• Resistance of a material isn’t just about its composition but also its size and shape.

Fun Fact: Think of a guitar string. A thicker string sounds different than a thin one. Just like in electricity, thicker conductors (or wires) have less resistance!

• Resistance (R) is proportional to its length (L) ⇒ ∝R∝L
• Resistance (R) is inversely proportional to its cross-sectional area (A) ⇒ ∝1R∝\(\frac 1A\)​
• So, combining the two: ∝R∝AL​

• Resistivity (ρ) is like the "personality" of a material, defining its natural resistance.
• It's defined as ρ = \(\frac {R× A}{L}\)
• Unit: ohm-metre (Ωm)

Real-World Analogy 🍩🎈
Imagine you're trying to blow up a balloon (resistance) through different sizes of straws (conductors). A thin, long straw is harder (more resistance) than a short, wide one. But regardless of the straw's shape or size, if they're all made of the same material, they have the same "resistivity".

• Resistivity (ρ) is consistent for pure samples of a material, independent of its shape or size.
• It's similar to how density or specific latent heat are constant for a material.

• Example 9: For a wire with a radius of 0.16mm and length of 7.5m, its resistance with a given resistivity is 65Ω.
• Example 10: A copper block with specified dimensions has a resistance of 0.023mΩ.