Taking the wavelength of first Balmer line in hydrogen spectrum (n = 3 to n = 2) as 660 nm, the wavelength of the 2nd Balmer line (n = 4 to n = 2) will be :

The magnetic field of a plane electromagnetic wave is given by :
$$$\overline B = {B_0}\widehat i\left[ {\cos (kz - \omega t)} \right] + {B_i}\widehat j\cos (kz + \omega t)$$$ B₀ = 3 × 10^–5 T and B1 = 2 × 10^–6 T.
The rms value of the force experienced by a stationary charge Q = 10^–4 C at z = 0 is closest to :

A uniform cable of mass 'M' and length 'L' is placed on a horizontal surface such that its (1/n)^th part is hanging below the edge of the surface. To lift the hanging part of the cable upto the surface, the work done should be :

A stationary horizontal disc is free to rotate about its axis. When a torque is applied on it, its kinetic energy as a function of $$\theta $$, where $$\theta $$ is the angle by which it has rotated, is given as k$$\theta $$². If its moment of inertia is I then the angular acceleration of the disc is :