A far sighted person can see object beyond 71cm clearly if separation between glasses and eye lens is 2cm, then find focal length of glass?
A
23cm
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B
69cm
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C
18.4cm
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D
30cm
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Solution
The correct option is B69cm v=71cm =0.71m; v=image distanceDistance between glass and eye =2cm=0.02mNow,Distance between image and eye =0.71-0.02=0.69mLets focal length be fv=-0.69(because left side is fo principle axis)