The item displays the interference pattern produced by wave crests propagating outward from two point sources (circular wavefronts). The separation between the sources can be changed as can the wavelength. The pattern is observed as the wavefronts propagate. The pattern can be paused. The path difference can be measured to any point on the screen using simple point and clicks.
Type of Material:
Lecture/Demonstration
Technical Requirements:
Works well on both IE5.5 and Netscape 4.75. The start button image on the initial page did not load at times (but the hotspot still works). The simulations opens up to a small screen but can be enlarged for better viewing.
Identify Major Learning Goals:
Understanding concepts relating to wave interference, in particular relating to a double slit interference pattern. Investigate relations between slit separation, wavelength, and path difference.
Target Student Population:
Lower level undergraduate, Introductory Physics (High school and college)
Prerequisite Knowledge or Skills:
Basic understanding of Superposition and Interference, Huygens Principle, and wave propagation.
Content Quality
Rating:
Strengths:
The graphics are used effectively. The user can open multiple screens to give qualitative comparisons. The user can vary wavelength, slit spacing and measure path difference.
This is a simple and effective demonstration of the interference of waves emanating from two narrow slits. Easy to operate and straightforward.
You are able to observe lines (not drawn lines) that indicate constructive or destructive fringes.
Concerns:
Some additional description of the item may be useful, including a comment that the circles and straight lines represent traveling wavecrests.
Potential Effectiveness as a Teaching Tool
Rating:
Strengths:
Recommended Use(s) for Material: Lecture/Demo
Regions of maximum constructive interference are visually apparent. Path difference at different locations on the pattern can be examined quantitatively.
Concerns:
Use(s) Material is not Suited For: Tutorial, Self-Study, Detailed analysis of interference patterns.
Units are not used for slit distance or wavelength. There should be discussion about the importance of the ratio of these quantities.
The path difference is negative when examining a point in the upper half of the screen. This is contrary to typical sign conventions (lower path minus upper) that are used to make path difference positive when angle is usually considered positive.
The lack of accurate description and lack of quantitative analysis of intensity may limit the uses for student self-study.
General Comments on Effectiveness: The applet is visually effective, with regions of maximum interference clearly visible. However these constructive interference regions appear white (for high average intensity regions), but the peaks or wavecrests are displayed as black. The effect is very visible for small wavelength.
One can easily determine conditions such that the path difference is an integral number of wavelengths using the red triangular markers. An improvement would be to allow for switching to a view that displays a gray scale representing intensity at each point (or time average intensity).
Ease of Use for Both Students and Faculty
Rating:
Strengths:
The simulation runs well and offers a quick and easy demonstration of wave interference.
Concerns:
The uses are currently limited to investigations involving path difference (not intensity) and require guidance.
Some features are not documented. For example, the user can change the slit separation but this is not reflected in the distance box. Also, clicking the right mouse button toggles the effect of the left mouse button.
General Comments on Usability: The applet is able to easily illustrate some of the qualitative features of the double slit interference pattern. Quantitative investigation can be performed regarding path difference at a particular screen position or fringe. The item does not include measurement tools that might indicate the relation between fringe order number and path difference (label fringes on the screen or right hand wall). Inclusion of information allowing intensity to be quantitatively examined and visually represented would be of use. Current use as is may require teacher guidance and development of worksheet style materials.
Creative Commons:
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