# Electromagnetic Spectrum Activity - Ultraviolet

## Resources

Ultraviolet light is much more than the sunburn it gives you. Ultraviolet light has more energy than visible light but less than x-rays. Most ultraviolet light is non-ionizing radiation. Ionizing radiation has enough energy to tear electrons away from their atoms. The atoms are now 'ions'. These ions can cause unwanted chemical reactions in a material or organism. The higher frequency UV which has shorter wavelengths is considered ionizing.

With shorter wavelengths it is more common to refer to the wave's wavelength rather than its frequency. Ultraviolet light covers the range from 10nm to 400 nm (nm = nanometers = 1x10-9). The frequency would be expressed in Phz (Petahertz). A high frequency wave has a short wavelength. The relationship is defined as:

• Variables:   λ=wavelength (m)     v = speed of light (3 x 108 m/s)     f = frequency (Hz). Note PHz = 1 x 1015
• Formula:   λ = v ÷ f
• Example:   λ = 3 x 108 m/s ÷ 3 PHz = 100 nm

Natural sources of UV include stars like our sun. Humans make UV in fluorescent tubes, UV LEDs and when electric arc welding. UV will damage your eyes unbeknownst to the viewer. Always use the proper eye protection, for example welder's goggles. Regular sunglasses are not sufficient!

We use the high energy of UV to sterilize objects such as the eye protection goggles. Some chemicals will fluoresce in ultraviolet light. The chemicals absorb the energy of the UV and release the energy at a longer wavelength - in the visible light band. This is how black light posters work. Our eyes do not detect the short wavelength UV but readily see the visible erupting like magic from the glowing poster. This same idea is used to detect counterfeit documents and some minerals .

In nature, some animals can see ultraviolet. Flowers may provide bees with nectar guides . A plain looking flower in visible light has markings seen with UV that guide the bees to the flower's nectar. Voles will mark their trails with urine that reflects UV, a small hawk called a kestrel uses this to narrow its hunt for voles.

Ultraviolet penetrates your skin up to 1 cm. The energy of the UV can disrupt molecules in your cells, such as DNA. The body to protect itself from damage manufactures a chemical to absorb the UV light. This chemical produces darker skin pigment. Be aware that exposing yourself to UV causes cell damage, ages the cells quicker and can lead to cancer. Brazil has banned tanning beds. Many countries restrict access by young people to tanning salons. In France, you are allowed to buy cigarettes at a younger age than going to a tanning tomb booth! Both activities lead to cancer.

## EM Spectrum Data Table

Name Wavelength Range Wavelength
(comparative size)
Frequency Range Energy
ionizing/ med / lo
Sources Uses
Ultraviolet

## Waves Glossary

Electromagnetic waves
Radiation consisting of waves of energy sent through space and matter associated with electric and magnetic fields resulting from the acceleration of an electric charge (light, x-rays, microwaves, gamma rays, etc.). 3.9
Frequency
The number of back-and-forth cycles per second, in a wave or wave-like process. 3.5
Period
The time for one wavelength to pass a point. The time for a wave to travel the distance of one wavelength. P= 1/frequency. 3.5
Wave
A rhythmic disturbance that transfers energy from place to place. 3.5
Wavelength
The distance measured from crest to crest of one complete wave or cycle. 3.5