# How to find the equivalent Resistance of these circuits

• Aafour
In summary, to find the equivalent resistance of these circuits, we use the formula 1/Req = 1/(R1 + R2) + 1/R3. For the given example, with two resistors (r1 and r2) connected in parallel with an equivalent resistance of 10/3 ohms, the current divides in the ratio of 2 to 1. By substituting the value of voltage (V) into the equations I = V/r1 and 2I = V/r2, we can find the individual resistances of r1 and r2.
Aafour
Suppose that all resistors have a value of 100 ohm

how to find the equivalent Resistance of these circuits, the number in these circuits indicate the areas for which we will be completing calculations.

how to go over thesehttp://img155.imageshack.us/img155/8421/32990280.jpg

http://img24.imageshack.us/img24/6659/20062468.jpg

http://img69.imageshack.us/img69/453/10031901.jpg

thanks

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Do you know how to find the equivalent resistance of series and parallel combination of resistances?

rl.bhat, yes i know how to find series and parallel combination of resistances,

for series just add the resistances, and for parallel, (1/R)=(1/R1)+(1/R2)+...

but I really don't know how to start on these circuits listed

OK. In the case 1, two resistances are in series and this combination is in parallel with the third resistance.
So 1/Req = 1/(R1 + R2) + 1/R3.
In the same way try the other combination.

true, thank you. it's just that i need to draw these circuits in more easy way. thank you

Hey! what about if i have the value of the equivalent resistance and want to work out the value of the 2 resistors that were previously there? cheers

Sorry. I didn't understand your question. Give a numerical example.

ok
Two resistors r1 and r2 connected in parallel have an equivalent resistance of 10/3 ohms.
When the current enters the parralell circuit it divides between the two resistors in the ratio of 2 to 1. Determine r1 and r2?
hope u can help :)

If 3I current flows through the parallel combination, in r1 the current is i and in r2 the the current is I2.
The voltage across the parallel combination is V = 3I*10/3 = 10*I
So the current in r1 = I = V/r1
The current in r2 = 2I = V/r2
Substitute the value of V and find r1 and r2.

## 1. What is resistance and why is it important in circuits?

Resistance is the measure of how much a material or component impedes the flow of electric current. In circuits, resistance plays a crucial role in determining the amount of current that can flow through a circuit and how much voltage is required to produce that current. It also helps in controlling the flow of electricity and protects components from getting damaged due to excessive current.

## 2. How can I calculate the equivalent resistance of a series circuit?

In a series circuit, the equivalent resistance is the sum of individual resistances. This means you can simply add up the values of all the resistors in the circuit to find the total resistance. The formula for calculating equivalent resistance in a series circuit is R = R1 + R2 + R3 ...

## 3. What is the formula for calculating equivalent resistance in a parallel circuit?

In a parallel circuit, the equivalent resistance is less than the smallest individual resistance. The formula for calculating equivalent resistance in a parallel circuit is 1/R = 1/R1 + 1/R2 + 1/R3 ... Once you have calculated the reciprocal of the sum, take the reciprocal again to get the equivalent resistance.

## 4. Can I use Ohm's Law to find the equivalent resistance of a circuit?

Yes, Ohm's Law (V = IR) can be used to find the equivalent resistance of a circuit. You can rearrange the formula to R = V/I, where V is the voltage across the circuit and I is the current flowing through it. However, this method is only applicable for series circuits.

## 5. How do I find the equivalent resistance of a complex circuit with both series and parallel components?

To find the equivalent resistance of a complex circuit, you can simplify the circuit by breaking it down into smaller parts and then finding the equivalent resistance of each part using the methods mentioned above. Once you have found the equivalent resistance of each part, you can use the series and parallel formulas to find the total equivalent resistance of the circuit.

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