Question

The equivalent focal length of a combination of two thin lenses (having focal length f₁& f₂) can be given by 1/f_net= 1/f₁ + 1/f₂ . If errors in measurement of f₁& f₂ are ± 0.5 cm and ± 0.3 cm and given that f₁ = f₂ . Then errors in equivalent focal length is –

• A. ± 0.1
• B. ± 0.8
• C. ± 0.2
• D. None

Answer 1

Answer: (C)

± 0.2

Answer 2

$\frac{\Delta f_{net}}{{f_{net}}^{2}}$= $\frac{\Delta f_{1}}{f_{1}^{2}} + \frac{\Delta f_{2}}{f_{2}^{2}}$