Snells Law


 
 
Concept Explanation
 

Snells Law

This law say that the ratio of sine of angle of incidence to the sine of angle of refraction is constant for a pair of media i.e

frac{sin;i}{sin;r}= constant(_1eta_2 )

where  large _1eta_2 is the refractive index of the medium 2 w.r.t. medium 1.

Application of Snell's Law:

Ray Falling Perpendicular to Surface:

The ray which falls perpendicular to the refracting surface goes into the second medium undeviated.. This phenomenon can be explained with the help of Snell's law. As the ray is falling perpendicularly so the angle of incidence is 0

angle ;i = 0^0

From Snell's law we get

frac{sin;i}{sin;r}= constant(_1eta_2 )

sin;r= frac{sin;i}{_1eta_2 }

Now sin;i= sin;0^0 = 0

So sin;r= frac{0}{_1eta_2} = 0

sin;r= sin; 0^0

Rightarrow r = 0^0

As the angle of refraction is 0 so the ray goes without deviation.

Optically Denser and Rarer Medium:

In the pair of transparent medium, the medium that has a higher refractive index is called a denser medium and the other is called a rarer medium.

When light passes from rarer to denser medium it slows down  and bends toward the normal as shown in the figure R denotes rarer medium and D denotes denser medium.

Using Snells law:

eta _1;sin;theta_1 =eta _2;sin;theta _2 Rightarrow frac{sin;theta _1}{sin;theta _2}=frac{eta _2}{eta _1}

As the ray is moving from optically rarer medium to optically denser medium so

 large eta _2> eta _1

Angles are inversely proportional to refractive index, we get

 large theta _2< theta _1

Hence light bends towards the normal

When light passes from denser to rarer medium the speed increases and it bends away from the normal as shown in the figure R denotes rarer medium and D denotes denser medium.

Using Snells law:

eta _1;sin;theta_1 =eta _2;sin;theta _2 Rightarrow frac{sin;theta _1}{sin;theta _2}=frac{eta _2}{eta _1}

As the ray is moving from optically denser medium to optically rarer medium so

 large eta _2< eta _1

Angles are inversely proportional to refractive index, we get

 large theta _1< theta _2

Hence light bends away from the normal

Light Propagating Through A series of Different Medium:

When light propagates through a series of layer of different medium, then 

mu _1sinphi _1=mu _2sinphi _2=mu _3sinphi _3=..........=constant

Proof: Let us take the case of three layers of Medium 1 with refractive index  eta_1, Medium 2 with refractive index  eta_2 , Medium 3 with refractive index  eta_3 and Medium 4 with refractive index  eta_4 as shown in the figure below

Case I : Light rays goes from medium 1 to medium 2 where angle of incidence is phi_1 and angle of refraction is phi_2. Then according to Snell's law

frac{sin; phi_1}{sin;phi_2}= frac{eta_2}{eta_1}

Rightarrow ;;eta_1 times sin; phi_1= eta_2 times sin;phi_2                                ........[ I ]

Case II : Light rays goes from medium 2 to medium 3 where angle of incidence is phi_2 and angle of refraction is phi_3. Then according to Snell's law

.... (More Text Available, Login?)
 
Video Link - Have a look !!!
 
Language - Hindi/English
 
 
 
Related Videos
Language - Hindi/English
Language - Hindi/English
Language - Hindi/English

Language - Hindi/English
Language - Hindi/English
Language - Hindi/English

Language - Hindi/English
Language - Hindi/English
Language - Hindi/English

Language - Hindi/English


Students / Parents Reviews [20]