A thin rod of length ' 4 L ' and mass ' 4 m ' is bent at the points as shown in the figure. The moment of inertia of the rod about an axis passing through point ' $O$ ' and perpendicular to plane of the paper is

The resistance of a coil for d.c. is $5 \Omega$. In a.c., the resistance will
When a ray of light is refracted from one medium to another, then the wavelength changes from $6000 \mathop {\rm{A}}\limits^ \circ$ to $4000 \mathop {\rm{A}}\limits^ \circ$. The critical angle for the interface will be
A pipe closed at one end vibrating in fifth overtone is in unison with open pipe vibrating in its fifth overtone. The ratio of $l_{\mathrm{c}}: l_{\mathrm{o}}$ is $\left[l_{\mathrm{c}}=\right.$ vibrating length of closed pipe, $l_0=$ vibrating length of open pipe]