Physics Circle home Student Login

Home›Chapters›Ray Optics PYQs›Combination of Lenses›Question 68

NEET 2016 (Phase 2) · Combination of Lenses

Combination of Lenses question from NEET 2016 (Phase 2)

Q68NEET 2016 · PHASE 2Medium

Combination of Lenses

Two identical glass (μ\mug = 3/2) equiconvex lenses of focal length ff each are kept in contact. The space between the two lenses is filled with water (μw=4/3)(\mu_w = 4/3). The focal length of the combination is

Show answer and solution

Answer: (d)

  1. Glass lens: 1f=12⋅2R⇒R=f\frac{1}{f} = \frac{1}{2} \cdot \frac{2}{R} \Rightarrow R = f
  2. Water forms a biconcave lens: 1fw=−13⋅2R=−23f\frac{1}{f_w} = -\frac{1}{3} \cdot \frac{2}{R} = -\frac{2}{3f}
  3. 1F=2f−23f=43f\frac{1}{F} = \frac{2}{f} - \frac{2}{3f} = \frac{4}{3f}
  4. So the answer is (d) 3f4\frac{3f}{4}.
Report a mistake

More questions on Combination of Lenses