Question

A ray of light travelling in air have wavelength $\lambda$ , frequency n , velocity v and intensity I. If this ray enters into water then these parameters are ${\lambda} $' n ' , v ' and I' respectively. Which relation is correct from following?

• A. $\lambda= {\lambda} ' $
• B. n=n '
• C. v=v'
• D. I = I'

Answer 1

The Correct Option is B

The question addresses how the properties of a light wave change as it transitions from one medium (air) to another (water). Let's examine each parameter systematically:

1. Frequency (n): The frequency of light is determined solely by the source and remains constant regardless of the medium it travels through. This is a fundamental principle of wave mechanics. Therefore, in both air and water, the frequency remains unchanged, leading to the correct relationship: n = n'.
2. Wavelength (\(\lambda\)): The wavelength of light changes when it enters a different medium due to the change in speed. In a medium like water, the velocity of light is reduced, leading to a shorter wavelength. The relation in another medium is given by: \(\lambda' = \frac{\lambda}{\text{Refractive Index}}\), indicating that the wavelength is not equal in different media.
3. Velocity (v): The speed of light is slower in water compared to air because water has a higher refractive index. Hence, v \neq v'.
4. Intensity (I): The intensity of light generally decreases when light travels from a less dense to a denser medium due to partial reflection and absorption. Thus, I \neq I'.

In conclusion, the only relationship that holds true when light transitions from air to water is that the frequency remains constant. Therefore, the correct answer is n = n'.