Which part of the eye helps in changing the focal length of the eye lens to focus the image of objects lying at varying distances from the eye?

What color does a red rose appear when green light is incident upon it?

$A$ myopic person has been using spectacles of power $-1.00\, D$ for clear vision. During old age,he also needs to use separate reading glasses of power $+2.00\, D$. Explain what may have happened to his eyesight?

On what factor does the colour of the scattered light depend?

$A$ person suffering from an eye defect uses lenses of power $-1 \,D$. Identify the eye defect. Draw a suitable diagram to illustrate how this type of lens corrects the defect. Give the nature of the corrective lens to be used. Also,calculate the focal length of the corrective lens.

How does atmospheric refraction take place? Why do stars twinkle,but planets do not?