The Sum of Capacitance Question Help Pls

Announcements
Thread starter 5 months ago
#1
I have to sum the capacitance (The answer is 400 and I keep getting 300). no idea how else to approach lol

sorry! no idea y it's upside down...
Last edited by Obolinda; 5 months ago
0
5 months ago
#2
Do you not have 3 in series which are in parallel with the other one? Second picture.
0
Thread starter 5 months ago
#3
(Original post by BlueChicken)
Do you not have 3 in series which are in parallel with the other one? Second picture.
the second picture was me trying to draw what I thought was an equivalent circuit to make the question easier to do. this is the original q:
0
5 months ago
#4
(Original post by Obolinda)
the second picture was me trying to draw what I thought was an equivalent circuit to make the question easier to do. this is the original q:
oh, I meant second, if we turn both pictures as are the correct way up! That's the picture I was referring to.

So, imagine 2 capacitors top and bottom of the picture are drawn next to the one on the left - there are 3 capacitors in series, which are in parallel with the one on the right. Just looking at the answer, the maths appears to be [1/(3/300)] + 300, which would tie with the above. Does that make sense?
1
Thread starter 5 months ago
#5
(Original post by BlueChicken)
oh, I meant second, if we turn both pictures as are the correct way up! That's the picture I was referring to.

So, imagine 2 capacitors top and bottom of the picture are drawn next to the one on the left - there are 3 capacitors in series, which are in parallel with the one on the right. Just looking at the answer, the maths appears to be [1/(3/300)] + 300, which would tie with the above. Does that make sense?
that makes sense thank you! i just don't know how id answer a question like this in the future, how did you know to think of the circuit as 3 capacitors in series parallel to 1 capacitor ?
0
5 months ago
#6
I think you've probably not paid enough attention to where the test points are in relation to the components...

0
5 months ago
#7
... so you need to combine the caps in series that I've called B,C &D

and then combine that equivalent value with the capacitor A that it's in parallel with.
1
5 months ago
#8
(Original post by Obolinda)
that makes sense thank you! i just don't know how id answer a question like this in the future, how did you know to think of the circuit as 3 capacitors in series parallel to 1 capacitor ?
So, first way, practice! The logical way, is to consider the current/charge going through them (these are how the laws are derived). In the diagram, assume current is flowing from R to S (assume they are just points and R and S don't refer to anything - I feel like they threw those in as a trick). The top junction, i.e. the black dot at top, the current will split, i.e. some current will go through 3 of the resistors in a line and the rest will go through the resistor on the right (here, we don't care about sizes of current/charge, just where it is going). Therefore, 3 are in series and are in parallel with the other one.

This link has pictures for what I mean about the charge (therefore, current) splitting: https://courses.lumenlearning.com/ph...-and-parallel/
Last edited by BlueChicken; 5 months ago
0
Thread starter 5 months ago
#9
(Original post by Joinedup)
I think you've probably not paid enough attention to where the test points are in relation to the components...

(Original post by BlueChicken)
So, first way, practice! The logical way, is to consider the current/charge going through them (these are how the laws are derived). In the diagram, assume current is flowing from R to S (assume they are just points and R and S don't refer to anything - I feel like they threw those in as a trick). The top junction, i.e. the black dot at top, the current will split, i.e. some current will go through 3 of the resistors in a line and the rest will go through the resistor on the right (here, we don't care about sizes of current/charge, just where it is going). Therefore, 3 are in series and are in parallel with the other one.
ahh... i see. i think i get this now. thank you very much guys, you are life savers !!!
0
5 months ago
#10
Maybe think of circuit diagrams as being like tube maps with the components for the stations *

if the train comes in from the left and goes right at the first junction it has to go through B and then C and then D... cos those 3 are in series.

* The guy who designed the 'iconic' modern london tube map was IIRC an electrical engineer
0
X

new posts
Back
to top
Latest

Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

Poll

Join the discussion

How are you feeling about your results?

They're better than I expected (144)
40.45%
They're exactly what I expected (87)
24.44%
They're lower than I expected (125)
35.11%