Circuits - Calculating Effectice Resistance

In summary, the 12,4,16 Ohm resistors in the top branch are in parrallel and have an effective resistance of 3.88Ω.
  • #1
FaraDazed
347
2
Sorry for my crude drawings but I thought it was easiest and quickest this way to post the question.

Homework Statement



Calculate the effective resistance for the circuits below.

A.
circuit_A.jpg


B:
circuit_B.jpg



Homework Equations


[tex] R_{series}=\sum\limits_{i=1}^n R_i \\
\frac{1}{R_{parallel}}=\sum\limits_{i=1}^n \frac{1}{R_i}
[/tex]


The Attempt at a Solution



We have never been told how to calculate the effective resistance where both series and parallel occur, only how to do it if it is series and how to do it if it is parallel. But using intuition for part A i just did the bit in series and then the bit in parallel and added them like below.

[tex]
\sum\limits_{i=1}^n R_i = 2+2=4 \\
\sum\limits_{i=1}^n \frac{1}{R_i} = \frac{1}{2}+\frac{1}{2} = 1 ∴ R=1 \\
∴R_{total}=4+1=5Ω
[/tex]

For part B I am scratching my head as to where to start because the whole thing is in parallel and then there are parrellel bits inside of that iyswim. Any hints on how to approach part B would be much appreciated, thanks.
 
Last edited:
Physics news on Phys.org
  • #2
Forget about the rest of the circuit .First consider only 12,4,16 Ohm resistors in the top branch .What do you think ? Are they in series or parallel ? Can you calculate their effective resistance ?
 
Last edited:
  • Like
Likes 1 person
  • #3
Tanya Sharma said:
Forget about the rest of the circuit .First consider only 12,4,16 Ohm resistors in the top branch .What do you think ? Are they in series or parallel ? Can you calculate their effective resistance ?

Right ok, I think I see what your getting at. So as the 12,4 and 16 are in parrallel I can calculate the effective resistance of just that, ignoring the rest (for now), and replace the 12,4,16 branches with the effective resistance. Ok I will have a go now.
 
  • #4
Yes...that is correct .
 
  • Like
Likes 1 person
  • #5
OK so for part B then I broke it down to the individual branches to make it easier on the eye.

Top Branch:
[tex]
3+9+(\frac{1}{12}+\frac{1}{4}+\frac{1}{16})^{-1}=14.53Ω[/tex]

Middle Branch[tex]
20+10=30Ω[/tex]

Bottom Branch[tex]
5+(\frac{1}{8}+\frac{1}{33})^{-1}=6.44Ω[/tex]

Putting it all together[tex]
(\frac{1}{14.53}+\frac{1}{30}+\frac{1}{6.44})^{-1}=3.88Ω
[/tex]
 
  • #6
Nice work :thumbs:
 
  • Like
Likes 1 person
  • #7
Thanks for your help :)
 
  • #8
You are welcome :smile:
 
  • Like
Likes 1 person

FAQ: Circuits - Calculating Effectice Resistance

What is effective resistance?

Effective resistance, also known as total resistance, is the overall resistance in a circuit that determines how much current will flow through the circuit. It is calculated by adding the individual resistances in a series circuit or by using the formula for parallel circuits.

How do you calculate effective resistance in a series circuit?

In a series circuit, the effective resistance is simply the sum of all the individual resistances. This means that you add up all the resistances in the circuit to get the total or effective resistance.

How do you calculate effective resistance in a parallel circuit?

In a parallel circuit, the effective resistance is calculated using the following formula: 1/Reff = 1/R1 + 1/R2 + ... + 1/Rn, where Reff is the effective resistance and R1, R2, etc. are the individual resistances in the circuit. Then, to get the effective resistance, you take the reciprocal of the sum of the reciprocals.

How does adding resistors in series affect effective resistance?

When resistors are added in series, the effective resistance increases. This is because the total resistance in a series circuit is equal to the sum of all the individual resistances. So, as more resistors are added, the total resistance increases.

How does adding resistors in parallel affect effective resistance?

When resistors are added in parallel, the effective resistance decreases. This is because the total resistance in a parallel circuit is less than the smallest individual resistance. So, as more resistors are added, the total resistance decreases.

Similar threads

Back
Top