A traveling wave is described by the equation $y(x, t) = [0.05 \sin (8x - 4t)]$ m
The velocity of the wave is [All the quantities are in SI unit]

The electric potential at the center of two concentric half rings of radii $R_1$ and $R_2$, having same linear charge density $\lambda$ is ($\epsilon_0$ = permittivity of free space)

If two charges $q_1$ and $q_2$ are separated with distance 'd' and placed in a medium of dielectric constant $K$. What will be the equivalent distance between charges in air for the same electrostatic force?

Two isolated metallic spheres of radii $R$ and $2R$ are charged such that both have the same charge density $\sigma$. The spheres are then connected by a thin conducting wire. If the new charge density of the larger sphere is $\sigma_1$. The ratio $\sigma_1$ to $\sigma$ is