Question

The ratio of sizes of two images, obtained on a fixed screen of a candle for two positions of a thin lens (focal length f), is b. If distance between candle and screen is d(> 4f), then f is –

• A. $\frac { d } { \left( 2 + \sqrt { \beta } + \frac { 1 } { \sqrt { \beta } } \right) }$
• B. $\frac { d } { \left( \sqrt { \beta } + \frac { 1 } { \sqrt { \beta } } \right) }$
• C. $\frac { d } { \left( 1 + \sqrt { \beta } + \frac { 1 } { \sqrt { \beta } } \right) }$
• D. None of these

Answer 1

Answer: (A)

$\frac { d } { \left( 2 + \sqrt { \beta } + \frac { 1 } { \sqrt { \beta } } \right) }$

Answer 2

b = Ž x =$\left( \frac { \sqrt { \beta } - 1 } { \sqrt { \beta } + 1 } \right)$d and f =