What is the primary difference between a linear and a non-linear I-V characteristic?

A linear characteristic is a straight line through the origin where current is directly proportional to voltage (constant resistance). A non-linear characteristic is curved, indicating that the resistance changes as the voltage or current changes.

How does the I-V graph of a filament lamp differ from that of a fixed resistor?

A fixed resistor produces a straight-line graph because its resistance is constant. A filament lamp produces an S-shaped curve because its resistance increases as the filament gets hotter at higher voltages.

Compare the behavior of a diode in forward bias versus reverse bias.

In forward bias, the diode allows current to flow easily once a threshold voltage is met. In reverse bias, the diode has extremely high resistance, effectively blocking current flow and resulting in a flat line at zero on the I-V graph.

What is a common error when connecting a voltmeter to measure I-V characteristics?

Connecting the voltmeter in series instead of parallel is a frequent mistake. Because voltmeters have very high resistance, placing them in series will block almost all current from flowing through the circuit.

Why might a student's I-V graph for a 'fixed' resistor start to curve at high voltages?

This happens due to the heating effect of the current. If the voltage is too high, the resistor warms up, increasing the vibration of its ions and causing the resistance to rise, which turns the linear relationship into a non-linear one.

What error occurs if the ammeter is placed in parallel with the component being tested?

Ammeters have very low resistance; placing one in parallel creates a short circuit. Most of the current will bypass the component and flow through the ammeter, potentially damaging the meter and giving incorrect readings for the component.

Define an 'Ohmic Conductor' in the context of I-V graphs.

An Ohmic conductor is a component that obeys Ohm's Law ($V=IR$), resulting in a linear I-V graph that passes through the origin at a constant temperature.

What does the gradient of an I-V graph represent?

The gradient represents the reciprocal of the resistance ($1/R$). A steeper gradient indicates a lower resistance, while a shallower gradient indicates a higher resistance.

What is a Light-Emitting Diode (LED)?

An LED is a specific type of diode that emits light when current flows through it in the forward direction. It shares the same non-linear I-V characteristic as a standard diode.

Why does the resistance of a filament lamp increase as the voltage increases?

Higher voltage increases the current, which heats the filament. The increased temperature causes metal ions in the filament to vibrate more, making it harder for electrons to pass through, thus increasing resistance.

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1. Electricity, Energy & Waves

I-V Characteristics

Summary

I-V characteristics describe the functional relationship between the current ( $I$ ) flowing through an electrical component and the voltage ( $V$ ) applied across it. By analyzing the shape of an I-V graph, one can determine whether a component is linear (Ohmic) or non-linear, providing critical insights into how resistance changes under different operating conditions.

1. Definition and Core Concepts

I-V Characteristics refer to the graphical representation of how current varies as a function of potential difference (voltage) for a specific circuit element.
Components are classified as linear if their I-V graph is a straight line passing through the origin, indicating that current is directly proportional to voltage.
Non-linear components exhibit curved I-V graphs, meaning their resistance is not constant and changes depending on the magnitude or direction of the applied voltage.

I-V Characteristic graphs for a fixed resistor (linear), a filament lamp (curved), and a diode (one-way conduction).

2. Underlying Principles: Ohm's Law and Resistance

For linear components, the relationship is governed by Ohm's Law, which states that $V = IR$ , where $R$ is the resistance measured in Ohms ( $\Omega$ ).
In a linear I-V graph, the gradient (slope) is equal to $1/R$ ; therefore, a steeper line represents a lower resistance, while a shallower line represents a higher resistance.
Resistance arises from collisions between flowing electrons and the positive ions within the material's lattice structure, which converts electrical energy into thermal energy.

3. Behavior of Non-Linear Components

4. Experimental Methodology

5. Key Distinctions

6. Exam Strategy & Tips