In the diagram, the total electric flux through the closed surface ' S ' is
[Given $\mathrm{q}=$ charge
$\varepsilon_0=$ permittivity of free space]
If an electron in hydrogen atom jumps from $3^{\text {rd }}$ orbit to $2^{\text {nd }}$ orbit it emits a photon of wavelength ' $\lambda$ '. When it emits a photon from $4^{\text {th }}$ orbit to $3^{\text {rd }}$ orbit then the corresponding wavelength of emitted photon will be
A solenoid having 400 turns/metre has a core of a material with relative permeability 300 . If a current of 0.5 A is passed through it, then the magnetisation of the core material is nearly
The volume of a block of metal at $30^{\circ} \mathrm{C}$ changes by $0.12 \%$ when its temperature is increased to $70^{\circ} \mathrm{C}$. The coefficient of linear expansion of the metal is