Resistors/Resistance
A Resistance is the opposition to a flow of electric current through a circuit. It is a measure of how hard it is to push electricity through a circuit. It is measured in ohms. Factors that affect resistance are thickness, material, length, and temperature. There are two types of Resistance formulas that correspond with Series and Parallel Circuits, which are explained below.
Resistance in Series Circuits
- total resistance increases
- total current decreases
- Formula: R = R1 + R2 + R3 + ...
Resistance in Parallel Circuits
- total resistance decreases
- total current increases
- Formula: 1 / R = 1 / R1 + 1 / R2 + 1 / R3 + ...
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 V in volts (V) divided by the current I in amps (A).
Since the current is set by the values of the voltage and resistance, the Ohm's law formula can show that:
Example: What is the resistance of an electric frying pan that draws 12 amps of current when connected to a circuit with 144 volts?
R= V/I R = 144v/12a = 12 ohms
The resistance R in ohms (Ω) is equal to the voltage V in volts (V) divided by the current I in amps (A).
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.
Example: What is the resistance of an electric frying pan that draws 12 amps of current when connected to a circuit with 144 volts?
R= V/I R = 144v/12a = 12 ohms