Semiconductor Temperature Dependence
Semiconductors generally have a negative temperature coefficient over the elementary regime. Their resistance can vary nonlinearly, often with activated behavior, so the metal linear law is not automatically valid.
Why this shows up in the exam
Thermistors · Comparing metal and semiconductor cooling · Interpreting nonlinear R-temperature plots
Learn the idea
Semiconductor resistance commonly falls with temperature because carrier generation dominates. Heating a semiconductor frees many more charge carriers. Although collisions also increase, the rapid carrier-number increase usually raises conductivity and lowers resistance.
🧠 Memory hook: Metals usually get harder to conduct; semiconductors gain carriers.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- R decreases as T increases — qualitative semiconductor trend in the standard regime
- sigma = n |q| mu — carrier density and mobility jointly control conductivity
How to approach it
- 1Identify the material class
- 2Track both n and mobility
- 3Use the graph or model actually supplied
Common slip-ups that cost marks
- •Applying a metal's positive alpha to a semiconductor
- •Attributing the trend only to mobility
- •Assuming a straight R-T line without evidence
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A cell of emf 6 V and internal resistance 1 ohm is connected to a 2 ohm resistor. Find the circuit current.
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