Physics · Class 12

Ohmic and non-linear VI curves

An ohmic element has a constant V/I ratio at fixed temperature. The illustrative filament model increases resistance with heating and bends the VI curve.

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Ohmic and non-linear VI curves

நிலையான வெப்பத்தில் ஓமிக் கடத்தியின் V/I மாறாது. இழை விளக்கின் வெப்பம் மின்தடையை மாற்றும்.

Key notes, relationships and model limits

Key relationship

Iohmic=V/R; Ilamp=V/[R₀(1+β|V|)].

Remember

An ohmic element has a constant V/I ratio at fixed temperature. The illustrative filament model increases resistance with heating and bends the VI curve.

Common trap

Ohm’s law requires an ohmic element under fixed physical conditions; a changing filament temperature produces a curved VI relation.

Model limits

Ohmic constant-temperature resistor with an ideal series switch; an open switch stops current and power. Lamp is a stated phenomenological resistance law, not a measured tungsten calibration.

What you will learn

Use the controls and plotted relation to explain ohmic and non-linear vi curves.

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

For R=10 Ω, 12 V gives 1.2 A. With β=0.1/V the illustrative hot filament gives ≈0.545 A.

Why this matters

The model connects ohmic and non-linear vi curves with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

Which VI curve has constant resistance?

Any smooth curve through the origin.
A straight line through the origin.
A curve with current flattening at high voltage.

Read the explanation

A straight line through the origin.

Course connection: Class XII Chapter 3. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.