Which of the following is NOT true?

The correct answer is Option (1) → The corpuscular model predicted that if a ray of light bends away from the normal on refraction, the speed of light would be greater in the second medium.

Option (1) The corpuscular model predicted that if a ray of light bends away from the normal on refraction, the speed of light would be greater in the second medium. — Not true. The corpuscular model predicted a greater speed in the second medium when the ray bends towards the normal. A ray bending away from the normal would, on that model, mean a smaller speed in the second medium.

Option (2) The wavelength of yellow light is about \( 0.6\,\mu\mathrm{m} \). — True. The measured wavelength of visible light is extremely small; for yellow light it is about \( 0.6\,\mu\mathrm{m} \) (600 nm).

Option (3) From the wave equation, Maxwell could calculate the speed of electromagnetic waves in free space, and he found that the theoretical value was very close to the measured value of the speed of light. — True. The speed \( 1/\sqrt{\mu_0\varepsilon_0} \) from Maxwell’s equations came out very close to the measured speed of light. This led to the conclusion that light is an electromagnetic wave.

Option (4) According to the wave model, the speed of light in water is less than the speed of light in air. — True. On the wave model, a wave that bends towards the normal on refraction travels more slowly in the second medium. Light entering water from air bends towards the normal, so it is slower in water, as Foucault’s experiment (1850) later confirmed.

NCERT (2026-27):
Introduction – “… The corpuscular model predicted that if the ray of light (on refraction) bends towards the normal then the speed of light would be greater in the second medium.”