What is the primary difference between the $I-V$ graphs of an Ohmic conductor and a filament lamp?

An Ohmic conductor produces a straight line through the origin, indicating constant resistance. A filament lamp produces an S-shaped curve because its resistance increases as the current heats the filament.

How does the $I-V$ characteristic of a thermistor differ from that of a filament lamp as current increases?

As current increases, a filament lamp's resistance increases (graph gets flatter), whereas a thermistor's resistance decreases (graph gets steeper) due to the release of more charge carriers at higher temperatures.

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

In forward bias, the diode conducts easily once the threshold voltage is reached. In reverse bias, the diode has extremely high resistance and allows virtually no current to flow.

Why is it incorrect to say the resistance of a filament lamp is the reciprocal of the gradient at a point on its $I-V$ curve?

Resistance is defined as the ratio $V/I$ at a specific point. For non-linear graphs, the tangent gradient ($dI/dV$) does not equal the ratio of the total voltage to total current ($I/V$).

What error is made if a student identifies a component as Ohmic just because the graph is a straight line?

The student must also verify that the straight line passes through the origin $(0,0)$. A straight line that misses the origin indicates a non-proportional relationship or a measurement error.

What happens to the interpretation of the gradient if the axes are swapped to a $V-I$ graph?

On a $V-I$ graph (Potential Difference on the y-axis), the gradient represents the resistance $R$ directly, rather than the reciprocal $1/R$.

Define 'Threshold Voltage' in the context of a semiconductor diode.

Threshold voltage is the minimum forward potential difference (usually around 0.6V to 0.7V) required for a diode to begin conducting significant current.

What is an 'Ohmic Conductor'?

An Ohmic conductor is a component that follows Ohm's Law, meaning its resistance remains constant regardless of the potential difference applied, provided physical conditions like temperature are unchanged.

State the mathematical relationship between current, potential difference, and resistance.

The relationship is $V = IR$, where $V$ is potential difference in Volts, $I$ is current in Amperes, and $R$ is resistance in Ohms.

Why does the resistance of a metal filament increase as it gets hotter?

Increased temperature causes the metal ions in the lattice to vibrate more vigorously. these vibrations increase the frequency of collisions with flowing electrons, thus resisting the current flow.

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Current-Potential Difference Graphs

Summary

Current-Potential Difference ( $I-V$ ) graphs illustrate the relationship between the current flowing through a component and the potential difference across it. These characteristic curves allow for the identification of electrical components and the determination of their resistance under varying conditions.

1. Definition & Core Concepts

An $I-V$ characteristic graph plots current ( $I$ ) on the vertical axis against potential difference ( $V$ ) on the horizontal axis.
Components are broadly categorized as Ohmic or Non-Ohmic based on whether they follow Ohm's Law, which states that current is directly proportional to potential difference at a constant temperature.
The shape of the graph reveals how the resistance of the component changes as the electrical conditions vary.

I-V characteristic graphs for a resistor, filament lamp, and diode.

2. Underlying Principles

3. Methods & Techniques

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions