OCR AS Physics B electricity help please Watch

londoncricket
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Hi all,

Please look at the attached screenshot. I do not understand how I would arrive at these values for V1 and V2 (quoting from "Answers" section of the book):

I1 = 0.3
V1 = 3.4
V2 = 2.6

Thank you!
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The-Spartan
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So you understand that \sideset{}{_1} I = 0.3 from basic principles.
Now you have 0.3A going through \sideset{}{_1} V and 0.4A going through \sideset{}{_2} V

Conservation proof:
As the loop that contains \sideset{}{_1} V has to equal \sideset{}{in} V = 3.4,
\sideset{}{_1} V = 3.4
and so \sideset{}{_2} V = 2.6 from the conservation of the entire loops EMF.

\sideset{}{_1} I = 0.3
\sideset{}{_1} V = 3.4
\sideset{}{_2} V = 2.6
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derpz
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(Original post by londoncricket)
Hi all,

Please look at the attached screenshot. I do not understand how I would arrive at these values for V1 and V2 (quoting from "Answers" section of the book):

I1 = 0.3
V1 = 3.4
V2 = 2.6

Thank you!
Voltage across parallel sections is the same so the V1 = 3.4 too, then work out the overall resistance and the resistance of the parallel bit.

Find the difference between them and that is the resistance of V2, then simply use V=IR to get the pd.
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londoncricket
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(Original post by The-Spartan)
So you understand that \sideset{}{_1} I = 0.3 from basic principles.
Now you have 0.3A going through \sideset{}{_1} V and 0.4A going through \sideset{}{_2} V

Conservation proof:
As the loop that contains \sideset{}{_1} V has to equal \sideset{}{in} V = 3.4,
\sideset{}{_1} V = 3.4
and so \sideset{}{_2} V = 2.6 from the conservation of the entire loops EMF.

\sideset{}{_1} I = 0.3
\sideset{}{_1} V = 3.4
\sideset{}{_2} V = 2.6
(Original post by derpz)
Voltage across parallel sections is the same so the V1 = 3.4 too, then work out the overall resistance and the resistance of the parallel bit.

Find the difference between them and that is the resistance of V2, then simply use V=IR to get the pd.
Thank you both very much for your explanations!

I still do not understand why V1 = 3.4V, though. Could you please explain this a bit further?

Thank you!
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bookworm21
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Because we are looking at the 'potential difference' between two points when we look at 'voltages' across components.

As the ends of both resistors are connected directly they must be at the same 'potential' and so the potential difference across both resistors must be the same.

I hope that has cleared this up for you, if not I can try to explain further
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