Exams › NEET › Physics

If f_v and f_r are the focal lengths of a convex lens for violet and red light respectively and F_v and F_r are the focal lengths of concave lens for violet and red light respectively, then we have

1. f_v < f_r and F_v > F_r
2. f_v > f_r and F_v < F_r
3. f_v > f_r and F_v > F_r
4. f_v < f_r and F_v < F_r

Correct answer: f_v < f_r and F_v > F_r

Solution

For a convex lens, the focal length for violet light (f_v) is shorter than for red light (f_r) due to greater refraction of violet light. For a concave lens, the focal length for violet light (F_v) is longer than for red light (F_r) for the same reason. Hence, the correct option is A.

Related NEET Physics questions

• An image formed by a plane mirror is:
• One face of a rectangular glass plate 6 cm thick is silvered. An object held 8 cm in front of the first face forms an image 12 cm behind the silvered face. The refractive index of the glass is
• Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 3/2 is
• A beam of monochromatic light is refracted from vacuum into a medium of refractive index 1.5, the wavelength of refracted light will be
• Green light of wavelength 5460 Å is incident on an air-glass interface. If the refractive index of glass is 1.5, the wavelength of light in glass would be (c = 3 × 10⁸ ms⁻¹)
• When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index.

⚔️ Practice NEET Physics free + battle 1v1 →