# Huygens' Principle, Refraction and Reflection of Plane Waves using Huygens Principle

• The locus of all the particles of the medium which are in the same phase or in the same state of vibration are called wave front
• A point source of Light at finite distance can produce spherical wave front.
• A Line of source of light at finite distance can produce spherical wave front.
• Any source at long distance produces plane wave front.
• According to Huygens every point on the primary wave front acts as a source of secondary wave lets.
• The common tangent (or) envelop of all the secondary wave lets gives the position of new wave front.
• Coherent sources have same wave length and zero (or) constant phase difference
• Mono chromatic sources have same wave length.
• The amplitude of light coming from coherent sources may (or) may not be equal.

### Refraction and Reflection of Plane Waves using Huygens Principle View the Topic in this video From 00:05 To 5:10

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1. Huygen's Principle: According to Huygen's wave theory, each point source sends out waves in all directions propagated by the motion of the particles of the hypothetical medium.
According to the wave theory of light, u that in the medium, then
\tt \mu = \frac{Velocity \ of \ light \ in \ vacuum \ or \ air}{Velocity \ of \ light \ in \ the \ medium} = \frac{c}{\nu}

2. Refraction & reflection of plane wave using huygen's principle
\frac{\nu_{1}}{\lambda_{1}} = \frac{\nu_{2}}{\lambda_{2}}