# Calculate the equivalent resistance

• Sylvia
In summary, when calculating the equivalent resistance of a circuit, it is important to first determine if the resistors are in series or parallel. In this case, the 7.1 ohm and 5.8 ohm resistors are in series, so they must be added together before being added in parallel to the 3.2 ohm resistor. This results in a total equivalent resistance of 7.1 + 5.8 + (1/((1/3.2) + (1/4.5))) = 7.1 + 5.8 + 1.82 = 14.72 ohms.
Sylvia

## Homework Statement

Ignore the internal resistance of the battery and assume it is merely a battery. Calculate the equivalent resistance of the circuit.

## Homework Equations

1/Req = 1/R + 1/R ... (parallel)
Req = R + R ... (series)

## The Attempt at a Solution

I know this is fairly simple but I don't understand how you would calculate the equivalent resistance for the three resistors (3.2 ohms, 7.1 ohms, 5.8 ohms). I assumed they were in series and simply added them, and then added 1.0 ohms and 4.5 ohms to get the total resistance. I think this is wrong, can someone explain how you would go about calculating the Req?

Sylvia said:

## Homework Statement

Ignore the internal resistance of the battery and assume it is merely a battery. Calculate the equivalent resistance of the circuit.

## Homework Equations

1/Req = 1/R + 1/R ... (parallel)
Req = R + R ... (series)

## The Attempt at a Solution

I know this is fairly simple but I don't understand how you would calculate the equivalent resistance for the three resistors (3.2 ohms, 7.1 ohms, 5.8 ohms). I assumed they were in series and simply added them, and then added 1.0 ohms and 4.5 ohms to get the total resistance. I think this is wrong, can someone explain how you would go about calculating the Req?

I'm afraid you're wrong. All of them aren't in series. See the figure I've uploaded. What can you infer from that? Always deal with 2 resistances at a time. Don't involve 3 together.

#### Attachments

• resistance.JPG
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I see what you are saying, since 7.1 and 5.8 are in series, they must be added together? And then added in parallel to 3.2?

Sylvia said:
I see what you are saying, since 7.1 and 5.8 are in series, they must be added together? And then added in parallel to 3.2?
You got that right mate!

thanks!

Sylvia said:
thanks![/QUOT

## 1. What is equivalent resistance?

Equivalent resistance is the single resistance value that represents the combined effect of multiple resistors in a circuit. It is calculated by replacing the resistors with a single resistor that would have the same effect on the circuit.

## 2. How do you calculate equivalent resistance for resistors in series?

To calculate equivalent resistance for resistors in series, simply add the resistance values of each individual resistor together. The total resistance will be the sum of all the resistors.

## 3. How do you calculate equivalent resistance for resistors in parallel?

To calculate equivalent resistance for resistors in parallel, use the formula 1/Req = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn, where Req is the equivalent resistance and R1, R2, R3, etc. are the individual resistances. Then, take the reciprocal of the sum to get the equivalent resistance.

## 4. How does adding resistors in series affect the equivalent resistance?

When resistors are added in series, the equivalent resistance increases. This is because the current has to pass through each resistor, resulting in a larger overall resistance.

## 5. How does adding resistors in parallel affect the equivalent resistance?

When resistors are added in parallel, the equivalent resistance decreases. This is because the current has multiple paths to flow through, resulting in a smaller overall resistance.

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