The ability of electromagnetic waves to pass through a material depends on various factors, including the nature of the material and the wavelength of the waves. In the case of infrared (IR) waves and microwaves, although microwaves have longer wavelengths compared to IR waves, they can still be more penetrating due to a phenomenon called resonance.
Resonance occurs when the frequency of the electromagnetic waves matches the natural frequency of the molecules in a material. In the case of microwaves, their frequencies are close to the natural frequency of water molecules. Water molecules are polar, meaning they have a positive and negative charge separation, which allows them to align with the oscillating electric field of microwaves.
When microwaves interact with water molecules, the molecules tend to rotate and generate heat through molecular friction. This interaction is the basis for the heating effect of microwaves in food and liquids. Because of this resonance and the ability of water molecules to absorb and convert microwave energy into heat, microwaves can penetrate deeper into materials that contain water molecules.
On the other hand, infrared waves do not resonate strongly with water molecules and other substances in the same way microwaves do. Infrared radiation can still be absorbed by certain materials, such as glass, which may contain atoms or molecules that vibrate at similar frequencies to those of the infrared waves. However, compared to microwaves, infrared waves generally have less penetrating power because they are not as efficient at exciting molecular vibrations or rotations.
It's important to note that the ability of electromagnetic waves to pass through materials is not solely determined by wavelength but also by the specific properties of the material and the interaction mechanisms involved.