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Abstract
An experiment is described to introduce students in a `hands-on' manner to the physics of instrumentation, measurement, electromagnetic radiation and in particular UV radiation. The students should have no difficulty in setting up the apparatus themselves and they will obtain reliable results within a normal school practical period. Additionally, the students will undertake a scientific experiment relevant to everyday life.
Solar radiation
The sun is the most common form of ultraviolet (UV) radiation to which humans are exposed. The surface temperature of the sun is approximately 5700 oC and at this temperature the peak intensity in the emitted electromagnetic radiation is in the visible waveband along with emission in the infrared and UV wavebands (Parisi & Kimlin, 1997a). A schematic of the wavebands in Figure 1 shows that with decreasing wavelength there is increasing energy per photon of electromagnetic radiation. The UV waveband is subdivided into: UVC - 200 to 280 nm; UVB - 280 to 320 nm; UVA - 320 to 400 nm.
This radiation undergoes scattering and absorption by molecules and aerosols in Earth's atmosphere to form the terrestrial solar UV. The terrestrial UV is comprised of a direct and diffuse component (Parisi & Kimlin, 1998) with no UVC and only part of the UVB present at Earth's surface.
Ultraviolet radiation exposure has a causative role in human skin cancer, eye disorders and premature wrinkling and aging of the skin (Longstreth, de Gruijl, Kripke, Takizawa, & van der Leun, 1995). The effectiveness of UV radiation to produce reddening of human skin or erythema is highly dependent upon the radiation wavelength with some wavelengths more effective than others. The erythemal response of human skin is given by the erythemal action spectrum developed by the CIE (1987) (Figure 2). The y axis is the effectiveness of the wavelengths for producing erythema, normalised to unity for wavelengths of 298 nm and shorter. The most effective UV wavelengths are the UVB and UVC wavelengths. Fortunately no UVC reaches the surface of the Earth. The sensitivity of the erythemal response decreases by a factor of approximately 1000 for the UVA wavelengths. However, there is a higher UVA than UVB irradiance present at Earth's surface.
The media reporting of the predicted UV levels...