Principle
In this experiment the students should come to realize that in
the shadow area behind a narrow obstacle regular patterns of
brightness will be found which are formed by diffraction at the
edges of the obstacle. By comparing the diffraction pattern with
that created by diffraction at a slit having the same width as the
obstacle, they should gain an understanding of
Babinet's Principle and find it confirmed.
Babinet's Principle states that diffraction phenomena behind
complementary screens are identical. This diaphragm employed has a
slit and a plate (narrow obstacle) of identical size; they act as
screens which are complementary to each other, i.e. together they
bring about total extinction. Therefore, in the observation plane
the amplitudes of the waves which interfere following diffraction
at a slit or obstacle, must be identical but phase displaced by
180°.
Benefits
- Multifunctional light box - All-in-one: Can be used for geometric optics on the table, colour mixing and on an optical bench
- Extension with others sets at anytime, no additional light sources needed, recognition value for students
Tasks
What sort of shadow is created behind a narrow obstacle? Direct
a narrow pencil of light onto a slender obstacle so that part of
the beam grazes the side. Observe the shadow thus created and
compare it with the diffraction pattern formed when the light
beam strikes a slit of the same width as the obstacle.
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