### What is diffraction?

• ability of waves to travel around corners and obstacles in their path
• ability of waves to spread out in wavefronts as they pass through a small aperture or a sharp edge
• diffraction occurs for both transverse and longitudinal waves
• amount of diffraction increases with increasing wavelength
• if a light beam is observed to have a high diffraction, it must have a high wavelength (low frequency)
• therefore amount diffraction can be used to analyse wavelengths
Waves of HIGHER WAVELENGTH produce GREATER DIFFRACTION.

Since the RED light shows a higher diffraction, the RED light has a LARGER WAVELENGTH.
Further, this means that RED has a LOWER FREQUENCY than blue.

Huygens Principle
Explanation for Diffraction
Each point on a wave front can be considered to be a centre of disturbance for a new source of waves.

#### Important Notes

1. Narrower slits produce larger diffraction.

2. If RED light is used: (red and black bands observed)

• fringes are more distinct
• broad central band of red light, with red and black bands
• red has a large wavelength and is diffracted a lot
• bands are wider
• red light is monochromatic : it is of single frequency

3.If BLUE light is used: (blue and black bands observed)

• fringes are more distinct
• broad central band of blue light, with blue and black bands
• blue has a smaller wavelength and is diffracted lesser
• therefore bands are narrower
• blue light is monochromatic : it is of single frequency