Question

Suppose you have a bright source of ultravi- olet light. The light is invisible to your eye, but when you shine the beam from the source onto your shirt, the white part of the shirt glows brightly in visible light. What is this process called, and what is going on?

1. Frequency doubling. It happens in molecules that are very unsymmetric.

2. Forbidden emission. The absorbed pho- tons can’t escape unless they split in two.

3. Stimulated emission. The ultraviolet pho- tons are knocking photons of visible light out of the material.

4. Fluorescence. Atoms or molecules are absorbing photons of high kinetic energy and emitting photons of lower kinetic energy.

5. Phosphorescence. Photons are stored in the shirt atoms for a while, but eventually escape.

Answer 1

In general, Fluorescence takes place as light is absorbed at one energy and part of the energy is re-emitted at longer wavelengths. In the case of visible light is re-emitted, ultraviolet light has been absorbed.

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Fluorescence. Atoms or molecules are absorbing photons of high kinetic energy and emitting photons of lower kinetic energy.

Correct option is (4)