Question

A 7m high partition wall in a room 10m high separates two students. Though both light and sound waves can bend around obstacles, how is that students are unable to see each other even though they can converse easily.

Answer 1

we know from concepts of diffraction,
$sin\theta=\frac{\lambda}{D}$

where $\theta$ is angle made by light after diffraction through obstacle or aperture, $\lambda$ is wavelength of light and D is the diameter of aperture.

for getting large value of angle made by light after diffraction through aperture, diameter of aperture should be comparable to the wavelength of light .

but here diameter of aperture, D = 10m
and wavelength of light , $\lambda$ = 10^-7 m

so, $sin\theta=\frac{10^{-7}}{10}\approx0$

hence, light goes almost unbent. that's why the students are unable to see each other even though they can converse easily.