Sound waves are travelling in a medium whose adiabatic elasticity is ${\mathrm{E}}_{\mathrm{H}}$ and isothermal elasticity is $\mathrm{E}$. The velocity of sound waves is proportional to

When a source of sound wave and an observer approach each other in static air medium, then the wavelength of sound wave appears to the observer to

The velocity of sound waves of frequency 200 vibrations per second at a place in the air medium when compared with the velocity of sound waves of frequency 400 vibrations per second is