Verify Inverse Square Law for a Point Source of Light

Introduction

• In physics, we often encounter the concept of the inverse square law, which describes how a physical quantity changes concerning the distance from a point source. In this experiment, we will verify the inverse square law for a point source of light.

Experimental Setup

• Apparatus: To conduct this experiment, you will need the following equipment:

  • A clear lamp with a small filament as the point source of light.
  • A darkened room.
  • A light sensor.
  • A ruler.
  • A black surface.

• Ambient Light Measurement: Before starting the experiment, measure the ambient light level in the darkened room with the lamp turned off. This measurement will serve as a reference, and you will subtract it from all light measurements during the experiment.

• Distance Variation: Using the ruler as a reference, vary the distance (r) of the light sensor from the centre of the lamp. Ensure that you maintain a constant area for the light sensor.

• Irradiance Measurement: Record the light sensor reading as the irradiance (E). This measurement represents the light intensity due to the lamp.

• Data Collection: Repeat the distance and irradiance measurements for various distances from the lamp.

Data Analysis

• Plot the irradiance (E) against one over the distance squared (1/r²).
• The resulting graph will illustrate the relationship between irradiance from a point source and the distance from the source.

Observations

• You will notice that the graph shows a straight line with a positive gradient.

---

Verify Inverse Square Law for a Point Source of Light

Conclusion

• The straight-line graph demonstrates that irradiance increases as the distance (r) from the point source increases.
• This observation verifies the inverse square law for a point source of light.

Summary

• The experiment involves measuring irradiance from a point source of light at various distances.
• The data is used to create a graph, confirming that irradiance is inversely proportional to the square of the distance from the source, consistent with the inverse square law.