Question

Please give me answer of question no. 6

Answer 1

he is suffering from myopia

concave lens

its focal length would be -ve

Answer 2

Part - A

A white light when passes through a prism gets diffused in a band of 7 colours called spectrum.

Violet colour deviates the most while Red deviates the least.

If a second identical prism is placed inverted the beam of light which was diffused in 7 colours would reappear after the second prism as the refractions of the 7 lights is inversed by the inverted prism which therefore deviates at the same angle as they had deviated in first prism in opposite direction and hence give a straight white beam of light.

Part - B

Defect -Myopia(short - sightedness)

Nature of lens - concave lens (because of the -ve sign in power)

Focal length of lens - 2mtrs.

we know , P=1/f

by putting values,

0.5=1/f

f=1/0.5=10/5=2mtrs.

Causes of defect-

1) elongation of eye ball

2) decrease in focal length of lens.