How can the formation of images be visualised ?

Q: How can the formation of images be visualised ?

Ans: Images can be visualised by drawing ray diagram. Some of the rays to be used to draw a ray diagram are listed:

(i) A ray parallel to the principal axis passes through the principal focus (or appears to diverge from the principal focus) after reflection.

(ii) A ray passing through the principal focus becomes parallel to the principal axis after reflection.

(iii) A ray passing through the centre of curvature of the mirror retraces its own path.

(iv) A ray incident at the pole is reflected with equal inclination to the principal axis.

What is accommodation of the eye ?

Q: What is accommodation of the eye ?

Solution:
The ciliary muscles contract and relax to change the over all focal length of the eye lens so that sharp images of the objects at different distances are formed on the retina. This process of adjustment of the focal length of the eye-lens is called accommodation.

Why stars seem higher than they actually are ?

Q: Why stars seem higher than they actually are ?

Sol:
due to atmospheric refraction, the stars seem to be higher than they actually are, light coming from a star is refracted as it leaves space and enters the earth’s atmosphere. Higher up in the sky air is rarer and nearer the earth’s surface is denser. Due to this refraction, the star appears to be a higher position.

Why sun looks red at time of sunrise and sunset ?

Q: Why sun looks red at time of sunrise and sunset ?

Sol: Light from the sun near the horizon passes through thicker layers of air and larger disgrace in the earth’s atmosphere before reaching our eyes. However in the overhead position. Light from the sun travel relatively shorter disgrace. At noon, the sun appears white as only a little of the blue and violet colours are scattered. At the time of sunset and sunrise (near the horizon), most of the blue light and shorter wavelengths are scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelengths. Hence the sun looks red both at time of sunrise and sunset.

Why sky looks blue ?

Q: Why sky looks blue ?

Sol: Blue colour of sky is due to scattering of sunlight. Light from the sun, while traveling through earth’s atmosphere gets scattered by large number of molecules in the earth’s atmosphere. The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelength. As the blue colour has shorter wavelength than red, therefore, blue colour is scattered much more strongly. Hence the sky looks blue.