]graemlins/beer.gif[/img]

01-26-2005, 01:26 PM

Haunz

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Quote:

What is the total resistance in a parallel circuit that has the following resistors-R1=4 ohm and R2=2 ohm?

What is the total resistance in a series-parallel circuit that has the following reistors:R1 is 1/2 ohm and R2 is 3/4ohm(in a series circuit)with the parallel resistors R3 is 1/3ohm and R4 is 1/4 ohm?

For # 1 add the reciprials and take the reciprical of what you get.... 1/4 + 1/2 = 3/4... the reciprical of 3/4 is 4/3 which is equal to 1.33

For # 2 R1 and R2 add up to 1.25ohms if R3 and R4 are in parallel, along with R1 and R2 (in series) you get:

1/[1/1.25 + 1/.333 + 1/.25] = 1.28 ohms

01-26-2005, 01:44 PM

Thumper89

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Yeah..I found a site that helped me figure the parallel circuit out no problem...

http://www.rsc-northwest.ac.uk/Curri...20circuits.doc

I still don't get the S/P circuit...

Sorry...I'm one of those people that needs things explained in math one single step at a time...Never been any good with numbers for the most part...

Sorry,Haunz...What you have written still just goes over my head...But I'm not giving up!!

Thanks for the try though...it truly is appreciated..

01-26-2005, 01:46 PM

Livin - Loud

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^^ that looks correct!

BTW i got your msg aaron. bu ti was at schooL! LOL.. at least u found out what u needed to know

Livin Loud

01-26-2005, 02:00 PM

Thumper89

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Ok...I think I have a good idea on the S/P circuit now...

Heres the question I just did...let me know if I'm doing it right....

Seried resistors=R1=1.5ohms and R2=3.5ohms
Parallel resis.=R3=4ohm and R4=5ohm

Here's my solution:
Rts=Resistance total series
Rtp=Resistance total parallel

Rts=1.5ohm + 3.5ohm = 5ohm

Rtp=1/4ohm + 1/5ohm= 5/20 + 4/20= 9/20= 20/9= 20 divided by 9= 2.22ohms

Rt=Rts + Rtp= 5ohm + 2.22= 7.22ohms

Is this right??

01-26-2005, 02:07 PM

Paul Niwranski

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Quote:

What is the total resistance in a series-parallel circuit that has the following reistors:R1 is 1/2 ohm and R2 is 3/4ohm(in a series circuit)with the parallel resistors R3 is 1/3ohm and R4 is 1/4 ohm?

The wording of that problem is ambiguous. My best guess is that it is as Haunz stated - except Haunz made a mathmatical error [img]tongue.gif[/img]

R1 and R2 are in series:
Rx = R1 + R2
Rx = 1/2 + 3/4
Rx = 2/4 + 3/4
Rx = 5/4

Rt is in parallel with R3 and also in parallel with R4

1/Rt = 1/Rx + 1/R3 + 1/R4
1/Rt = 4/5 + 3/1 + 4/1
1/Rt = 4/5 + 15/5 + 20/5
1/Rt = 39/5
Rt = 5/39
Rt = 0.128

Or if you prefer a calculator:
Rx = 5/4 = 1.25
R3 = 1/3 = 0.333
R4 = 1/4 = 0.25

1/Rt = (1/1.25) + (1/0.333) + (1/0.25)
1/Rt = 0.8 + 3 + 4
1/Rt = 7.8
1 = Rt * 7.8
1/7.8 = Rt
0.128 = Rt

01-26-2005, 02:58 PM

Thumper89

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Sorry Dukk...But....

HUH???

[img]graemlins/dunno.gif[/img] [img]graemlins/banghead.gif[/img]

01-26-2005, 05:24 PM

Gmac

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if the parallel resistors are in series with the series resistors then yes it is correct.

Any time you have resisters in series solve only that portion of the circuit and redraw the circuit with the parallel resistors replaced with one resistor and give it the value you solved the parallel circuit for

01-26-2005, 05:26 PM

Gmac

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it looks like duke put the series resistors in parallel with the parallel resistors

01-26-2005, 05:47 PM

#10

Thumper89

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Quote:

Originally posted by Aaronski Birdmanovich:
Ok...I think I have a good idea on the S/P circuit now...

Heres the question I just did...let me know if I'm doing it right....

Seried resistors=R1=1.5ohms and R2=3.5ohms
Parallel resis.=R3=4ohm and R4=5ohm

Here's my solution:
Rts=Resistance total series
Rtp=Resistance total parallel

Rts=1.5ohm + 3.5ohm = 5ohm

Rtp=1/4ohm + 1/5ohm= 5/20 + 4/20= 9/20= 20/9= 20 divided by 9= 2.22ohms

Rt=Rts + Rtp= 5ohm + 2.22= 7.22ohms

Is this right??

Isnt it easier to try and solve it like this....

and still noone has told me if I have it right....hehehe.....

BTW...WTF is RX mean?

RT=Resistance total
Rtp=" "parallel
Rts=" "series
Rn= [img]graemlins/dunno.gif[/img]
Rx= [img]graemlins/dunno.gif[/img]

Either way...There has to be an easier way...this just stupid!!

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