What is the focal length of a convex lens?

Answer and explanation;

-The focal length is the distance from the center of the lens to the principal focus (or focal points) of the lens. For a converging lens (for example a convex lens), the focal length is positive. On the other hand, the focal length of concave lens is negative.

Thus, for convex lens, the focal length is a distance over which all the parallel rays will converge. A certain point over that distance all the parallel rays will converge, that point is known as focal point.

c.the charges if the proton and electron and gravity

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.