If a person uses a lens of -2.5 D power, then the focal length of the lens is ……………………

Correct option is  C) 2f

Correct option is  B) double

Correct option is  A) 20 cm

Correct option is  C) 40 cm

Correct option is  B) 50 cm

Correct option is  A) 25cm

Correct option is  A) 2.27 cm

Correct option is  A) 40 cm

 U = -12 f = -10  1/v - 1/u = 1/f 1/v + 1/12 = 1/10 1/v = 1/60  \(-\frac{1}{v^2} \)dv or \(\frac{1}{u^2} \)du du = \(\frac{v^2}{u^2} \)du \( \frac{v}{u} \)= same path △u1 = △u2 = 1mm △u1 = △v2  △v2 = vf - vi  x2 = △v2 + 1mm x2...

Correct option is C) 20 cm