A level Physics Electricity Question Watch

kinghulio
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Question 16, Multiple choice question which I don't really understand. I have the answer already but don't understand how to get there. I tried subbing the given variables into V=IR etc, which didn't really help.

https://drive.google.com/file/d/1hlN...ew?usp=sharing

The Choices are
A - I/3
B - 4I/9
C- I/2
D - 2I/3

(Incase it's not clear in the picture)
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Idg a damn
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I think it might be A
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Idg a damn
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what's the answer ?
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kinghulio
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(Original post by Idg a damn)
what's the answer ?
You're right, the answer is A. How'd do you do it?
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Callicious
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Consider the first circuit
Draw it
Find that 4 IR = 3 V
Second circuit drawn
Now in reverse, the cell PD opposes the other two cells
2V - 1 = 4 iR (new I = i)
Ratio of 1V / 3V = i/I = 1/3 = ratio of currents
Hence 1/3
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Idg a damn
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Let the e.m.f. of one battery be V

As such total e.m.f of circuit is 3V

Total resistance for circuit is 4R

As such 3V/4R = I

Now one battery is inverted , as such current by two batteries will flow in one direction, the current by the other battery will flow in the opposite direction .

Current by 2 batteries is 2V/4R =2I/3

Current by 1 battery is V/4R =I/3

Since current is a vector quantity , effective current is (2I/3) -( I/3) = I/3
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kinghulio
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(Original post by Callicious)
Name:  Capture.PNG
Views: 27
Size:  69.4 KB

Consider the first circuit
Draw it
Find that 4 IR = 3 V
Second circuit drawn
Now in reverse, the cell PD opposes the other two cells
2V - 1 = 4 iR (new I = i)
Ratio of 1V / 3V = i/I = 1/3 = ratio of currents
Hence 1/3
https://drive.google.com/file/d/1iUA...ew?usp=sharing
Got it. Thank you again appreciate it
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kinghulio
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(Original post by Idg a damn)
Let the e.m.f. of one battery be V

As such total e.m.f of circuit is 3V

Total resistance for circuit is 4R

As such 3V/4R = I

Now one battery is inverted , as such current by two batteries will flow in one direction, the current by the other battery will flow in the opposite direction .

Current by 2 batteries is 2V/4R =2I/3

Current by 1 battery is V/4R =I/3

Since current is a vector quantity , effective current is (2I/3) -( I/3) = I/3
Thank you for your help, it makes sense now.
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