Single Slit Experiment

This experiment proves that light undergoes DIFFRACTION, and hence LIGHT is a WAVE.
A thin rectangular piece of glass is painted with black paint, and a thin single slit is made on the paint with a razor blade. This allows light to pass through in a thin beam.

Important Points

White Light
A beam of white light is shone through the slit.

Observation
1) A broad central band of bright white light is observed.
2) This is flanked by alternate spectral color fringes and black fringes.


If RED light is used:

1) Fringes are more distinct
2) Broad central band of RED is observed
3) Alternate bands of Red and Black are observed.

Red Light is MONOCHROMATIC.
(light of single frequency)


If BLUE light is used:

1) Fringes are very distinct.
2) Broad central band of BLUE is observed
3) Alternate bands of Blue and Black are observed.
4) The bands are CLOSER than in the case of the RED.
5) The DIFFRACTION is lesser.
This shows that BLUE light has a SMALLER WAVELENGTH than RED light.

Blue Light is MONOCHROMATIC
(light of single frequency)


IMPORTANT POINTS

1. What is the effect of the WIDTH of the slit on the amount of DIFFRACTION?
A narrower width produces greater diffraction.

2. What does DIFFRACTION prove about light?
DIFFRACTION proves that LIGHT is a WAVE.

3. For what TYPE of wave does diffraction occur?
Diffraction occurs for BOTH TRANSVERSE and LONGITUDINAL WAVES.

4. What does DIFFRACTION of light NOT INDICATE about light?
Diffraction DOES NOT indicate whether LIGHT is transverse or longitudinal since diffraction occurs for both types of waves.

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