Resistivity as temperature changes
"Resistivity as temperature changes" is a free, interactive Class 12 Physics simulation for NEET and JEE, built on the NCERT section "Resistivity of materials and its temperature dependence" in Current Electricity. Resistivity against temperature for copper, manganin and silicon, with meters for carrier density n and relaxation time τ explaining each slope. NEET has asked about this idea 5 times in 10 years of papers. JEE Main asked 65 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Resistivity of materials and its temperature dependence in Current Electricity. Change the values and watch what happens.
What it shows
NCERT § Temperature Dependence of Resistivity
Resistivity against temperature for copper, manganin and silicon, with meters for carrier density n and relaxation time τ explaining each slope.
Controls
3 to try
- Slidertemperature −50 to 400 °C
- Segmentedcopper / manganin / silicon
- Togglelog scale
Try this
Find the material whose resistance changes by less than 1% from 20 °C to 100 °C, and the one whose resistance falls on heating.
Common mistake
Explaining the rise of a metal's resistance by a change in n (it is τ that falls)
In NEET
10 years of papers
Asked 5 times in 10 years of NEET.
See the past questions: Ohm's Law and Resistance, Current Electricity (chapter)
In JEE Main
42 shifts analysed
65 questions from Current Electricity across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT § "Resistivity of Various Materials" and § "Temperature Dependence of Resistivity"
- By resistivity, materials fall into conductors (metals, low ρ), semiconductors (intermediate ρ) and insulators (very high ρ).
- For metals over a limited range, ρ_T = ρ₀[1 + α(T − T₀)], where α is the temperature coefficient of resistivity; α is positive for metals.
- Metals become more resistive when heated mainly because the relaxation time τ falls (more frequent collisions); n hardly changes.
- Alloys such as nichrome, manganin and constantan have high resistivity and very small temperature coefficient, so they are used in heating elements and standard resistors.
- For semiconductors resistivity decreases with rising temperature (negative α), because the number density of charge carriers n increases with temperature.
- For insulators and semiconductors, the rise in n with temperature outweighs the fall in τ, which is why their behaviour is opposite to metals.
- In problems, ignore the change in the wire's dimensions on heating unless told otherwise; then R changes in the same ratio as ρ.
Questions
5 answers
- What does the "Resistivity as temperature changes" simulation show?
- Resistivity against temperature for copper, manganin and silicon, with meters for carrier density n and relaxation time τ explaining each slope.
- What mistake does the "Resistivity as temperature changes" simulation fix?
- A common mistake it clears up: explaining the rise of a metal's resistance by a change in n (it is τ that falls)
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 5 times in 10 years of papers.
- Does JEE Main ask questions from Current Electricity?
- Yes. JEE Main asked 65 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Resistivity of materials and its temperature dependence" in Current Electricity (Class 12 Physics).
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