Ohm's law | V-I CHARECTERSTICS | I-V CHARECTERSTICS
Table of contents
What is Ohm's law?
Ohm's law is the fundamental rule connecting voltage (V), current (I) and resistance (R) in electrical circuits. In its simplest form: V = I × R. This means the voltage across a conductor is directly proportional to the current flowing through it when temperature and other physical conditions are constant.
V–I characteristics explained
V–I characteristic is a curve (or line) that shows how voltage varies with current for a particular device. For an ideal resistor that obeys Ohm's law, the V–I curve is a straight line through the origin. The slope of that line corresponds to the resistance. Devices that aren't linear (like diodes or incandescent bulbs) produce curved V–I plots.
I–V characteristics (alternate view)
When you swap the axes you read the same physical information differently: I plotted vs V gives you insight into how much current a device draws for a given applied voltage. For linear devices I–V is still a straight line; for nonlinear devices it highlights thresholds and saturation regions useful in electronics design and troubleshooting.
Practical short tricks & familiar examples
Trick 1 — The 10× check: If you increase voltage by 10× across a fixed resistor, current increases roughly 10×. This quick mental test helps you check if a circuit is roughly linear before more careful measurement.
Example — Light bulb: A cold filament's resistance is lower, so at switch-on the bulb draws a surge current. As the filament heats, its resistance rises and current falls until it reaches steady light output — that's a nonlinear V–I behaviour you see every day.
Measure safely: Always place your meter in series for current measurements and in parallel for voltage. Never place an ammeter directly across a voltage source — it is essentially a low-resistance path and can short the source.
Understanding V–I and I–V charts is essential for designing circuits, choosing resistors, and reading datasheets. Use the straight-line behaviour of resistors to simplify calculations; for complex or temperature-dependent parts, rely on datasheet curves and practical testing.
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