Equivalent resistance of circuit

In summary, the problem is to find the equivalent resistance between terminals A and B in a circuit with four resistors (20 ohm, 30 ohm, 60 ohm, and 40 ohm). The student knows how to add resistances in parallel and series, but is unsure which ones are connected in each. It appears that the 20 ohm and 30 ohm resistors are in series, as well as the 60 ohm and 40 ohm resistors. However, the student is still unsure of where to place the equivalent resistances. The key is to treat the endpoints of a zero resistance wire as the same point, creating a figure-of-eight with "a" in the middle. This
  • #1
Learnphysics
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0

Homework Statement



Find the equivalent resistance between terminals A and B for this circuit:

http://img716.imageshack.us/img716/1121/1035p.png

[PLAIN]http://img716.imageshack.us/img716/1121/1035p.png

Homework Equations



I know how to add resistances in parralell and series, it's just that i can't figure out which ones are connected in parralell and which ones are in series


The Attempt at a Solution



It kind of appears that the 20 ohm and 30 ohm resistors are in series, and that 60 ohm and 40 ohm resistors are in series.

But i have no idea.

A parralell connection is one which has both ends of an element directly connected to another. This appears to be true for the 20 and 30 ohm resistors. And also for the 60 and 40 ohm resistors. But where in the circuit would i place their equivlent resistances?

So i guess the question I'm asking is more to do with how to identify which ones are parralell and which ones are in series
 
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  • #2
Hi Learnphysics! :smile:

With a wire of zero resistance, you can ignore the wire and treat the two endpoints as the same point …

in this case, that makes a sort of figure-of-eight with "a" in the middle …

that should make it clear :wink:​
 
  • #3
tiny-tim said:
Hi Learnphysics! :smile:

With a wire of zero resistance, you can ignore the wire and treat the two endpoints as the same point …

in this case, that makes a sort of figure-of-eight with "a" in the middle …

that should make it clear :wink:​

Thank you!

The equivalent resistance i got is 9.6 ohms which seems to work out.
 
  • #4
Learnphysics said:
9.6 ohms
Looks good to me.
 
  • #5
Sry but i still don't get it..mind to explain in more detail(how to know they are parallel or series to each other)?
 

FAQ: Equivalent resistance of circuit

1. What is equivalent resistance in a circuit?

Equivalent resistance in a circuit refers to the total resistance that a current encounters when flowing through a circuit. It is calculated by combining all of the resistances in a circuit into a single resistance value.

2. How do you calculate equivalent resistance in a series circuit?

In a series circuit, equivalent resistance is calculated by simply adding up all of the individual resistances in the circuit. This is because the current encounters each resistance one after the other, so the total resistance is the sum of all resistances.

3. How do you calculate equivalent resistance in a parallel circuit?

In a parallel circuit, equivalent resistance is calculated using the formula 1/Req = 1/R1 + 1/R2 + 1/R3 + ... where Req is the equivalent resistance and R1, R2, R3, etc. are the individual resistances. This is because the current has multiple paths to take, so the total resistance is less than any single resistance.

4. Why is equivalent resistance important in circuit analysis?

Equivalent resistance is important in circuit analysis because it allows us to simplify complex circuits and analyze their behavior using basic Ohm's law equations. It also helps us understand how much current will flow through a circuit and how much voltage will be dropped across each component.

5. How does the addition of resistors affect equivalent resistance in a circuit?

Adding resistors in series will increase the equivalent resistance, as the current has to flow through each resistor, increasing the overall resistance. In contrast, adding resistors in parallel will decrease the equivalent resistance, as the current is split between multiple paths, reducing the overall resistance.

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