12th Notes

Important points on refraction of light.

In this note we will discuss about the very important points on the refraction of light , every students must keep it in the mind . It is use ful for objective point of view.

Keep in your mind-

Some important thing for refraction of light.

1. Refractive index  µ=c/v where c is the velocity of light in air or vacuum and v is the velocity of light in given medium.

2. The speed of light in air slightly less than the speed of light in vacuum.

3.  The medium having greater refractive index is called denser and the other is rarer.

4. While going from a denser medium to rarer medium , the refracted ray bends away from the normal and vice-versa.

5. Snell’s low states that  µ = sin I /sin r { µ>1 if light moves from rarer to denser and µ<1 if light moves from denser to rarer.}.

6. As we know 1µ2= v1/v2 ,

Therefore , 1µ2 x  2µ1=[v1/v2 x v2/v1]=1

Or ,

 1µ2=1/ 2µ1 .

Similarly, 1µ2 x 2µ3x  3µ4 x…………..=1.

7. Laws of refraction is valid for all types of surface separating for two media i.e. the separating may be plane or curved.

8. The angle of deviation on refraction is given as ‘ angle of deviation’ =|i-r|.

9. If incident ray is normal, refraction takes place without bending. In this case I = r = 00.

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10. On refraction both the velocity as well as the wavelength of light changes but frequency and the phase doesn’t change.

11. rareµdenser >1 and  denserµrare< 1.

12. The value of refractive index depends on’

(a) the nature of two media (b) the colour or wavelength of the light (c)the temperature of the media.

13.As we know the value of refractive index is given as µ= sin I /sin r. but it doesn’t depend on the value of I, for a given pair of media.

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14. Refractive index has no dimension or unit.

15. Optical path is the distance travelled by light in vacuum in the same time travel in which it has travelled a distance x in a medium of refractive index µ . i.e. optical path = ct =cx/v=µx.

16 According to Cauchy’s formula, refractive index µ= A+ B/(wavelength)2.

Having saw this result we can say that, as wavelength increases refractive index decreases and vice-versa.

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