Ava_Watson
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Can someone explain how to do 4cName:  1632057016990.jpg
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mqb2766
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You have two equations for R1 and R2, so write them down and solve them simultaneously.
Post your progress if you get stuck.
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chinjyanson
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They gave us that these resistors are in parallel, and hence the Total resistance, T, will have the formula of 1/T = 1/R1 + 1/R2. We know that R1=R1 and we know that R2 = R1 + 3. So subbing this in to the formula that they gave us:
1/T = 1/R1 + 1/(R1+3)
Through simplification we can rearrange to get T= (R1^2 + 3R1)/2R1+3. Now sub in R1 = 1 + 1/8 in the equation to find T
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mqb2766
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(Original post by chinjyanson)
They gave us that these resistors are in parallel, and hence the ...
A bit like your other post, can you edit/delete and just provide hints and let the OP do as much of the work as possible?
The guidelines are described in the sticky at the top of the forum.
https://www.thestudentroom.co.uk/sho....php?t=4919248
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Ava_Watson
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(Original post by mqb2766)
You have two equations for R1 and R2, so write them down and solve them simultaneously.
Post your progress if you get stuck.
Name:  1632210755990.jpg
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Size:  160.1 KBthis is what I got so far
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Ava_Watson
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(Original post by chinjyanson)
They gave us that these resistors are in parallel, and hence the Total resistance, T, will have the formula of 1/T = 1/R1 + 1/R2. We know that R1=R1 and we know that R2 = R1 + 3. So subbing this in to the formula that they gave us:
1/T = 1/R1 + 1/(R1+3)
Through simplification we can rearrange to get T= (R1^2 + 3R1)/2R1+3. Now sub in R1 = 1 + 1/8 in the equation to find T
Shouldn't it be x3 not +3?
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mqb2766
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Main mistake is when you add (combine) two fractions. If the two resistors are A and B
1/A + 1/B = ...
Simply add the fractions as normal. I'd do the substition about one resistor being 3 greater (+3), when you've got the basic algebra done.

Its also easier to write 1 1/8 in improper form.
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Ava_Watson
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(Original post by chinjyanson)
They gave us that these resistors are in parallel, and hence the Total resistance, T, will have the formula of 1/T = 1/R1 + 1/R2. We know that R1=R1 and we know that R2 = R1 + 3. So subbing this in to the formula that they gave us:
1/T = 1/R1 + 1/(R1+3)
Through simplification we can rearrange to get T= (R1^2 + 3R1)/2R1+3. Now sub in R1 = 1 + 1/8 in the equation to find T
Name:  1632211096313.jpg
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Size:  102.7 KB so according to u I should do what's on the right side
But I don't get how u got last equation
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mqb2766
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One resisitor is +3 Ohms larger than the other one, not 3 times larger. Also it does not look like you're adding fractions correctly.

You seem to have copied the last expression on the page from the earllier post, but your working is incorrect to get there.


R_2 = R_1 + 3
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Ava_Watson
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(Original post by mqb2766)
One resisitor is +3 Ohms larger than the other one, not 3 times larger. Also it does not look like you're adding fractions correctly.

You seem to have copied the last expression on the page from the earllier post, but your working is incorrect to get there.


R_2 = R_1 + 3
I see
Appreciate the help
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Ava_Watson
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#11
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(Original post by mqb2766)
Not a good idea give your details on line.
Its just an email address
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mqb2766
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(Original post by Ava_Watson)
Its just an email address
Sure, its a new user whos spamming several forums and is likely to be banned shortly.
Your shout though.
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