Two lenses A and B have power of (i) + 2 D and (ii) -4D respectively. What is the nature and focal length of each lens?
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$\text{P}_\text{A}=+20$$\text{f}_\text{A}=\frac{1}{\text{P}_\text{A}}=\frac{1}{2}=+0.5\text{m}=+50\text{cm}$
Lens A is a convex lens.
$\text{P}_\text{B}=-4\text{D}$
$\text{f}_\text{B}=\frac{1}{\text{f}_\text{B}}=\frac{1}{-4}=-0.25\text{m}=-25\text{cm}$
Lens B is a concave lens.
Lens A is a convex lens.
$\text{P}_\text{B}=-4\text{D}$
$\text{f}_\text{B}=\frac{1}{\text{f}_\text{B}}=\frac{1}{-4}=-0.25\text{m}=-25\text{cm}$
Lens B is a concave lens.
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