DanielDaniels
Badges: 14
Rep:
?
#1
Report Thread starter 6 years ago
#1
I found this question posted by StoneBridge some where. Anyway, I didn't really quite get it because I just confused things up and that's due to my lack of understanding to certain topics.

How i thought about it is using the idea of short circuit which is totally wrong, but i want to know why it won't work here? and if can be explained by it, how?
Image
Attached files
0
reply
RoyalBlue7
Badges: 19
Rep:
?
#2
Report 6 years ago
#2
It looks like only the middle resistor wouldn't work while the other two are in fact parallel with each other?
0
reply
uberteknik
  • Study Helper
Badges: 21
Rep:
?
#3
Report 6 years ago
#3
(Original post by Daniel Atieh)
I found this question posted by StoneBridge some where. Anyway, I didn't really quite get it because I just confused things up and that's due to my lack of understanding to certain topics.

How i thought about it is using the idea of short circuit which is totally wrong, but i want to know why it won't work here? and if can be explained by it, how?
Image
Think of the problem as one of voltages and currents. Using one terminal as a reference, what would the potential differences (voltage drops) around the circuit look like? Where would the current flow in a dc circuit first and then consider the same question for an ac circuit.

HINT:

Spoiler:
Show

Try redrawing the circuit with a dc power source on the lhs between A and B and the three resistors arranged on the other three sides of a square. Finally draw in the conductors and follow the current paths around the formed loops according to Kirchoff's rules.

The s/c's definitely need to be taken into account and you can work out the resistance by inspection alone for both ac and dc.
0
reply
DanielDaniels
Badges: 14
Rep:
?
#4
Report Thread starter 6 years ago
#4
(Original post by uberteknik)
Think of the problem as one of voltages and currents. Using one terminal as a reference, what would the potential differences (voltage drops) around the circuit look like? Where would the current flow in a dc circuit first and then consider the same question for an ac circuit.

HINT:

Spoiler:
Show

Try redrawing the circuit with a dc power source on the lhs between A and B and the three resistors arranged on the other three sides of a square. Finally draw in the conductors and follow the current paths around the formed loops according to Kirchoff's rules.

The s/c's definitely need to be taken into account and you can work out the resistance by inspection alone for both ac and dc.
First of all, many thanks for your help, man!

I'm pretty weak in this topic and I didn't quite follow all your points :/

When i first saw this question, i just followed the path of the current and imagined it in this way (which looks silly and incorrect):
Image
So according to this diagram i drew, each resistor will receive a different current and therefore they re in parallel (i.e total R is R/3). I indicated each current by a different colour. So is my approach at least close to the correct way?

I m sorry, but as i said, am weak in this topic and your help here might contribute to a massive improvement in my understanding in such problems.

Thanks a ton once again!
Attached files
0
reply
DanielDaniels
Badges: 14
Rep:
?
#5
Report Thread starter 6 years ago
#5
(Original post by RoyalBlue7)
It looks like only the middle resistor wouldn't work while the other two are in fact parallel with each other?
I also thought like that in the first place, but the answer is R/3. I still didn't quite get how to approach to this answer exactly :/
0
reply
natninja
Badges: 21
Rep:
?
#6
Report 6 years ago
#6
(Original post by Daniel Atieh)
First of all, many thanks for your help, man!

I'm pretty weak in this topic and I didn't quite follow all your points :/

When i first saw this question, i just followed the path of the current and imagined it in this way (which looks silly and incorrect):
Image
So according to this diagram i drew, each resistor will receive a different current and therefore they re in parallel (i.e total R is R/3). I indicated each current by a different colour. So is my approach at least close to the correct way?

I m sorry, but as i said, am weak in this topic and your help here might contribute to a massive improvement in my understanding in such problems.

Thanks a ton once again!
It's sort of nearly there and gets the correct answer, you got the current loops going in the correct directions at least (though it actually doesn't usually matter).

