The graph shows the relationship between object distance (u) and image distance (v) for an equiconvex lens. The focal length of the lens is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 5.00 cm
Any one point of the \( u \)-\( v \) curve, put into the lens formula, gives the focal length. Point A, where the curve meets the dashed line \( v = -u \), is the easiest to read.
Readings at A (Cartesian sign convention, object on the left):
\( u = -10\,\mathrm{cm} \)
\( v = +10\,\mathrm{cm} \)
\( \displaystyle \frac{1}{f} = \frac{1}{v} - \frac{1}{u} = \frac{1}{10} - \frac{1}{(-10)} = \frac{2}{10} \)
\( \displaystyle f = 5.00\,\mathrm{cm} \)