Question

The focal lengths of the objective and eye-lens of a microscope are 1 cm and 5 cm respectively. If the magnifying power for the relaxed eye is 45, then the length of the tube is

• A. 30 cm
• B. 25 cm
• C. 15 cm
• D. 12 cm
  

Answer 1

The correct option is C 15 cm

Given that $f_0=1cm,f_e=5cm,m_{\infty }=45$
By using $m_{\infty }=\frac{(L_{\infty }-f_0-f_e)}{f_0{f}_e}\Rightarrow 45=\frac{(L_{\infty }-1-5)\times 25}{1\times 5}\Rightarrow L_{\infty }=15cm$