Why does light, like sound, not cross the walls?

2000/03/22 Elhuyar Zientzia

• Fisika

Sound and light are waves, but they are very different waves.

Sound is a mechanical wave, that is, it needs matter to propagate: if a blow occurs on the table, the sound (that is, the mechanical wave) occurs and the air molecules that are next to the table begin to vibrate. These molecules will simultaneously transmit the vibration to the neighbours, and these to the neighbours and thus to the ear. When the sound wave reaches a wall, the atoms of the wall behave like molecules of air and the sound, passing from one atom to another, reaches the other side of the wall. There, on the other side of the wall, the vibration will return to the air molecules and finally to the ear.

Light, for its part, is an electromagnetic wave, that is, a magnetic field and an electric field that move simultaneously, and does not need matter to propagate. Therefore, when it reaches the wall, the wave will be reflected or absorbed, but it will not pass to the other side.

When we say light we always speak of visible light, i.e. low energy wave within the entire spectrum of light. But there are rays of light of great energy, such as x-rays or gamma rays, that can pass through this matter.