A body is suspended from a string of length 1 m and mass 2 g. The mass of the body to produce a fundamental mode of 100 Hz frequency in the string is (Acceleration due to gravity $$=10 \mathrm{~ms}^{-2}$$)
Electrostatic force between two identical charges placed in vacuum at distance of $$r$$ is F. A slab of width $$\frac{r}{5}$$ and dielectric constant 9 is inserted between these two charges, then the force between the charges is
A ray is incident from a medium of refractive index 2 into a medium of refractive index 1. The critical angle is
An electric dipole with dipole moment $$5 \times 10^{-7} \mathrm{C}-\mathrm{m}$$ is in the electric field of $$2 \times 10^4 \mathrm{NC}^{-1}$$ at an angle of $$60^{\circ}$$ with the direction of the electric field. The torque acting on the dipole is