KCET · Physics · Electromagnetic Induction
Calculate the focal length of a reading glass of a person if his distance of distinct vision is \( 75 \) \( \mathrm{cm} \).
- A \( 25.6 \mathrm{~cm} \)
- B ○ \( 37.5 \mathrm{~cm} \)
- C \( 75.2 \mathrm{~cm} \)
- D \( 100.4 \mathrm{~cm} \)
Answer & Solution
Correct Answer
(B) ○ \( 37.5 \mathrm{~cm} \)
Step-by-step Solution
Detailed explanation
Given, \( v=-75 \mathrm{~cm} ; u=-25 \mathrm{~cm} \).
Using \( \frac{1}{f}-\frac{1}{v}-\frac{1}{u} \), we get
\( \frac{1}{f}=\frac{1}{-75}-\frac{1}{-25}=\frac{-1+3}{75}=\frac{2}{75} \)
Therefore \( f=\frac{75}{2}=37.5 \mathrm{~cm} \)
Thus, focal length of reading glass is \( 37.5 \mathrm{~cm} \).
Using \( \frac{1}{f}-\frac{1}{v}-\frac{1}{u} \), we get
\( \frac{1}{f}=\frac{1}{-75}-\frac{1}{-25}=\frac{-1+3}{75}=\frac{2}{75} \)
Therefore \( f=\frac{75}{2}=37.5 \mathrm{~cm} \)
Thus, focal length of reading glass is \( 37.5 \mathrm{~cm} \).
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