Physics in Action

Two-Point Source Interference

Materials: Word Processor

Time Allotment: 3 Class Days


This makeup lab is unique from most others in that it does not actually involve a laboratory exercise. Rather, this makeup lab involves the completion of a writing assignment which demonstrates your understanding of two-point source interference and its applications.

The Assignment:

We have been discussing 2-pt. source interference phenomenon and a variety of applications. These phenomena (and others) were discussed in class and accompanied by labs and demonstrations. Each 2-pt. source interference phenomenon involves the interference of either a sound wave, a light wave, or some other type of wave emmanating from two points. Select one of the phenomena discussed in class or in the textbook and consider how it might be clearly and understandably explained to a peer. Then write a short letter in which you do just that - explain the phenomenon to a peer. In your explanation, be sure to include the following:

  1. identify what is meant by two-point source interference.
  2. describe what causes two-point source interference, including a definition and discussion of constructive interference, destructive interference, nodes, and antinodes.
  3. describe the effect of two-point source interference for the particular type of wave which you have chosen.
  4. explain the mathematics of two-point source interference.
  5. include some form of an instructive, well-labeled diagram which complements your explanation of the mathematics.
  6. provide one relatively simple calculation which fits the phenomenon you are discussing.

To enhance the appearance of your letter, consider one of the following options:



Your writing assignment/makeup lab will be assessed using the following scoring rubric.

1.Physics Understanding

Demonstr'd understanding of two-point source interference by an accurate description and explan'n of a real-world phenomenon; utilized the vocab of physics to produce understandable ( to an eight grader) explan'ns; diagrams are a helpful complement to verbal explan'ns.

0 - 2

Understanding level is unsatisfactory as demonstrated by a description and explanation which is incorrect and faulty; the vocabulary of physics may have been misused or not even used at all

3 - 4

Made an effort to describe and explain a real-world 2-point source interference phenomenon using the vocab of physics; explanations are satisfactory, yet lack in either detail, completeness, accuracy or vocabulary usage; diagram may be lacking detail or irrelevant to writing.

5 - 6

Utilized physics vocab to produce an accurate description of a real-world 2-pt. source interference phenomenon; explanations are insightful and complete; diagram is helpful and instructive; no major errors or omissions; writing is in your own words.

2. Diagramming

Constructed a diagram which is relevant to the discussion and complements the explanations; used labels to clarify its meaning.


Failed to construct a diagram to accompany explanation

0.5 - 1

Diagram has limited usefulness due to lack of detail or irrelevancy to writing.

1.5 - 2

Diagram is instructive, well-labeled, and relevant to discussion

3. Writing Organiz'n

Involves a logical/sequential flow of ideas; utilized sufficient transitions; easy to follow thought process.


A good example of linguistic gymnastics


Only a few mistakes


Very Good

Total = _________/10

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This page created by Tom Henderson and last updated on 8/7/97.