Education and Manpower Bureau
Using Datalogger in the Teaching of Physics

Diffraction and Interference of Light Waves

Experiment Profile:

1. Background

This experiment gives very clear graphical proof to students about the diffraction and interference nature of light waves. We can get similar results by replacing the light sensor and light source with sound sensors and 2 sound sources.

2. Objective

 To observe the diffraction patterns of light. To study the interference effects from two slits (Young's slits).

3. Equipment List

 Datalogger interface connected to a PC Light sensor Double slits Light source

 Experiment Diffraction and Interference of Light Waves Sound Beats

 Procedure.

 1 Connect the datalogger interface to a PC with the software installed. 2 Connect the light sensor to the appropriate channel of the interface. See Figure 1. 3 Set up a light source at one end of the table. 4 Place a card with double slits in front of the light source. The distance between the slits is very small compared to the distance between the slits with the light sensor. 5 Place the light sensor at the other end of the table. 6 Start the data-logging software to collect data. 7 Move the light sensor at a horizontal level and keep a constant distance between the sensor and the slits when recording the data. 8 Stop the data collection. 9 Observe a single-slit and a double-slit pattern.

Analysis:

 1 Plot a graph of light intensity against distance. What can you observe in the graph? 2 Does light have interference and diffraction characteristics of waves? If yes, please explain. 3 From the observed pattern, determine the wavelength of the light source. 4 Change the distance between the slits and observe the change in pattern. 5 Change the wavelength and observe the pattern.

Extensive:

 1 How can you check if light shows wave properties? If light is a wave, it should bend around corners; it is not immediately apparent that light does bend around corners in the same way sound or water waves do. This model helps demonstrate that light does have these properties. 2 Can light waves interact to produce regions of darkness? Waveforms show destructive as well as constructive interference. This model demonstrates that light from more than one source can interact to produce regions of darkness.

Video Download:

 Acknowledgements We are particularly grateful to SKH Kei Hau Secondary School for their help in the production of this video.

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2003