Question

Indicate the region of the spectrum for each of the following wavelengths of light. (a) \(320 \mathrm{nm}\) (b) \(1500 \mathrm{nm}\)

Short answer

(a) Ultraviolet region; (b) Infrared region.

Step-by-step solution

Understanding the Electromagnetic Spectrum

The electromagnetic spectrum is the range of all types of electromagnetic radiation, which includes, from longest to shortest wavelengths: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Each region corresponds to specific wavelengths.

Identify the Region for 320 nm

A wavelength of 320 nm falls within the ultraviolet region of the spectrum. The ultraviolet range is typically between 10 nm to 400 nm.

Identify the Region for 1500 nm

A wavelength of 1500 nm falls within the infrared region of the spectrum. The infrared range typically spans from around 700 nm to 1 mm.

Key concepts

Wavelengths

Wavelengths refer to the distance between successive crests of a wave. In the context of light and the electromagnetic spectrum, wavelengths determine the type of electromagnetic radiation. The electromagnetic spectrum is a broad range of wavelengths and frequencies that include various types of radiation such as visible light, microwaves, and even radio waves.

Wavelengths are typically measured in nanometers (nm) when dealing with light. The visible light spectrum, which humans can see, spans from about 400 nm to 700 nm. Beyond these, wavelengths extend into other regions like infrared and ultraviolet, which are not visible to the human eye. These various regions are essential in different applications, from medical imaging to communication technologies.

Understanding wavelengths and their corresponding regions helps in identifying what type of electromagnetic radiation you are dealing with, which is crucial in scientific and practical applications.

Ultraviolet Region

The ultraviolet (UV) region of the electromagnetic spectrum lies just beyond the violet end of the visible light range. UV wavelengths typically range from about 10 nm to 400 nm. This region of the spectrum is known for its high energy and is categorized into several sub-bands, including:

• UVA (320-400 nm): These are the longest UV wavelengths and are less harmful. They are commonly used in black lights and tanning beds.
• UVB (280-320 nm): These wavelengths can cause sunburn and are partially absorbed by the ozone layer.
• UVC (100-280 nm): These have the shortest wavelengths and highest energy, making them the most harmful. They are absorbed completely by the Earth's atmosphere.

Ultraviolet light has practical uses in sterilization and disinfection due to its energy, which can destroy the DNA of bacteria and viruses. While it has beneficial applications, excessive exposure to UV rays can be harmful, leading to skin damage and other health issues.

Infrared Region

The infrared (IR) region sits just beyond the red end of the visible light spectrum, spanning from approximately 700 nm to 1 millimeter. The IR spectrum is known for its longer wavelengths compared to visible light and is divided into several parts based on wavelength:

• Near-infrared (700 nm - 1400 nm): Used in telecommunications and remote controls.
• Mid-infrared (1400 nm - 3000 nm): Found in various sensors and used for chemical analysis.
• Far-infrared (beyond 3000 nm): Often used in thermal imaging and heat sensing technologies.

Infrared light is primarily associated with heat, as objects that are warm emit radiation in this region. This is why thermal cameras, which detect IR radiation, can visualize heat patterns and are used in applications like night vision, wildlife observation, and medical diagnostics.

Understanding the infrared region's properties and applications is critical in areas such as environmental monitoring and in industries where heat and energy efficiency are paramount.