Resistance

The resistance of a component is the ratio of the potential difference across the component to the current flowing through it.

S.I Unit: ohm (\Omega)

Formula:

resistance = \frac{potential \space difference}{current} \space or \space R = \frac{V}{I}

• Resistance is used to control the amount of current flowing through any device

Series

• The effective resistance, R, of resistors connected in series can be caluclated by adding the resistance of individual resistors.

Parallel

• Effective resistance of resistors connected in parallel is calculated using the following formula:

\frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \space or \space R = \frac{1}{\frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}}

Factors Affecting Resistance

• Temperature
• Length
• Cross-sectional area

Formula:

R = \frac{\rho l}{A}

• R = resistance of wire
• \rho = resistivity of wire in \Omegam
• l = length of wire
• A = cross-sectional area