For better tuning of a series $L C R$ circuit in a communication system, the preferred combination is

The magnitude of the electric field of a plane electromagnetic wave travelling in free space is $E$. If $\mu_0$ and $\varepsilon_0$ are respectively permeability and permittivity of the free space, then the magnitude of magnetic field of the wave is

An alpha particle moves along a circular path of radius 0.5 mm in a magnetic field of $2 \times 10^{-2} \mathrm{~T}$. The de-Broglie wavelength associated with the alpha particle is nearly (Planck's constant $=6.63 \times 10^{-34} \mathrm{~J} \mathrm{~s}$ )

The difference between the frequencies of second and first Paschen lines of hydrogen atom is ( $R=$ Rydberg constant and $c=$ speed of light in vacuum)