Two towers on top of two hills are $40 \, km$ apart. The line joining them passes $50 \, m$ above a hill halfway between the towers. What is the longest wavelength of radio waves (in $cm$),which can be sent between the towers without appreciable diffraction effects?

In a Fraunhofer diffraction pattern,the slit width is $0.5 \ mm$ and the screen is at $2 \ m$ away from the lens. If the wavelength of the light used is $5500 \ Å$,then the distance between the first minima on either side of the central maximum is (assume $\theta$ is small and measured in radians). (in $mm$)

In Fraunhofer diffraction,draw the graph of the intensity of light on the screen versus the diffraction angle $\theta$ and write its characteristics.

For what distance is ray optics a good approximation when the aperture is $3\; mm$ wide and the wavelength is $500\; nm$?

What do the Fraunhofer lines in the solar spectrum indicate?

In the Fraunhofer diffraction experiment, $L$ is the distance between the screen and the obstacle, $b$ is the size of the obstacle, and $\lambda$ is the wavelength of the incident light. The general condition for the applicability of Fraunhofer diffraction is: