Ohmic and Non-Ohmic V-I Characteristics
An ohmic element obeys V = IR with constant R under fixed conditions. Graph slope depends on axes: slope of V versus I is R, while slope of I versus V is conductance.
Why this shows up in the exam
Reading V-I graphs · Comparing wire temperatures · Recognizing nonlinear materials
Learn the idea
A straight V-I relation requires constant resistance; nonlinear carrier response produces a curved characteristic. An ohmic wire at fixed temperature behaves like a constant-slope resistor. If mobility, temperature, or carrier response changes with field, current need not scale linearly with voltage.
🧠 Memory hook: Read the axes before naming the slope.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- R = Delta V/Delta I — slope of a linear V-versus-I graph
- G = Delta I/Delta V = 1/R — slope of a linear I-versus-V graph
- I proportional to Eᵃ — example nonlinear response; infer the graph from the stated exponent
How to approach it
- 1Read axis labels and units
- 2Write the proportionality first
- 3Test whether the slope is constant
Common slip-ups that cost marks
- •Calling every V/I value a constant resistance
- •Reversing resistance and conductance slopes
- •Ignoring self-heating or stated nonlinear drift
🌟 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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