# A level Physics Electricity Question

Watch
#1
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.

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

(Incase it's not clear in the picture)
0
1 year ago
#2
I think it might be A
0
1 year ago
#3
0
#4
(Original post by Idg a damn)
You're right, the answer is A. How'd do you do it?
0
1 year ago
#5

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
0
1 year ago
#6
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
0
#7
(Original post by Callicious)

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
Got it. Thank you again appreciate it
0
#8
(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.
0
X

new posts Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### How are you feeling ahead of results day?

Very Confident (28)
8.31%
Confident (44)
13.06%
Indifferent (51)
15.13%
Unsure (82)
24.33%
Worried (132)
39.17%