Chapter 21: Problem 4

Briefly explain why metals are opaque to electromagnetic radiation having photon energies within the visible region of the spectrum.

Short Answer

Expert verified

Metals are opaque to electromagnetic radiation within the visible region of the spectrum due to the interaction between the incident photons and the conduction electrons present in the metal. The conduction electrons can easily absorb the energy from the photons in the visible region since the energy gap between the valence and conduction bands in metals is small. This absorption process converts the photon energy into movement, primarily thermal energy, preventing the visible light from passing through the metal and resulting in the opacity of metals.

Step by step solution

Understand the properties of metals

In metals, the conduction electrons are free to move throughout the material. These electrons are responsible for the characteristic properties of metals, including their electrical conductivity and metallic luster.

Explain the interaction between conduction electrons and incident photons

When electromagnetic radiation (e.g., visible light) interacts with a metal, the incident photons interact with the conduction electrons present in the metal. Since the conduction electrons are free to move, they can absorb the energy from the incident photons. The probability of this absorption process depends on the energy of the incident photons.

Discuss the energy levels of conduction electrons

In metals, the conduction electrons occupy a continuous range of energy levels known as the conduction band. The energy gap between the valence band (where the electrons are tightly bound to their parent atoms) and the conduction band is very small or even nonexistent in metals.

Relate the energy of incident photons to the absorption process

The energies of photons within the visible region of the electromagnetic spectrum are in the range of 1.65 to 3.1 eV (electron volts). As the energy gap between the valence and conduction bands in metals is small, the conduction electrons can easily absorb photons with energies within the visible region.

Explain the opacity of metals

When the conduction electrons absorb the incident photons, they convert the energy into movement, mainly thermal energy. As a result, the visible light does not pass through the metal, making it opaque. The absorbed energy is also responsible for the reflection of light off the metal surface, giving metals their characteristic shiny appearance. In conclusion, metals are opaque to electromagnetic radiation with photon energies within the visible region of the spectrum due to the interaction between the incident photons and the conduction electrons, which absorb the energy and prevent the light from passing through the metal.

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Briefly explain why metals are opaque to electromagnetic radiation having photon energies within the visible region of the spectrum.

Short Answer

Step by step solution

Understand the properties of metals

Explain the interaction between conduction electrons and incident photons

Discuss the energy levels of conduction electrons

Relate the energy of incident photons to the absorption process

Explain the opacity of metals

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