Required Practical: Investigating I 6 Characteristics

Purpose of the Practical

This practical investigates the current-voltage (I 6) characteristics of different electrical components. By measuring how current changes as the potential difference (voltage) across a component varies, you can understand the behaviour of that component in a circuit.

It helps to:

• Identify whether a component follows Ohm 2 Law (linear I 6 relationship) or not.
• Compare the electrical behaviour of components such as resistors and diodes.
• Understand how components respond to forward and reverse bias, especially diodes.

Apparatus and Setup

The key equipment needed includes:

• Variable power supply 6 to adjust the potential difference across the component.
• Ammeter 6 connected in series to measure the current flowing through the component.
• Voltmeter 6 connected in parallel across the component to measure the potential difference.
• Component under test 6 such as a resistor or diode.
• Connecting wires and a breadboard or circuit board 6 to build the circuit.

The circuit is arranged so the power supply, ammeter, and component are in series, with the voltmeter connected across the component.

Procedure

Follow these steps to investigate the I 6 characteristics:

1. Set the power supply to zero volts before switching on.
2. Gradually increase the potential difference in small steps (e.g., 0.2 V increments).
3. At each voltage, record the current shown on the ammeter.
4. Continue increasing the voltage until the maximum safe voltage for the component is reached.
5. Reduce the voltage back down in the same steps, recording current again to check for consistency.
6. Repeat the entire process for different components to compare their I 6 characteristics.

For diodes, it is important to test both forward bias (positive voltage) and reverse bias (negative voltage) to observe their directional behaviour.

Data Presentation and Analysis

Plot the recorded current (I) on the vertical axis against the potential difference (V) on the horizontal axis to create an I 6 graph.

Analyse the graph to identify the component 2 behaviour:

• Linear I 6 graph: Indicates the component obeys Ohm 2 Law; current is directly proportional to voltage. The gradient of the line is the conductance, and the inverse of the gradient gives the resistance.
• Non-linear I 6 graph: Shows the component does not obey Ohm 2 Law (e.g., diode, filament bulb).
• Diode behaviour: Current flows easily in forward bias after a threshold voltage but is almost zero in reverse bias.

Resistance can be calculated from the gradient of the linear part of the graph using:

$$R = \frac{V}{I}$$

For example, if the graph shows a straight line through the origin for a resistor, the resistance is constant. For a diode, the graph shows a sharp increase in current after a certain voltage in forward bias and nearly zero current in reverse bias.

Example: If a resistor has a potential difference of 4 V and the current is 0.2 A, the resistance is:

$$R = \frac{4}{0.2} = 20\,\Omega$$

Safety and Accuracy

To ensure safety and reliable results:

• Use a voltage range that does not overheat or damage the component.
• Check all connections are secure to prevent short circuits or inaccurate readings.
• Avoid leaving the component at high voltage for too long to prevent overheating.
• Repeat measurements to improve reliability and identify any anomalies.
• Switch off the power supply before changing the circuit setup.