M. Manser (2014)

Module P1:  EM waves  UV, skin cancer and sunburn  CFCs and the ozone layer M. Manser Sackville School

Name, in order of frequency or wavelength, the seven parts of the electromagnetic spectrum. Explain the effect of skin pigment on the risk of cancer Calculate how long a person may safely spend in the sun using SPF Describe how the ozone layer protects the Earth from ultraviolet radiation and the damaging effect of CFCs

M. Manser Sackville Schooll

The shorter the wavelength (and higher the frequency) of electromagnetic waves, the more energy that they carry. gamma rays X-raysUV visible light infraredmicrowaves radio waves energy increases hazard increases High-frequency electromagnetic waves, such as gamma rays, are potentially more harmful because they have more energy nm100 nm1 nm0.01 mm1 mm10 cm10 m

absorption – The process in which electromagnetic waves hit a surface and their energy is transferred to the material. electromagnetic spectrum – The continuous series of electromagnetic waves in order of wavelength or frequency. frequency – The number of waves passing a point every second, measured in hertz (Hz). gamma rays – Electromagnetic waves with the shortest wavelengths. Uses include sterilizing medical equipment and cancer treatment. infrared waves – Electromagnetic waves given off by hot objects. Uses include heating, cooking and remote controls. microwaves – Electromagnetic waves that are short- wavelength radio waves. Uses include mobile phones, radar and cooking.

radio waves – Electromagnetic waves with the longest wavelengths. Used for communications. reflection – The process in which electromagnetic waves bounce back from a surface. wavelength – The distance between two matching points on neighbouring waves, which is measured in metres. ultraviolet rays – Electromagnetic waves that can be absorbed by certain chemicals and emitted as visible light. Uses include tanning beds and security marking. visible light – Electromagnetic waves that are detected by our eyes, allowing us to see. Other uses include optical fibre communications and imaging. X-rays – Electromagnetic waves that pass through most materials. Uses include medical imaging and security.

Ultraviolet rays and the ozone layer Ozone Ozone, O 3, is a form of oxygen that is different to O 2. Ozone is formed from oxygen in a reversible reaction.

Ultraviolet rays and the ozone layer The ozone layer The ozone layer is the part of the upper atmosphere where ozone is found in the highest concentrations. The ozone there absorbs ultraviolet radiation, preventing most of it from reaching the ground. This is important because ultraviolet radiation can lead to skin cancer.

Ultraviolet rays and the ozone layer CFCs were once used widely in insulating foam and aerosol spray- cans. Once released, they gradually spread through the atmosphere, eventually reaching the ozone layer. Once there, they destroy ozone. CFCs have now been almost completely replaced by chemicals that do not cause this damage. The ozone layer Near the end of the last century, scientists discovered that ozone levels over the Antarctic were reduced. This discovery was unexpected. Chemists knew that reactive chlorine atoms could destroy ozone. They also knew that chemicals called chlorofluorocarbons - CFCs - break down in ultraviolet light to release reactive chlorine atoms. Scientists used these ideas to explain the low ozone levels.

Exposure to ultraviolet radiation

Everyday we are exposed to ultraviolet (UV) radiation emitted by the Sun. ultra- violet infrared X-rays gamma rays wavelength of electromagnetic waves The wavelength of UV radiation ranges from 10 to 1000 nm. that bees, birds, butterflies and other insects can. UV radiation is high-energy electromagnetic radiation that is found between visible light and X-rays on the electromagnetic spectrum. Humans cannot see UV radiation but research has shown

Ultraviolet radiation is emitted by very hot objects, such as the Sun. Some gases emit ultraviolet radiation when an electric current is passed through them. Electrical sparks and arc welding also reach temperatures that are high enough to produce ultraviolet radiation. Tanning beds and the ‘black lights’ seen in night clubs use ultraviolet rays that have been produced in this way.

Bright clothing Certain chemicals can absorb UV radiation and then re-emit it as visible light. Some washing powders use these to make white material appear whiter in sunlight. Such chemicals are also used in safety clothing. Tanning UV radiation in sunlight causes skin to tan. Tanning beds imitate sunlight by emitting artificially-produced UV rays. Security marking Special inks, that are only visible under UV radiation, are used to security mark expensive items.

Chemicals that absorb energetic ultraviolet radiation and re-emit it as less energetic visible light are said to be fluorescent. These chemicals are used in inks and in safety clothing. Fluorescent inks, that are not visible under normal light, are used in banknote production to prevent fraud. The inks identify genuine banknotes by glowing brightly under ultraviolet light. Fluorescent inks are also used in stamps to distinguish different values for automatic sorting.

The skin uses UV radiation from the Sun to make vitamin D, which is needed for strong bones. Some exposure to UV radiation is beneficial but overexposure is generally harmful to the skin and eyes. Ultraviolet radiation can damage cells. Sunburn occurs when the skin is exposed to high-intensity ultraviolet radiation, which damages and kills skin cells. Intense UV radiation can inflame the eyes and long-term exposure may cause cataracts. Over time, repeated exposure leads to premature ageing of the skin and increases the risk of skin cancer.

Some people think that a suntan is safe and makes them look healthy. Not all skin types are able to tan. This is why fair skin and skin that is easily sunburnt is most at risk from UV damage. In fact, a suntan is a sign of skin that has been damaged by UV radiation. It is the skin’s attempt to protect cells from further damage by creating its own sunscreen. The pigment MELANIN is produced which then protects the layers below. A suntan only provides some protection and naturally dark or tanned skin can still suffer sunburn. People with dark skin naturally have more MELANIN pigment in their skin. Everyone, regardless of skin type, is at risk from eye damage caused by UV radiation.

Prolonged exposure to UV radiation carries serious health risks and so protection is important. A combination of measures can protect skin and eyes from UV radiation: Cover up, stay in the shade, wear a wide- brimmed hat and sunglasses. Sunblock and sunscreen protect the skin by blocking UV radiation. When out in the Sun for prolonged periods, these should be applied to the skin generously and often. Time you can safely = SPF x the time it normally stay in the sun takes for your skin to burn