TIME REMAIN
43:20
Roshan makes the table below to describe how to draw a ray diagram for a convex lens.
Ray from Object to Lens
Draw through the focal point on the
same side of the lens as the object.
Draw parallel with the main axis
After Passing Through Lens
The ray goes parallel to the main axis.
The ray goes away from the main axis as
though it came from the focal point near the
object
The ray goes straight through and does not
bend
Draw to the center of the lens
What error did Roshan make?
The ray that goes through the senter should bend and go through the focal point on the other side.
The ray that starts out parallel with the main axis should bend toward the axis and go through the focal point on the other
side.
The ray that goes parallel to the main axis after passing through the lens should also be parallel from the object to the lens.
The rays in the table describe how rays are drawn for a concave lens rather than for a convex lens.

here we know that ball will drop down by total distance 3.2 m

so here we know that

now using kinematics

now in the same time it will cover horizontal distance of 0.75 m

so speed of the ball will be

what is the speed of a softball that travels 20m in 2secs

speed = 20/2 = 10 m/s

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.