A ray of light is incident on first face of an equilateral glass prism at an angle of incidence ' $I$ '. The emergent ray just grazes along the adjacent face. The refractive index of the the prism is $\sqrt{2}$. The value of angle of incidence at first face is $\left(\sin 45^{\circ}=\frac{1}{\sqrt{2}}, \sin 90^{\circ}=1\right)$

In hydrogen atom, the energy of electron in first and third orbit is ' $E_1$ ' and' $E_3$ ' respectively. If $E_3=x E_1$ then the value of $x$ will be

Figure shows the north pole of a magnet moving away from a thick conducting loop containing a capacitor. The excess positive charge will arrive on

An observer moves towards a stationary source of sound with a velocity of one fifth of the velocity of sound. The percentage increase in the apparent frequency is