Why Ohm’s Law Sometimes Fails ⚡

Ohm’s law says \(V = IR\), meaning voltage V is directly proportional to current I through resistance R. But some materials and devices don’t follow this simple link. Here’s how the mismatch usually shows up: 🎢:contentReference[oaicite:0]{index=0}

  1. Non-linear curve – The graph of V vs. I bends instead of staying straight. As current rises, voltage doesn’t keep pace in a steady ratio. (Think of the solid line curving away from the dashed straight line on the graph.)
    Tip: Metal filaments at high temperature or semiconductors near breakdown behave this way. 💡:contentReference[oaicite:1]{index=1}
  2. Direction matters – Flipping the voltage sign doesn’t mirror the current. A diode is the classic example: it lets current flow easily one way but hardly at all the other way. ➡️⛔:contentReference[oaicite:2]{index=2}
  3. Multiple voltages for one current – For some materials (like GaAs), a single current value can pair with more than one voltage. The V–I curve loops back on itself, giving several operating points. 🔄:contentReference[oaicite:3]{index=3}

Engineers actually rely on these “rule-breakers” to build rectifiers, switches, and oscillators. So, while Ohm’s law is super useful, knowing its limits unlocks a wider world of electronics! 🚀:contentReference[oaicite:4]{index=4}

🎯 High-Yield NEET Pointers

  • Spot non-ohmic graphs: Identify curved V–I plots versus straight-line ohmic plots.
  • Rectifier action: Remember that a diode’s one-way conduction breaks the V–I symmetry.
  • GaAs quirk: Multiple voltages for one current hint at negative resistance regions—often asked in concept questions.
  • Comparison skill: Be ready to match devices (filament lamp, diode, transistor) to their characteristic curves.