42. Physics Electric Resistance

🔢 Ohm’s Law (Key Formula)

Ohm’s Law is a fundamental relationship between:

V – Voltage (electric potential difference)

I – Current (flow of electric charge)

R – Resistance

The law is:

𝑉
=
𝐼
×
𝑅
V=I×R

Or rearranged:

𝑅
=
𝑉
𝐼
R=
I
V



This means the resistance is how much voltage is needed to push a certain amount of current.
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📏 Unit of Resistance

The SI unit of resistance is the ohm (Ω).
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🧠 How Resistance Depends on the Material

Resistance (R) of a wire depends on:

Material — Materials with more free electrons (like copper) have lower resistance.
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Length (L) — Longer wires cause more collisions, so more resistance.
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Cross-section (Area A) — Thicker wires let electrons flow easier, so less resistance.
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Mathematically:

𝑅
=
𝜌
𝐿
𝐴
R=ρ
A
L



Where ρ (rho) is the resistivity of the material — a property that tells how strongly the material resists current.
BYJU'S

🔥 Resistance & Heat (Joule Heating)

As electrons scatter in a resistor, electrical energy is converted to heat — that’s called Joule heating. This is why devices like heater coils and toasters get hot: they are made to have high resistance to convert electricity to heat.
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📉 Effects of Resistance in a Circuit

More resistance → less current for the same voltage.
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Adding resistance (like extra wire or bulbs) dim lights or reduce current flow.