The fifth harmonic of a closed organ pipe is found to be in unison with the first harmonic of an open pipe. The ratio of lengths of closed pipe to that of the open pipe is $5 / x$. The value of $x$ is $\_\_\_\_$

In case of vertical circular motion of a particle by a thread of length $r$ if the tension in the thread is zero at an angle $30^{\circ}$ shown in figure, the velocity at the bottom point $(A)$ of the circular path is (g = gravitational acceleration)

The velocity $(v)$ - Distance $(x)$ graph is shown in figure. Which graph represents acceleration(a) versus distance ( $x$ ) variation of this system?

In the Young's double slit experiment the intensity produced by each one of the individual slits is $I_{\mathrm{o}}$. The distance between two slits is 2 mm . The distance of screen from slits is 10 m . The wavelength of light is $6000 \mathrm{~A}^{\circ}$. The intensity of light on the screen in front of one of the slits is $\_\_\_\_$