OHM' s Law, Ohmic & Non-Ohmic devices | Ch 16 CURRENT ELECTRICITY| Physics 10 | Lec 3 | NBF | FBISE

Ohm's Law Fundamentals
📌 Ohm's Law, attributed to Simon Ohm, provides the foundational structure for current electricity, comparable in importance to Newton's laws in mechanics.
⚡ The flow of conventional electric current in a circuit is entirely due to the potential difference (voltage) across the conductor; if the potential difference is zero, no current flows.
🔗 Ohm stated that the voltage (energy per unit charge) is directly proportional to the current (charge flow per unit time), meaning increasing voltage increases current, and vice versa.

Derivation and Resistance
➗ When the proportionality sign is removed, it introduces the constant of proportionality, R (Resistance), leading to the relationship $V = IR$, or $R = \frac{V}{I}$.
🛑 Resistance (R) is the opposition encountered by charges as they move through the conductor, caused by collisions with atoms and molecules, leading to energy loss.
➗ The unit of resistance is the Ohm ($\Omega$), defined as one Volt per Ampere ($\text{V/A}$), named after Ohm.

Conditions for Ohm's Law Applicability
🌡️ Ohm's Law is only strictly applicable when Resistance (R) remains constant, which requires two primary conditions:
1. The temperature of the conductor must remain constant; increased temperature causes faster atomic vibrations, increasing resistance.
2. The physical state of the material must remain unchanged (e.g., not compressing the conductor or altering its dimensions like length or cross-sectional area).
📈 When these conditions are met, the V-I graph results in a perfectly straight line, confirming direct proportionality.

Ohmic vs. Non-Ohmic Bodies
🟢 Ohmic devices strictly follow Ohm's Law, exhibiting a straight-line V-I graph because their resistance is constant under constant temperature and physical state (e.g., good metallic conductors like Copper or Silver).
🔴 Non-Ohmic devices do not follow Ohm's Law, meaning their V-I graph is curved, as their resistance changes with variations in voltage/current (e.g., due to heating effects).
💡 Examples of non-Ohmic devices include the filament of a bulb, where current turns into heat, increasing resistance significantly, and semiconductors, where increased heat can break covalent bonds, releasing more free electrons and drastically changing current flow for small voltage changes.

Key Points & Insights
➡️ The core principle of Ohm's Law is the direct proportionality between Voltage (V) and Current (I), provided resistance R is constant.
➡️ Resistance increases if the conductor's temperature rises due to collisions, causing the current to decrease relative to the applied voltage.
➡️ For a V-I graph to confirm Ohm's Law, it must be a straight line, indicating that resistance does not change across the operating range.
➡️ Ohmic devices maintain constant resistance, whereas Non-Ohmic devices (like bulb filaments or semiconductors) show resistance that varies, often due to thermal effects.

📸 Video summarized with SummaryTube.com on Oct 15, 2025, 12:54 UTC