AIIMS 2018 Physics Lens Formula MCQ Question

To find the focal length of the contact lens (f₂) needed to achieve a combined focal length (f) of 2.5 cm with the human eye's focal length (f₁) of 2 cm, we use the lens formula for combined lenses:

$$\frac{1}{f} = \frac{1}{f₁} + \frac{1}{f₂}$$

Substituting the values, we get:

$$\frac{1}{2.5} = \frac{1}{2} + \frac{1}{f₂}$$

Solving this gives $f₂ = -10 \, \text{cm}$, indicating a diverging lens is required. Options A, B, and D are incorrect as they provide positive or incorrect negative focal lengths that do not satisfy the equation for the desired combined focal length.