Ultraviolet light, associated energy

Franck and Gustav Hertz passed electrons through mercury vapor at low pressure to determine the minimum kinetic energy required to produce the excited state that emits ultraviolet light at 253.7 nm. What is that minimum kinetic energy What wavelength is associated with electrons of this energy ... 

Stilbene is a molecule which exists in two isomeric states because of the large energy barrier associated with rotation around the central double bond (see fig. 7.13). It has been known for some time [22] that when stilbene is excited to its first singlet state by absorption of UV light, it rapidly fluoresces to the ground state but with some molecules in the other isomeric form. Thus, if c -stilbene is irradiated with ultraviolet light, one obtains approximately 50% tran -stilbene and... 

The word radiant energy is the energy transmitted from one body to another in the form of radiations. This energy has wave nature and because it is associated with electric and magnetic fields, it is also called electro-magnetic radiations. The visible light, ultraviolet, infrared, X-rays, radio-waves and microwaves are all different forms of electromagnetic radiations. 

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