How waves behave while moving around obstacles.
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Teachable Topics:
- Diffraction
- Interference
- Wavelength and Frequency
Theory:
Diffraction is the apparent bending of waves as they move around objects. In this demo we see waves diffract around slits in a barrier. The pattern that results from the diffraction depends on a number of factors, like the size of the slit and the wavelength of the waves. If the width of the slit and the wavelength are close is size to each other, the effects of diffraction become much more noticeable. This can be explained by Huygens' principle.
Huygens' principle states that each point on a wavefront can be considered a source, and these secondary sources create circular waves. These circular waves constructively and destructively interfere with each other in a way that results in the next wavefront. While moving through the slit, the secondary sources on the edge of the slit do not encounter any interference from one side (the side closest to the slit), and as such the wave bends in that direction. This is what causes the waves to spread out after they move through the slit.
Apparatus:
- Ripple Tank
Procedure:
- Set up the ripple tank and turn it on.
- Place two boundaries so that they form a line with a small slit in the middle. Observe the waves after they have moved through the slit.
- Rearrange the boundaries so that they form a line with two slits in the middle. Observe the waves and the interference pattern that forms after they have moved through the slits.