CBSE Class 12 Physics Optics chapter notes and important questions

CBSE Class 12 Physics Optics chapter notes and important questions. There are many more useful educational material which the students can download in pdf format and use them for studies. Study material like concept maps, important and sure shot question banks, quick to learn flash cards, flow charts, mind maps, teacher notes, important formulas, past examinations question bank, important concepts taught by teachers. Students can download these useful educational material free and use them to get better marks in examinations.  Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

 OPTICS

RAY OPTICS

GIST

1. REFLECTION BY CONVEX AND CONCAVE MIRRORS. 

a. Mirror formula 1/v+1/u=1/f where u is the object distance, v is the image distance and f is the focal length.

b. Magnification m=-v/u=f-v/f=f/f-u. m is -ve for real images and +ve for virtual images.

2. REFRACTION

c. Ray of light bends when it enters from one medium to the other, having different optical densities.

d. Sun can be seen before actual sunrise and after actual sunset due to Atmospheric refraction

e. An object under water ( any medium ) appears to be raised due to refraction when observed inclined

_{n=REAL DEPTH/APPRENT DEPTH}

and Where in reparative index of medium shift in the position (apparent) of object is X = t {1 – 1/n) where t is the actual depth of the medium

f. Snell’ s law states that for a given colour of light, the ratio of sine of the angleof incidence to sine of angle of refraction is a constant, when light travels from rarer to denser, sin ir/sin r=n₁/n₂

g. Absolute refractive index is the ratio between the velocities of light in vacuum to the velocity of light in medium. For air n=1 n= C/v 

3. h. When a ray of light travels from denser to rarer medium and if the angle of incidence is greater than critical angle, the ray of light is reflected back to the denser medium. This phenomenon is called Total internal reflection. sinC=n_R/n_D

i. Diamond has a high refractive index, resulting with a low critical angle (C=24.40). This promotes a multiple total internal reflection causing its brilliance and luster. Some examples of total interna reflection are formation of mirage and working of an optical fiber.

4. When light falls on a convex refracting surface, it bends and the relation between U, V and R is given by n₂/V-n₁/u=n₁-n₂/R

5. Lens maker’s formula or thin lens formula is given by 1/f=(n₂-n₁/n₁) (1/R₁-1/R₂)For Convex Lens R1 +ve ;R2 –ve Concave lens R1-ve; R2 +ve The way in which a lens behaves as converging or diverging depends upon the values of nL and nm.

6. When two lenses are kept in contact the equivalent focal length is given by

7. The lens formula is given by 1/V-1/u=1/f

8. When white light (poly chromatic or composite) is passed through a glass prism, It splits up into its component colours (Monochromatic). This phenomenon is called Dispersion.

9. Rainbow is formed due to a combined effect of refraction and total internal reflection of sunlight by spherical water droplets of rain.

10. Scattering of light takes place when size of the particle is very small when compared to the wavelength of light Intensity of scattered light is I α 1/λ⁴

The following properties or phenomena can be explained by scattering.

(i) Sky is blue.

(ii) Sky is reddish at the time of sunrise and sunset

(iii) Infra-red photography used in foggy days.

(iv) Orange colour of black Box

(v) Yellow light used in vehicles on foggy days.

(vi) Red light used in signals.

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