# Applying mutiple resistors to create an 18k

• Megasundato
In summary, an 18k resistor is a standard value and can be found in decade multiples of 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.25%.
Megasundato
Hello. my robot requires an 18k resistor at one point. my problem is that I don't have one and my radioshack has never heard of it.

anyway, I was wondering on how to create one. I know that adding in a series circuit it's just R1+R2... and I think that parallel circuits add with the reciprocal.

so how can one get an 18k. Someone told me that I could make a parallel circuit with a 22k and some 1ks, but I don't think that would work. I know that I could create one in a serial circuit, but that might take a lot of resistors.

thanks for the help.

18k is very much a standard value. In higher tolerance parts many more values may be available, but even the most basic 10% parts should be available in decade multiples of the following.

1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2

5% resistors follow the E24 series: there are 24 resistor values in a decade. That's fancy speak for there being 24 logarithmically-spaced values from 10 to 91 ohms (and 24 from 100 to 910 and so forth).

You can calculate the value of two parallel resistances as follows:
$$\frac{1}{R_{parallel}}=\left(\frac{1}{R_{1}}+\frac{1}{R_{2}}\right)$$ or
$$R_{parallel}=\left(\frac{1}{R_{1}}+\frac{1}{R_{2}}\right)^{-1}$$

Three resistors in parallel add the same way:
$$\frac{1}{R_{parallel}}=\left(\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}}\right)$$

A handy thing to remember is that two equal resistors in parallel have an equivalent resistance of half their value (three in parallel having a third, and so on). So if you don't have an 18k, you can put two 36k resistors in parallel (which should be more plentiful--hit search to do the calculation):

5% resistors follow the E24 series: there are 24 resistor values in a decade.
Yep, and both the E12 and the E24 series include 18k. So it's pretty hard to believe that radioshack has never heard of it.

uart said:
Yep, and both the E12 and the E24 series include 18k. So it's pretty hard to believe that radioshack has never heard of it.

Maybe the sales guy was just trying to sell some batteries or an extended warranty?

In any case, to the OP, I recommend finding a real electronics supply / hobby shop in your area (assuming one still exists).

thanks for your help. I see how I can do this now.

## 1. How do you calculate the resistance of multiple resistors in a circuit?

The total resistance of multiple resistors in a circuit can be calculated using the formula R = R1 + R2 + R3 + ..., where R1, R2, R3, etc. are the individual resistances of each resistor. This is known as the series circuit.

## 2. How do you create an 18k resistance using multiple resistors?

To create an 18k resistance, you can use two 9k resistors in series. The total resistance will then be 18k (9k + 9k). Alternatively, you can use three 6k resistors in parallel. The total resistance in this case will also be 18k (1/(1/6k + 1/6k + 1/6k)).

## 3. What is the difference between series and parallel circuits?

In a series circuit, the resistors are connected in a single path, so the current flowing through each resistor is the same. In a parallel circuit, the resistors are connected in multiple paths, so the voltage across each resistor is the same. Additionally, the total resistance in a series circuit is equal to the sum of the individual resistances, while the total resistance in a parallel circuit is less than the smallest individual resistance.

## 4. Can you mix resistors with different values in a circuit?

Yes, you can mix resistors with different values in a circuit. This can be useful if you need a specific resistance that cannot be achieved with a single resistor.

## 5. How do you determine the power dissipation of a circuit with multiple resistors?

The power dissipation of a circuit with multiple resistors can be determined using the formula P = I2R, where I is the current flowing through the circuit and R is the total resistance. If the current is not given, you can use the formula P = V2/R, where V is the voltage across the circuit.

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