In the network shown cell E has internal resistance $r$ and the galvanometer shows zero deflection. If the cell is replaced by a new cell of emf $2 E$ and internal resistance $3 r$ keeping everything else identical, then

In hydrogen emission spectrum, for any series, the principal quantum number is $n$. Corresponding maximum wavelength $\lambda$ is ( $R=$ Rydberg's constant)

$\left[\mathrm{L}^2 \mathrm{M}^1 \mathrm{~T}^{-2}\right]$ are the dimensions of

For formation of beats, two sound notes must have