9.3 Resistance and resistivity

Define resistance.

Resistance is a measure of how much a component resists the flow of current. It is measured in ohms (Ω) and depends on the material, temperature, and dimensions of the conductor.

State Ohm’s Law.

Ohm’s Law states that the potential difference across a conductor is directly proportional to the current through it, provided temperature remains constant.
V = IR.

Describe the I–V characteristic of a metallic conductor.

For a metallic conductor, current increases linearly with potential difference at constant temperature, giving a straight-line I–V graph through the origin.

Describe the I–V characteristic of a semiconductor diode.

A semiconductor diode has a non-linear relationship between current and potential difference. The current increases rapidly after a certain threshold voltage is reached,  and the I-V graph is exponential.

Describe the I–V characteristic of a filament lamp.

The resistance of a filament lamp increases with temperature as current flows through it. This results in a non-linear I-V graph, where the current increases less sharply as the voltage increases.

Describe and explain the effect of temperature on the resistance of a filament lamp.

As the current increases, the temperature increases, so there is less resistance. This is due to increases vibrations of atoms in the filament, which impede the flow of electrons more as the temperature increases.

State the formula for the resistance of a uniform conductor.

R = pL/A

where R = resistance (Ω), p = resistivity (Ωm), L = length (m), A = cross-sectional area (m²).

Explain how the resistance of a light-dependent resistor (LDR) changes with light intensity.

An LDR is a resistance decreases as light intensity increases. In bright light, the resistance is low, and in the darkness, the resistance is high.

Explain how the resistance of a thermistor changes with temperature.

A thermistor is a type of resistor whose resistance decreases as temperature increases. Thermistor have a negative temperature coefficient, meaning their resistance decreases as the temperature rises.