How to Change the Resistance of a Resistor With Another Resistor

Sometimes you need a resistor with a value you don't have in your kit. Instead of ordering and wanting for a resistor with a value you need you can change the resistance of a resistor by using another resistor or many. By installing resistors in a parallel or series circuit you can change the value in Ohms.

Parts:

1. You will need a few resistors
2. Multimeter
3. Breadboard

Here is a link to a resistor calculator.

Step 1: Resistors in Parallel.

Resistor in parallel:

Using the calculator

100 Ohm resistor in a parallel circuit with a 100 Ohm resistor you give you a total resistance of 50 Ohm's

470 Ohm resistor in a parallel circuit with a 470 Ohm resistor you give you a total resistance of 235 Ohm's

The two resistors don't need to have the same value. You can also use two resistors with a different value.

100 Ohm resistor in a parallel circuit with a 50 Ohm resistor you give you a total resistance of 33.33 Ohm's

100 Ohm resistor in a parallel circuit with a 25 Ohm resistor you give you a total resistance of 20 Ohm's

You can also use more then two resistors.

100 Ohm resistor in a parallel circuit with a 25 Ohm resistor and a 25 Ohm resistor you give you a total resistance of 11.11 Ohm's

100 Ohm resistor in a parallel circuit with a 25 Ohm resistor and a 20
Ohm resistor you give you a total resistance of 10 Ohm's

Step 2: Resistors in Series.

Resistor in series:
Using the calculator

100 Ohm resistor in a series circuit with a 100 Ohm resistor you give you a total resistance of 200 Ohm's

470 Ohm resistor in a series circuit with a 470 Ohm resistor you give you a total resistance of 940 Ohm's

The two resistors don't need to have the same value. You can also use two resistors with a different value.

100 Ohm resistor in a series circuit with a 50 Ohm resistor you give you a total resistance of 150 Ohm's

100 Ohm resistor in a series circuit with a 25 Ohm resistor you give you a total resistance of 125 Ohm's

You can also use more then two resistors.

100 Ohm resistor in a series circuit with a 25 Ohm resistor and a 25 Ohm resistor you give you a total resistance of 150 Ohm's

100 Ohm resistor in a series circuit with a 25 Ohm resistor and a 20 Ohm resistor you give you a total resistance of 145 Ohm's

Step 3: Resistors in Parallel and Series.

I don't have a calculator for this how ever you can use the same calculator as before.

Parallel circuit you have a 20 Ohm resistor and a 20 Ohm resistor with a total resistance of 10 Ohm's

Your parallel circuit is in series with a 100 Ohm resistor giving you a total resistance of 110 Ohm's.

Same as above but now your adding another resistor in the series circuit.

Parallel circuit you have a 20 Ohm resistor and a 20 Ohm resistor with a total resistance of 10 Ohm's
Your parallel circuit is in series with a 100 Ohm resistor and 100 Ohm resistor giving you a total resistance of 210 Ohm's.

Step 4: Ohm's Law

Ohm's law defines a linear relationship between the voltage and the current in an electrical circuit.

The resistor's voltage drop and resistance set the DC current flow through the resistor.

With water flow analogy we can imagine the electric current as water current through pipe, the resistor as a thin pipe that limits the water flow, the voltage as height difference of the water that enables the water flow.

R=Resistance(Ω)

I=Amps

V= Volts

Ohm's law definition
The resistor's current I in amps (I) is equal to the resistor's voltage VR=V in volts (V) divided by the resistance 9R) in ohms (Ω):

I=V/R (Amps=Volts/Resistance)

Voltage calculation:
When we know the current and resistance, we can calculate the voltage.

The voltage V in volts (V) is equal to the to the current I in amps (I) times the resistance (R) in ohms (Ω):

V=I*R (volts=Amps*Resistance)

Resistance calculation:
When we know the voltage and the current, we can calculate the resistance.

The resistance (R) in ohms (Ω) is equal to the voltage in volts (V) divided by the current I in amps (I):

R=V/I (Resistance=Volta/Amps)

Since the current is set by the values of the voltage and resistance, the Ohm's law formula can show that:

• If we increase the voltage, the current will increase.
• If we increase the resistance, the current will reduce.