Name the part of the human eye that helps in changing the focal length of the eye lens.

Study the diagram and answer the questions that follow:
$(i)$ Identify the defect of vision represented by this diagram.
$(ii)$ List the two possible causes of this defect.
$(iii)$ With the help of a ray diagram,explain how this defect can be corrected.

What is the range of clear vision for a person with normal vision?

Name the part responsible for the power of accommodation of the eye.

What is astigmatism?

Which of the following are the primary colours of light?