# Electricity: Resistance

## Electricity: Resistance

• “Resistance” in the context of electricity refers to the opposition or hindrance to the flow of electrical current through a conductor.

• The unit of resistance is the Ohm (Ω).

• Resistance in a conductor is fundamentally caused due to collisions between moving electrons (electric current) and the fixed particles of the conductor.

• Ohm’s Law states that the current flowing through a conductor is directly proportional to the voltage across it, provided that the temperature remains constant. Mathematically, this can be represented as V=IR, where V is the voltage, I is the current and R is the resistance.

• Resistance depends on several factors including the nature of the material, the length and cross-sectional area of the conductor, and the temperature.

• Metals or conductive materials have a lower resistance compared to insulators. This is because metals have a large number of free electrons that can move and carry a current.

• The longer the conductor, the higher the resistance as there are more collisions of electrons with the fixed particles of the conductor.

• A larger cross-sectional area of a conductor will reduce the resistance as there is more space for electrons to move, resulting in fewer collisions.

• Temperature affects resistance as when a conductor heats up, the particles vibrate more which leads to an increased number of collisions, and therefore increased resistance.

• Resistances in a series add up. If there are 2 resistors in a series with resistances R1 and R2, the total resistance, Rt = R1 + R2

• For resistances in parallel, 1 over the total resistance equals the sum of the reciprocals of the individual resistances. 1/Rt = 1/R1 + 1/R2.

• The electrical power consumed by a resistor can be derived from the formula P=I^2 R or P=V^2 / R where P is power, I is current, V is voltage and R is resistance.

Remember to understand, memorise and frequently practise problems based on these key points as they are crucial in understanding and applying the concept of resistance.