Wave Optics Class 12 Notes

Greetings to all, Today we are going to upload Wave Optics Class 12 Notes PDF to assist all the students as well as tutors. CBSE Chapter Notes for all chapters of Class 12th Physics are public here. Notes based on Class 12 NCERT textbooks and latest CBSE class 12th Physics syllabus 2021- 2022. These important notes are very useful for revision. The weightage of each chapter in CBSE Class 12 Physics board exam 2022 given the latest CBSE Class 12th Physics Syllabus.

Wave Optics Class 12 Notes PDF

Wave Front:
A light source is a point that emits disturbance in all directions. In a homogeneous medium, the disturbance reaches all those particles of the medium in phase, which are located at the same distance from the source of light, and hence at all the time, every particle must be vibrating in phase with each other. The locus of all the particles of the medium, which at any instant are vibrating in the same phase, is called the wave front.
Depending upon the shape of the source of light, wave front can be the following types:

1. Spherical wave front
2. Cylindrical wave front

Spherical Wave Front: 
A point source of light produces a spherical wave front. This is because the locus of every point, which is equidistant from the point source, is a sphere
 Cylindrical Wave Front: 
If the light source is linear (such as a slit), it produces a cylindrical wave front. Here, every point, which is equidistant from the linear source, lies on the surface of a cylinder.
Plane Wave Front: 
A wavefront will appear plane if it is a small part of a spherical or a cylindrical wavefront I originating from a distant source. So it is called a plane wavefront
Ray of Light: 
The path along which light travels is known as a ray of light. If we draw an arrow normal to the wavefront and which points in the direction of propagation of disturbance represents a ray of light. In a ray diagram, thick arrows represent the rays of light.
It is also called the wave normal because the ray of light is normal to the wavefront.
Key Points: 

• If we take any two points on a wavefront, the phase difference between them will be zero.

Huygens’s Principle: 
Huygens’s principle is a geometrical construction, which can be used to obtain the new position of a wavefront at a later time from its given position at any instant. Or we can quote that this principle gives a method that gives an idea about how light spreads out in the medium.
It is developed on the following assumptions:

1. All the points on a given or primary wavefront act as a source of secondary wavelets, which sends out a disturbance in all directions in a similar manner as the primary light source.
2. The new position of the wavefront at any instant (called secondary wavefront) is the envelope of the secondary wavelets at that instant.

These two assumptions are known as Huygens’s principle or Huygens’ construction.
Key Point: 

• Huygens principle is simply a geometrical construction to find the position of a wavefront at a later time.

 Principle of Superposition:
If two or more than two waves superimpose each other at a common particle of the medium then the resultant displacement
(y)(y)
of the particle is equal to the vector sum of the displacements (
y1y1
and
y2 y2
) produced by individual waves  .i.e  y→=y1→+y2→y→=y1→+y2→
Phase/Phase difference/Path difference/Time difference

1. Phase: Phase is defined as the argument of sine or cosine in the expression for displacement of a wave. For displacement  y = asin ωty = asin ωt ; term  ω t = ω t = phase or instantaneous phase.
2. Phase Difference (ϕ)(ϕ): Phase difference is the difference between the phases of two waves at a point. i.e. if y1=a1sin ωty1=a1sin ωt and y2=a2sin( ω t+ϕ)y2=a2sin( ω t+ϕ) so phase difference =ϕ=ϕ

iii. Path Difference  (Δ)(Δ): Path difference between the waves at that point is the difference in path lengths of two waves meeting at a point. Also  Δ = λ 2 π  × ϕ Δ = λ 2 π  × ϕ.
Time Difference (T.D): Time difference between the waves meeting at a point is given by T.D = T2 π×ϕ= T2 π×ϕ
Resultant Amplitude and Intensity
If we have two waves   y1= a1sin ω ty1= a1sin ω t  and  y2= a2sin( ω t+ϕ)y2= a2sin( ω t+ϕ) where  a1,a2=a1,a2= Individual amplitudes,  ϕ=ϕ=   Phase difference between the waves at an instant when they are meeting a point.     I1,I2=I1,I2=Intensities of Individual waves.
Resultant Amplitude:
After superimposition of the given waves resultant amplitude (or the amplitude of resultant wave) is given by  A=a12+a22+2a1a2cos−−−−−−−−−−−−−−−√ϕA=a12+a22+2a1a2cosϕ
For the interfering waves y1=a1sin ω ty1=a1sin ω tand y2=a2sin( ω t+ϕ)y2=a2sin( ω t+ϕ), Phase difference between them is 90o90o . So resultant amplitude A=a12+a22−−−−−−−√A=a12+a22
Resultant Intensity:  
As we know intensity  α (Amplitude)2 α (Amplitude)2 ⇒I1-ka12,I2-ka22 and I=kA2(k⇒I1-ka12,I2-ka22 and I=kA2(k  is a proportionality constant) . Hence from the formula of resultant amplitude, we get the following formula of resultant intensity
I-I1+I2+2I1I2−−−√cosϕI-I1+I2+2I1I2cosϕ
The term 2I1I2−−−√cosϕ2I1I2cosϕ  is called interference term. For incoherent interference, this term is zero so resultant intensity  I=I1+I2I=I1+I2.
You may also like: 

CBSE Term 2 Date Sheet Class 12
12th Board Exam Time Table 2022 Maharashtra
Rajasthan Board 12th Model Paper 2022
UP Board Time Table 2021-22 Class 12
CBSE Class 12 New Syllabus 2021-22

You can download the Wave Optics Class 12 Notes PDF by clicking on the link given below.