Essentially all linear circuit problems come down to kirchoff's laws and the laws governing the components:

1. The sum of currents flowing into a node is zero. (Alternatively current into any point in a circuit is equal to the total current going out of it)
2. The voltage drop around ANY CLOSED loop is zero.
1
reply
atsruser
Badges: 11
Rep:
?
#7
Report 6 years ago
#7
(Original post by Daniel Atieh)
I also thought like that in the first place, but the answer is R/3. I still didn't quite get how to approach to this answer exactly :/
Let the voltage at A be V volts and that at B be 0 volts. The note that:

a) the 2nd node from the left is connected to B by a path of no resistance, so what is its potential?

b) the same question for the 3rd node from the left.

So

1. in which direction does the current flow through the central resistor and what is its magnitude?

2. the same question for the left and right hand resistors

That should give you enough info.
1
reply
DanielDaniels
Badges: 14
Rep:
?
#8
Report Thread starter 6 years ago
#8
(Original post by natninja)
It's sort of nearly there and gets the correct answer, you got the current loops going in the correct directions at least (though it actually doesn't usually matter).

Essentially all linear circuit problems come down to kirchoff's laws and the laws governing the components:

1. The sum of currents flowing into a node is zero. (Alternatively current into any point in a circuit is equal to the total current going out of it)
2. The voltage drop around ANY CLOSED loop is zero.
(Original post by atsruser)
Let the voltage at A be V volts and that at B be 0 volts. The note that:

a) the 2nd node from the left is connected to B by a path of no resistance, so what is its potential?

b) the same question for the 3rd node from the left.

So

1. in which direction does the current flow through the central resistor and what is its magnitude?

2. the same question for the left and right hand resistors

That should give you enough info.
Thanks a lot guys for your help

So...

As the voltage drop in each loop is zero, so each of the resistors receives full voltage say V and therefore they re therefore in a parallel connection right?
0
reply
natninja
Badges: 21
Rep:
?
#9
Report 6 years ago
#9
(Original post by Daniel Atieh)
Thanks a lot guys for your help

So...

As the voltage drop in each loop is zero, so each of the resistors receives full voltage say V and therefore they re therefore in a parallel connection right?
Essentially you can write an equation for every closed loop in the circuit and then when you have enough you can solve them simultaneously.
0
reply
RoyalBlue7
Badges: 19
Rep:
?
#10
Report 6 years ago
#10
(Original post by Daniel Atieh)
I also thought like that in the first place, but the answer is R/3. I still didn't quite get how to approach to this answer exactly :/
Lol I forgot about Kirchhoof's (?) laws. Didn't realize that the current could flow the other way through the middle resistor.
0
reply
atsruser
Badges: 11
Rep:
?
#11
Report 6 years ago
#11
(Original post by Daniel Atieh)
Thanks a lot guys for your help

So...

As the voltage drop in each loop is zero, so each of the resistors receives full voltage say V and therefore they re therefore in a parallel connection right?
Yes, this is simply a parallel arrangement of 3 resistors redrawn to disguise that fact.
0
reply
Stonebridge
Badges: 13
Rep:
?
#12
Report 6 years ago
#12
Yes, I did post this question some years ago.
Here's the original post and the replies.
http://www.thestudentroom.co.uk/show...php?p=31142023
Yes, they are just 3 resistors in parallel.
Image
0
reply
DanielDaniels
Badges: 14
Rep:
?
#13
Report Thread starter 6 years ago
#13
(Original post by atsruser)
Yes, this is simply a parallel arrangement of 3 resistors redrawn to disguise that fact.
Yes, man. Can you show me how to write the equations and then solve them simultaneously using the example i posted above?


Posted from TSR Mobile
0
reply
DanielDaniels
Badges: 14
Rep:
?
#14
Report Thread starter 6 years ago
#14
(Original post by Stonebridge)
Yes, I did post this question some years ago.
Here's the original post and the replies.
http://www.thestudentroom.co.uk/show...php?p=31142023
Yes, they are just 3 resistors in parallel.
Image
Thank you!
Can you show me how i can develop two equations and then solve them simultaneously pls.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

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

Personalise

Today on TSR

Have you experienced financial difficulties as a student due to Covid-19?

Yes, I have really struggled financially (61)
17.23%
I have experienced some financial difficulties (98)
27.68%
I haven't experienced any financial difficulties and things have stayed the same (136)
38.42%
I have had better financial opportunities as a result of the pandemic (48)
13.56%
I've had another experience (let us know in the thread!) (11)
3.11%

Watched Threads

View All