Exams › NEET › Physics

The focal length of converging lens is measured for violet, green and red colours. It is respectively f_v, f_g, f_r. We will get

1. f_v < f_g < f_r
2. f_v > f_g > f_r
3. f_v = f_g = f_r
4. f_v > f_g < f_r

Correct answer: f_v < f_g < f_r

Solution

The focal length of a converging lens depends on the refractive index, which varies with wavelength. Since violet light has the shortest wavelength and red light has the longest, the refractive index is highest for violet and lowest for red. This results in f_v < f_g < f_r.

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 →