JAMB - Physics (2010 - No. 19)
The sound of an electricity bell dies down slowly when air is slowly pumped out from a bottle because
the wavelength of sound becomes greater in the bottle
sound cannot pass through the bottle
sound needs a material medium
sound can pass through a vacuum
解释
Sound wave requires a material medium for its propagation. so when air is being pumped out the density of the medium is being reduced and the sound dies down. when all the air has been pumped out of the glass, no sound will be heard, as sound sound cannot travel through vacuum