I 6V Graphs

Understanding I 6V Graphs

An I 6V graph shows how the current (I) through a component varies with the potential difference (V) across it. The current is plotted on the y-axis and the potential difference on the x-axis.

Different electrical components have characteristic I 6V graphs that reveal how they behave under changing voltage:

• Ohmic conductors (like a metal wire at constant temperature) show a straight line through the origin.
• Non-ohmic components have curved I 6V graphs, indicating that their resistance changes with voltage or current.

Linear behaviour means the current is directly proportional to the potential difference. Non-linear behaviour means this proportionality does not hold.

For example, a filament lamp 27s I 6V graph is curved because its temperature changes as current flows, affecting its resistance.

Learning example: For a metal wire, if the potential difference is 2 V and the current is 0.5 A, the graph point is (2, 0.5). If the potential difference doubles to 4 V and the current doubles to 1 A, the points lie on a straight line, showing linear behaviour.

For instance, if a component has a potential difference of 3 V and a current of 0.6 A, its resistance can be calculated as $R = \frac{V}{I} = \frac{3}{0.6} = 5 \Omega$.

Ohm 27s Law and Graphs

Ohm 27s Law states that for some conductors (called ohmic conductors), the current through the conductor is directly proportional to the potential difference across it, provided the temperature remains constant.

On an I 6V graph for an ohmic conductor, this relationship produces a straight line through the origin. The gradient (slope) of this line is important:

Gradient = $\frac{\text{Current (I)}}{\text{Potential difference (V)}}$

Actually, the gradient is $\frac{I}{V}$, but since resistance $R = \frac{V}{I}$, the inverse of the gradient gives the resistance.

So, a steeper gradient means a higher current for a given voltage, which means a lower resistance.

Temperature affects the I 6V graph because resistance usually increases with temperature for metals. As the temperature rises, the graph becomes less steep (flattens), showing increased resistance.

For example, a filament lamp 27s resistance increases as it heats up, so its I 6V graph curves and is not a straight line.

Interpreting Graph Features

The slope of an I 6V graph is key to understanding the resistance of the component:

• Constant slope (straight line) means constant resistance.
• Changing slope (curved graph) means resistance changes with current or voltage.

Curves on the graph show how resistance varies. For example, if the curve gets steeper as voltage increases, resistance is increasing.

You can identify components from their I 6V graph shape:

• Ohmic conductor: straight line through origin.
• Filament lamp: curve that flattens at higher voltages (resistance increases with temperature).
• Diode: current flows only in one direction, so the graph shows current for positive voltages but almost zero current for negative voltages.

Required Practical: I 6V Characteristics

To investigate I 6V characteristics, you set up a circuit with the component, a variable power supply, an ammeter in series, and a voltmeter in parallel with the component.

Steps:

1. Start with zero voltage and gradually increase the potential difference in small steps.
2. At each step, record the current from the ammeter and the potential difference from the voltmeter.
3. Plot the current (y-axis) against the potential difference (x-axis) to get the I 6V graph.

Repeat by decreasing the voltage to check for consistency.

Different components produce different I 6V graphs, which you can analyse to understand their behaviour.

Learning example: Suppose you measure the following for a metal wire:

Potential Difference (V)	Current (A)
0.5	0.1
1.0	0.2
1.5	0.3
2.0	0.4

Plotting these points gives a straight line through the origin, confirming ohmic behaviour.