Question

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Answer 1

ii) Thus the focal length of lens required for correctiom near vision is + 66. 7 cm. Plus sign of focal length tells us that it is convex lens.

Answer 2

Answer:

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Explanation:

(i)  $Power,P = -5.5 D , focal\:Length,f=?$

∵  $P=\frac{1}{f(in\:m)}$

$or\:-5.5=\:\frac{1}{f}$

$or\:f=\frac{1}{-5.5} =0.18m$

$The\:Negative\:(-)sign\:Indicates\:that\:the\:Lens\:is\:Concave$

$(ii) Power,P=+1.5D$

$Focal\:Length,f=?$

∵   $P=\frac{1}{f\:in\:m}$

$or\:+1.5=\frac{1}{f}$

$or\:f=\frac{1}{+1.5}$

$or\:f=+0.67$

$The\:positive\:sign\:indicates\:that\:the\:lens\:is\:Convex$