Question 7: Units , Dimensions and Error Analysis

Question

A symmetric double convex lens is cut into two equal parts by a plane perpendicular to the principal axis. If the power of the original lens is 4D, the difference between the powers of the original lens and the cut lens is

Accepted Answer

Original symmetric doubleÃ¢ÂÂconvex lens
Ã¢ÂÂ Radii: $R_1=R$, $R_2=-R$
Ã¢ÂÂ Power:
$$      \phi_{\rm orig}=(n-1)\Bigl(\frac1{R_1}-\frac1{R_2}\Bigr)      =(n-1)\Bigl(\frac1R-\frac1{-R}\Bigr)      =\frac{2(n-1)}{R}=4\;\rm D      $$
One half of the lens (planoÃ¢ÂÂconvex)
Ã¢ÂÂ Radii: $R_1=R$, $R_2=\infty$
Ã¢ÂÂ Power:
$$      \phi_{\rm half}=(n-1)\Bigl(\frac1{R}-\frac1\infty\Bigr)      =\frac{n-1}{R}      =\frac12\,\phi_{\rm orig}      =2\;\rm D      $$
Difference in power
$$    \phi_{\rm orig}-\phi_{\rm half}    =4\;{\rm D}-2\;{\rm D}    =2\;{\rm D}    $$
Answer: 2 D.

Answer

zero

Answer

3D

Answer

D

Answer

2D

Units , Dimensions and Error Analysis

A symmetric double convex lens is cut into two equal parts by a plane perpendicular to the principal axis. If the power of the original lens is 4D, the difference between the powers of the original lens and the cut lens is

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