Key relationship
R=ρ₂₀L[1+α(T−20)]/A; σ=1/ρ.
Physics · Class 12
Resistivity and temperature
Length and cross-section control resistance independently of the material resistivity. The linear temperature relation is valid over a limited range.
Open the interactive experiment →Resistivity and temperature
கம்பி நீளம் அதிகரித்தால் மின்தடை அதிகரிக்கும்; குறுக்குப் பரப்பு அதிகரித்தால் குறையும். உலோக மின்தடை வெப்பத்துடன் உயர்கிறது.
Key notes, relationships and model limits
Remember
Length and cross-section control resistance independently of the material resistivity. The linear temperature relation is valid over a limited range.
Common trap
Resistance also depends on length and cross-sectional area. Resistivity is the material property at a stated temperature.
Model limits
Uniform cylindrical conductor with linear positive temperature coefficient; no self-heating feedback.
What you will learn
Use the controls and plotted relation to explain resistivity and temperature.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
A 1 m copper wire with 1 mm² area and ρ=1.68×10⁻⁸ Ω m has R=0.0168 Ω at 20 °C.
Why this matters
The model connects resistivity and temperature with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
Doubling cross-sectional area changes resistance to?
- Twice its previous value.
- Half its previous value.
- One quarter of its previous value.
Read the explanation
Half its previous value.
Course connection: Class XII Chapter 3. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.