current electricity vi characteristics

Learn V-I graphs of resistors, diodes, Zener diode, LED, photodiode, capacitor and inductor with formulas, slope concepts and exam questions.

Current Electricity | Graphs | Devices

Current Electricity - V-I Characteristics

current electricity v-i characteristics are explained with resistor graphs, diode graphs, Zener diode, LED, photodiode, capacitor response, inductor response, formulas and exam questions for CBSE, NEET, JEE Main, JEE Advanced, Olympiad, AP Physics, IB, IGCSE and A-Level Physics.

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1. Formula Sheet First

V = IROhmic resistor

I = V/RCurrent

R = V/IResistance

Slope of V-I = RVoltage on y-axis

Slope of I-V = 1/RCurrent on y-axis

P = VIPower

P = I²RHeating form

P = V²/RVoltage form

I = I₀(e^eV/kT - 1)Diode equation

V_z = constantZener breakdown

I = C dV/dtCapacitor

V = L dI/dtInductor

Symbols: V = voltage, I = current, R = resistance, P = power, I₀ = reverse saturation current, e = electronic charge, k = Boltzmann constant, T = absolute temperature, C = capacitance, L = inductance.

2. What Is V-I Characteristic?

A V-I characteristic is a graph showing how voltage and current are related for a device. It tells whether the device is ohmic or non-ohmic, linear or non-linear, and whether resistance is constant or changing.

V-I graph: voltage is plotted against current. Slope gives resistance R.

I-V graph: current is plotted against voltage. Slope gives conductance 1/R.

3-11. V-I Characteristics of Important Devices

Ohmic Resistor

Straight line through origin, constant resistance, obeys Ohm's law.

Non-Ohmic Resistor

Curved graph because resistance changes with current, voltage or temperature.

Filament Bulb

Initially low resistance; heating increases resistance, so graph bends.

Diode

Forward current rises after knee voltage. Reverse current is tiny until breakdown.

Zener Diode

Reverse breakdown gives nearly constant voltage Vz, useful in regulation.

LED

Forward biased diode emits light; resistor is needed to limit current.

Photodiode

Reverse bias current increases with light intensity; used in light detection.

Capacitor and Inductor

Capacitor: I = C dV/dt, open circuit in DC steady state. Inductor: V = L dI/dt, opposes current change.

12. Comparison Table

Device	Nature	Formula	Exam Point	Application
Resistor	Linear, ohmic	V = IR	Straight line through origin	Current control
Filament bulb	Non-linear	R rises with T	Heating changes resistance	Lighting
Diode	Non-linear	I = I₀(e^(eV/kT)-1)	Knee voltage	Rectifier
Zener	Breakdown region	Vz constant	Voltage regulator	Regulation
LED	Forward diode	Threshold voltage	Needs resistor	Indicator/light
Photodiode	Light dependent	Photocurrent	Reverse bias operation	Sensor
Capacitor	Transient	I = C dV/dt	Open in DC steady state	Filters/timing
Inductor	Transient	V = L dI/dt	Opposes current change	Chokes/filters

13-18. Exam Question Bank With Accordion Solutions

Click each question to open the answer.

19. Common Student Mistakes

20. Final Revision Sheet

V-I slope: R when V is on y-axis.

I-V slope: conductance = 1/R when I is on y-axis.

Ohmic: straight line through origin at constant temperature.

Diode: current rises sharply after knee voltage.

Zener: constant reverse breakdown voltage.

Capacitor/Inductor: transient devices, not simple DC resistor V-I graphs.

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