What does a straight-line IV graph passing through the origin indicate about a component?

It indicates that the component is an Ohmic conductor with constant resistance. This means the current is directly proportional to the potential difference across the component.

How does the IV graph of a filament lamp differ from that of a fixed resistor?

A fixed resistor produces a straight line, whereas a filament lamp produces a curve that flattens at higher voltages. This curvature represents an increase in resistance as the filament heats up.

What is the difference between forward bias and reverse bias in a diode's IV characteristic?

Forward bias allows current to flow easily once a threshold voltage is reached, shown as a sharp rise on the graph. Reverse bias features extremely high resistance, resulting in zero current flow on the negative side of the graph.

What is a common mistake when calculating resistance from a non-linear IV graph?

Students often try to use the gradient of the curve at a point to find resistance. Instead, resistance at any specific point must be calculated using the absolute values of $V$ and $I$ at that point ($R = V/I$).

Why is it incorrect to say current decreases in a filament lamp as voltage increases?

Because current actually increases as voltage increases; however, it increases at a slower rate than it would in a resistor. The resistance is what increases, which limits the rate of current growth.

What error occurs if the voltmeter is placed in series with the component during an IV experiment?

The voltmeter has very high resistance, so placing it in series would effectively block almost all current from flowing through the circuit. This would result in inaccurate readings and a failure to characterize the component.

Define an 'Ohmic Conductor' in the context of IV graphs.

An Ohmic conductor is a component that maintains a constant resistance regardless of the voltage applied, resulting in a linear IV graph that passes through the origin.

What is the mathematical relationship between the gradient of an IV graph and resistance?

On a standard IV graph (Current on y-axis, Voltage on x-axis), the gradient is equal to the reciprocal of the resistance ($1/R$). Therefore, a steeper gradient represents a lower resistance.

What is the threshold voltage in a diode IV graph?

It is the minimum forward voltage required for the diode to start conducting significant current. On the graph, this is the point where the current line suddenly curves upward from the zero-axis.

Why does the resistance of a filament lamp increase at higher voltages?

Higher voltage drives more current, which increases the temperature of the filament. The increased thermal energy causes metal ions to vibrate more, creating more frequent collisions with electrons and hindering their flow.

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2. Electricity

IV Graphs

Summary

IV graphs are graphical representations used in physics to illustrate the relationship between the current ( $I$ ) flowing through an electrical component and the potential difference ( $V$ ) across it. By analyzing the shape and slope of these curves, one can determine whether a component's resistance is constant or variable, providing critical insights into the component's physical properties and behavior under different electrical loads.

1. Definition & Core Concepts

An IV Graph plots current ( $I$ ) on the vertical y-axis and potential difference ( $V$ ) on the horizontal x-axis to characterize electrical components.

The relationship between these two variables defines the resistance ( $R$ ) of the component, derived from the fundamental formula $V = IR$ , or $R = \frac{V}{I}$ .

Components are broadly categorized as Ohmic (linear relationship) or Non-Ohmic (non-linear relationship) based on the resulting shape of their IV curve.

In a standard IV plot, a steeper slope indicates lower resistance, while a shallower (flatter) slope indicates higher resistance, assuming current is on the y-axis.

IV Graph showing characteristic curves for a fixed resistor (straight line), filament lamp (S-curve), and diode (zero current then sharp rise).

2. Underlying Principles

3. Methods & Techniques

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions

IV Graphs

Summary

1. Definition & Core Concepts

An IV Graph plots current ( $I$ ) on the vertical y-axis and potential difference ( $V$ ) on the horizontal x-axis to characterize electrical components.

The relationship between these two variables defines the resistance ( $R$ ) of the component, derived from the fundamental formula $V = IR$ , or $R = \frac{V}{I}$ .

Components are broadly categorized as Ohmic (linear relationship) or Non-Ohmic (non-linear relationship) based on the resulting shape of their IV curve.

In a standard IV plot, a steeper slope indicates lower resistance, while a shallower (flatter) slope indicates higher resistance, assuming current is on the y-axis.

IV Graph showing characteristic curves for a fixed resistor (straight line), filament lamp (S-curve), and diode (zero current then sharp rise).

2. Underlying Principles

Ohm's Law states that for certain components at a constant temperature, the current is directly proportional to the potential difference ( $I \propto V$ ).

For Ohmic conductors, such as fixed resistors or wires at a stable temperature, the IV graph is a straight line passing through the origin $(0,0)$ .

Non-Ohmic behavior occurs when the resistance changes as the current or voltage changes, often due to environmental factors like temperature or light.

In a filament lamp, as current increases, the metal filament heats up, causing atoms to vibrate more vigorously and increasing the frequency of collisions with flowing electrons, which raises resistance.

3. Methods & Techniques

To generate an IV graph, a circuit must be constructed containing the component under test, a power source, an ammeter, and a voltmeter.

The ammeter must be connected in series with the component to measure the current flowing through it, while the voltmeter must be connected in parallel to measure the potential difference across it.

A variable resistor or a variable power supply is used to systematically change the current and voltage levels in the circuit.

Data points are collected by recording the voltmeter and ammeter readings at various intervals, including reversing the power supply connections to obtain negative values for the graph.

4. Key Distinctions

It is vital to distinguish between components that allow bidirectional flow and those that are unidirectional.

Component	Graph Shape	Resistance Behavior
Fixed Resistor	Straight line through origin	Constant resistance
Filament Lamp	Curved 'S' shape	Resistance increases with temperature/voltage
Diode	Horizontal line then sharp rise	Infinite resistance in reverse; low in forward
Thermistor	Non-linear curve	Resistance decreases as temperature increases

A diode acts as a one-way valve; it has extremely high resistance in 'reverse bias' (negative voltage) and very low resistance in 'forward bias' once a threshold voltage is reached.

5. Exam Strategy & Tips

Always check the axes: while most IV graphs put $I$ on the y-axis, some exams may swap them ( $VI$ graph). If $V$ is on the y-axis, the slope represents the resistance $R$ directly.

When describing a filament lamp graph, use the term 'decreasing rate of increase' for current; as voltage increases, current still goes up, but more slowly due to rising resistance.

For diode questions, remember that the graph should show zero current for all negative voltages and small positive voltages until the 'threshold' is met.

Verify proportionality: if a graph is a straight line but does not pass through the origin, the variables are linear but not directly proportional.

6. Common Pitfalls & Misconceptions

A common error is assuming that a curved IV graph means the component does not follow the equation $V=IR$ . The equation still applies at any specific point, but the value of $R$ is simply not a constant.

Students often confuse the IV characteristics of an LDR (Light Dependent Resistor) with a thermistor; while both are non-linear, their resistance changes based on different external stimuli (light vs. heat).

In a filament lamp, do not say 'current decreases' as voltage increases. The current still increases, but the gradient of the graph decreases because resistance is rising.