Give one cause of near-sightedness (myopia).

Why do we observe the seven colours when white light passes through a glass prism? Which component of white light deviates the least?

$(i)$ What is meant by dispersion of white light? Draw a diagram to show the dispersion of white light by a glass prism.
$(ii)$ Light of two colours $A$ and $B$ pass through a prism. $A$ deviates more than $B$ from its path of incidence. Which colour has a higher speed in the prism?

$A$ person cannot see distinctly objects kept beyond $2\, m$. This defect can be corrected by using a lens of power ........ $D$.

$A$ beam of white light falling on a glass prism gets split up into seven colours marked $1$ to $7$ as shown in the diagram. $A$ student makes the following statements about the spectrum observed on the screen.
$(a)$ The colours at position marked $3$ and $5$ are similar to the colour of the core of a hard-boiled egg and the colour of the sky respectively. Is the statement made by the student correct or incorrect? Justify.
$(b)$ Which of the two positions correspond closely to the colour of $(i)$ a solution of potassium permanganate,$(ii)$ danger or stop signal lights?

For a person suffering from myopia,the image of the object is formed in front of the retina.