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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 10 WAVE OPTICS

Newton’s corpuscular theory

Wave theory - nature of electromagnetic waves

Wave front

Huygens principle

Refraction of a plane wave from rarer to denser medium

Refraction of a plane wave from denser to rarer medium

Reflection of a plane wave by a plane surface

Behaviour of a plane wave front with different surfaces

The Doppler effect

Superposition principle

Coherent sources of light

Interference of light

Young’s double slit experiment

Fringe width in double slit experiment

Diffraction of light

Single slit experiment

Double slit vs single slit patterns

Interference vs diffraction due to single slit

Constraints for diffraction due to single slit

Viewing the diffraction pattern

Energy is conserved during interference and diffraction

When can we consider the light beam to be parallel beam in single slit experiment?

Resolving power of an objective lens

Fresnel distance

Polarisation

Polarisation by transmission

Polarisation by scattering

Polarisation by reflection - Brewster’s law

Law of Malus

Polaroid and uses of polaroids

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 10 WAVE OPTICS

Refraction of a plane wave from rarer to denser medium

Let PP’ represent the surface separating medium 1 and medium 2. Let v1 and v2 represent the speed of light in medium 1 and medium 2, respectively. Let us take a plane wave front AB, propagating in the direction A’A, incident on the interface at an angle i. If τ be the time taken by the wave front to travel the distance BC and BC = v1τ

???

By the time the point B on wave front travels to point C in medium 1, the point A would have travelled in medium 2, to E The new wave front will be CE and AE = v2τ.

Nowsini=BCAC=v1 andsinr=AEAC=v2   

 sini sinr=v1v2

This is Snell’s law.

If r < i then the ray bends toward the normal and the speed of the light wave in the second medium (v2) will be less than the speed of the light wave in the first medium (v1). This is correct and proves the corpuscular theory wrong.

The constants

n1 =cv1  and n2 =cv2 

are called refractive indices of medium 1 and 2 respectively.

Also,  n1sini= n2sinr

and,     v1v2=λ1λ2

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