Definition of Resistance:

• Resistance is a measure of how much a resistor opposes the flow of electric current. It is denoted by the symbol R and measured in ohms (Ω).

Ohm’s Law:

• The relationship between voltage (V), current (I), and resistance (R) is given by Ohm’s Law:

V = IR

• This law helps calculate the resistance when the voltage and current in the circuit are known.

Series Combination of Resistors:

• When resistors are connected end-to-end, they are said to be in series.
• The total or equivalent resistance (R_eq​) of resistors in series is the sum of the individual resistances:

R_eq = R1 + R2 + R3 + …

• The current through each resistor is the same, but the voltage across each resistor is different.

Parallel Combination of Resistors:

• When resistors are connected such that they share the same two nodes, they are in parallel.
• The reciprocal of the total or equivalent resistance (R_eq​) for resistors in parallel is the sum of the reciprocals of the individual resistances:

1/R_eq = 1/R1 + 1/R2 + 1/R3 + …

• The voltage across each resistor is the same, but the current through each resistor is different.

Combination of Series and Parallel Resistors:

• In practical circuits, resistors can be arranged in combinations of series and parallel.
• To calculate the total resistance, first simplify the parallel and series parts step-by-step, reducing the circuit to an equivalent resistance.

Resistances in Everyday Applications:

• Resistors are used in electronic devices to control the current and voltage levels, ensuring safe operation of components like LEDs and transistors.

Factors Affecting Resistance:

Resistance of a conductor depends on:

• Material: Different materials have different resistivity.
• Length: Resistance is directly proportional to the length of the conductor.
• Cross-sectional Area: Resistance is inversely proportional to the cross-sectional area.
• Temperature: Resistance usually increases with an increase in temperature.

Resistor Color Code:

• Resistors are labeled with a color code to indicate their resistance value. Understanding how to read this code is important for identifying resistances in circuits.

Let’s practice!