Go Back   Physics Help Forum > College/University Physics Help > General Physics

General Physics General Physics Help Forum

Like Tree8Likes
Reply
 
LinkBack Thread Tools Display Modes
Old Apr 29th 2018, 04:44 AM   #1
Junior Member
 
Join Date: Apr 2018
Posts: 13
Resistance combinations help

Resistance combinations help-asd.png
A little bit confusing the way this circuit was set up
if you can help it would be great
questions are
equivalent resistance
current through 18 and 12 ohms resistor
power dissipation in 4.5 ohm
Musawwir is offline   Reply With Quote
Old Apr 29th 2018, 05:06 AM   #2
Senior Member
 
Join Date: Apr 2015
Location: Somerset, England
Posts: 995
A little bit confusing the way this circuit was set up
Never be afraid to redraw the circuit, perhaps more than once.

This would be a good start.

Can you see a series or parallel combination that would simplify it?

Also label your components. It is easier to refer to R2 than "the 25ohm resistor"

and R5 is easier than "the parallel combination of ...."

Ask again if you need more help
Attached Thumbnails
Resistance combinations help-q3.jpg  
topsquark and Musawwir like this.
studiot is offline   Reply With Quote
Old Apr 29th 2018, 05:28 AM   #3
Junior Member
 
Join Date: Apr 2018
Posts: 13
thank you now it looks so much easier
so could you pls check if these are right
current through 18 ohms is just 6/18 A
and 12 ohms is just 6/12 A
and power dissipation is (R3)^3(36)/R1+R3
and equivalent resistance is 7.41 ohm?

Last edited by Musawwir; Apr 29th 2018 at 01:24 PM.
Musawwir is offline   Reply With Quote
Old Apr 29th 2018, 05:35 AM   #4
Senior Member
 
Join Date: Apr 2015
Location: Somerset, England
Posts: 995
Originally Posted by Musawwir View Post
thank you now it looks so much easier
so could you pls check if these are right
current through 18 ohms is just 6/18 A
and 12 ohms is just 6/12 A
and power dissipation is (R3)^3(36)/R1+R1
and equivalent resistance is 7.41 ohm?
I don't think you have got it yet.

Yes the current through R4 is 6/18 amps.

But the current through R1 is not 6/12 amps.

Since there are several methods to solve this please indicate how you are approaching this so we can make your method work.
Musawwir likes this.
studiot is offline   Reply With Quote
Old Apr 29th 2018, 05:56 AM   #5
Senior Member
 
Join Date: Apr 2015
Location: Somerset, England
Posts: 995
What's the problem?
studiot is offline   Reply With Quote
Old Apr 29th 2018, 01:20 PM   #6
Junior Member
 
Join Date: Apr 2018
Posts: 13
Originally Posted by studiot View Post
I don't think you have got it yet.

Yes the current through R4 is 6/18 amps.

But the current through R1 is not 6/12 amps.

Since there are several methods to solve this please indicate how you are approaching this so we can make your method work.
here is my re worked solution
Resistance combinations help-solution.jpg
Musawwir is offline   Reply With Quote
Old Apr 29th 2018, 01:53 PM   #7
Senior Member
 
Join Date: Apr 2015
Location: Somerset, England
Posts: 995
here is my re worked solution
Well sort of.

Here are the stages I worked through to get R7, the equivalent resistance.

Can you see how I have built it up in stages, one step at a time?

You need this for the later parts of the question.

Do you understand that each of the redrawn circuits are equivalent to the first one?
Attached Thumbnails
Resistance combinations help-q3_2.jpg  
Musawwir likes this.
studiot is offline   Reply With Quote
Old Apr 30th 2018, 03:43 AM   #8
Junior Member
 
Join Date: Apr 2018
Posts: 13
yes i got it thank you
Musawwir is offline   Reply With Quote
Old Apr 30th 2018, 04:00 AM   #9
Senior Member
 
Join Date: Apr 2015
Location: Somerset, England
Posts: 995
Originally Posted by Musawwir View Post
yes i got it thank you
OK so the next thing to do is to calculate the total current.

Do you know how to do this?
studiot is offline   Reply With Quote
Old Apr 30th 2018, 07:30 AM   #10
Junior Member
 
Join Date: Apr 2018
Posts: 13
yes you just take the equivalent resistance divide by the voltage
Musawwir is offline   Reply With Quote
Reply

  Physics Help Forum > College/University Physics Help > General Physics

Tags
combinations, ohms law, resistance



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
resistance gordonmckee Electricity and Magnetism 2 Oct 13th 2014 09:44 AM
need some help with this one on resistance gordonmckee Electricity and Magnetism 1 Aug 14th 2014 08:27 AM
Resistance... ppsolanke Electricity and Magnetism 0 Aug 23rd 2012 03:03 AM
Zero Resistance anwaar Electricity and Magnetism 5 Feb 9th 2011 02:34 PM
Different Combinations of resistances Xenophilius Electricity and Magnetism 1 Oct 22nd 2009 11:12 PM


Facebook Twitter Google+ RSS Feed