Every colour travels with the same speed in a transparent medium.

Which optical phenomenon is responsible for the formation of a rainbow?

Which phenomenon is responsible for the blue color of the clear sky?

In the dispersion of white light by a prism,which color of light undergoes the minimum deviation?

How many times is the wavelength of red light compared to the wavelength of blue light (in $\times$)?

$A$ student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw a ray diagram for the correction of this defect.