$(a)$ Why does the stage of an auditorium have a curved background,curtains,carpets,and a false ceiling?
$(b)$ The sound of a ringing bell inside a vacuum chamber cannot be heard. Why?

(N/A) The curved background is designed to act as a reflector,ensuring that sound waves are directed and distributed uniformly throughout the auditorium. Curtains,carpets,and false ceilings are sound-absorbing materials used to minimize reverberation and prevent the formation of echoes,thereby improving the clarity of sound.
$(b)$ Sound is a mechanical wave that requires a material medium (such as air,water,or solids) to travel. Since a vacuum chamber contains no particles to transmit the vibrations of the bell,the sound cannot propagate,and therefore,it cannot be heard.