Which of the following are the primary colours of light?

Draw ray diagrams each showing $(i)$ myopic eye and $(ii)$ hypermetropic eye.

The far point of a myopic person is $150 \ cm$ in front of the eye. Calculate the focal length and the power of a lens required to enable him to see distant objects clearly.

$A$ 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?

What is the far point of a person with normal vision?

Which two colors of light combine to form the color maroon?