Objective
The objective of this experiment is to investigate the characteristics of carbon film resistors in low power circuits. It aims to demonstrate their behavior, stability, and efficiency under low voltage and current conditions.
Materials Needed
- Carbon film resistors (various resistance values)
- Low voltage power supply (e.g., 5V or 12V)
- Multimeter (for measuring voltage and current)
- Breadboard and jumper wires
- LED (for visual indication of current flow)
- Optional: potentiometer (for variable resistance)
Theory
Carbon film resistors are made by depositing a thin layer of carbon on a substrate. They offer good thermal stability and are widely used in low power applications. The power dissipation of a resistor can be calculated using:
P = V^2 / R
Where **P** is the power (in watts), **V** is the voltage across the resistor (in volts), and **R** is the resistance (in ohms). This experiment focuses on ensuring that the power dissipated remains within safe limits for the resistor.
Steps
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Set Up the Circuit
Connect the carbon film resistor in series with the LED and the low voltage power supply on the breadboard. Ensure that the polarity of the LED is correct (anode connected to positive and cathode to negative).
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Initial Measurements
Measure the resistance of the carbon film resistor using a multimeter to confirm its rated value. Record this value for reference.
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Apply Power
Turn on the low voltage power supply. Monitor the LED for illumination, indicating current flow through the circuit. Observe the brightness of the LED as an indicator of current levels.
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Measure Voltage and Current
Using the multimeter, measure the voltage across the resistor and the current flowing through the circuit. Record these values in a data table for analysis.
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Experiment with Different Resistors
Repeat the measurements with different carbon film resistors to observe how varying resistance values affect the current and voltage. This can also be done with a potentiometer to adjust the resistance dynamically.
Data and Calculations
Record the voltage and current at various resistor values. Below is a sample data table:
| Resistance (Ω) | Voltage (V) | Current (A) | Power (W) |
|---|---|---|---|
| 220 | 5 | 0.0227 | 0.1139 |
| 330 | 5 | 0.0152 | 0.0765 |
| 470 | 5 | 0.0106 | 0.0530 |
In this example, the power dissipation is calculated for different resistor values under the same voltage supply.
Conclusion
This experiment highlights the effectiveness of carbon film resistors in low power circuits. Their stability and reliability make them suitable for various electronic applications where low power dissipation is crucial. By understanding their characteristics, designers can make informed choices in selecting resistors for their circuits.