Practical Examples
Example 1: LED String
We have four LEDs that are connected in series. Each LED has a forward voltage drop of 3V and operates at 20mA. Calculate the appropriate resistor value to limit the current.
Solution:
Total Voltage Drop = 4 LEDs * 3V/LED
= 12V
Remaining Voltage (VR) = Applied Voltage – Total Voltage Drop
= 12V – 12V = 0V
Resistor Value (R) = VR / I
= 0V / 0.020A
= 0Ω
In this case, a resistor with a value of 0Ω is needed to limit the current to 20mA, but since resistors cannot have zero resistance, a practical approach would be to use the nearest standard resistor value, such as 1Ω.
Example 2: Battery Life
Consider a series circuit powered by a 9V battery with three resistors connected in series. The resistors have values of 220Ω, 330Ω, and 470Ω. Calculate the total resistance and the current flowing through the circuit.
Total Resistance (RT) = R1 + R2 + R3
= 220Ω + 330Ω + 470Ω
= 1020ΩTotal Current (I) = V / RT
= 9V / 1020Ω
≈ 0.00882A or 8.82mA
Resistors in Series
Resistors are devices that obstruct the flow of electric current in the circuit. They provide the hindrance to the path of the current which flows in the circuit.
A resistor is a two-terminal electrical component that works by reducing the flow of charge and voltage levels in the circuit. Most of the circuits have one or more resistors to oppose the flow of current and balance the circuit. Most commonly there are two combinations of resistors – Resistors in Series and Parallel.
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