Question

For a person sitting near a fire, why do the objects like trees and houses on the other side of the fire appear shifting?

Answer 1

1. We know that the refractive index is given by $\mu =\frac{c}{v}$ ……$\left(1\right)$ where $c$ is the velocity of light in a vacuum and $v$ is the velocity of light.
2. We also know that velocity $v$ is given by $v=f\lambda$ ……$\left(2\right)$ where $f$ is the frequency and $\lambda$ is the wavelength.
3. Substituting the value of $v$ in equation $\left(1\right)$ we get,

$\Rightarrow \mu =\frac{c}{f\lambda }$

$\Rightarrow \mu$∝$\frac{1}{\lambda }$

The refractive index is inversely proportional to wavelength.

The hot air around the fire rises up and cold air fills the space of hot air which creates a continuous and varying refractive index. So the light coming from objects behind fire pass through the region which refracts continuously. That's why objects on the other side appear like shifting.

Hence, the objects like trees and houses on the other side of the fire appear to shift because of continuous and varying refractive index.