The ultraviolet spectrum can be divided into three regions based on wavelength: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). (a) Photons from which region have the highest energy and therefore are the most harmful to living tissue? (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm).

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Understand that the energy of a photon is inversely proportional to its wavelength. This means that shorter wavelengths correspond to higher energy photons.

Recall the formula for the energy of a photon: E = \( \frac{hc}{\lambda} \), where E is the energy, h is Planck's constant, c is the speed of light, and \( \lambda \) is the wavelength.

Identify the wavelength ranges for each UV region: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm).

Compare the wavelength ranges: UV-C has the shortest wavelengths, followed by UV-B, and then UV-A.

Conclude that UV-C photons have the highest energy due to their shortest wavelengths, making them the most harmful to living tissue.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Photon Energy and Wavelength

The energy of a photon is inversely related to its wavelength, as described by the equation E = hc/λ, where E is energy, h is Planck's constant, c is the speed of light, and λ is the wavelength. This means that shorter wavelengths correspond to higher energy photons. Understanding this relationship is crucial for determining which ultraviolet (UV) region is the most harmful.

Ultraviolet Radiation Regions

Ultraviolet radiation is categorized into three regions: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). Each region has different biological effects, with UV-C having the shortest wavelength and highest energy, making it the most harmful to living tissues. Recognizing these distinctions helps in assessing the potential risks associated with exposure to different UV wavelengths.

Biological Effects of UV Radiation

UV radiation can cause various biological effects, including DNA damage, skin burns, and increased risk of skin cancer. The severity of these effects is influenced by the energy of the UV photons, with higher energy photons (like those in the UV-C range) being more damaging. Understanding these effects is essential for evaluating the health risks associated with exposure to different UV regions.

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(b) Use the energy requirements of these two pro- cesses to explain why photodissociation of oxygen is more important than photoionization of oxygen at altitudes below about 90 km.

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Textbook Question

The wavelength at which the O₂ molecule most strongly absorbs light is approximately 145 nm. (a) In which region of the electromagnetic spectrum does this light fall?

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Textbook Question

The wavelength at which the O₂molecule most strongly absorbs light is approximately 145 nm. (b) Would a photon whose wavelength is 145 nm have enough energy to photodissociate O₂whose bond energy is 495 kJ/mol? Would it have enough energy to photoionize O₂?

Textbook Question

The ultraviolet spectrum can be divided into three regions based on wavelength: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). (b) In the absence of ozone, which of these three regions, if any, are absorbed by the atmo- sphere?

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Textbook Question

The ultraviolet spectrum can be divided into three regions based on wavelength: UV-A (315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). (c) When appropriate concentrations of ozone are present in the stratosphere, is all of the UV light absorbed before reaching the Earth’s surface? If not, which region or regions are not filtered out?