Spectra
● Dispersion of light
○ The phenomenon of splitting up of a white light into its constituent colours
○ E.g. rainbow
● The cause of dispersion of light is that white light consists of 7 different colours
● Electromagnetic waves can all be reflected, refracted and diffracted
● Wavelength decreases ------->
● Frequency increases --------->
● Energy increases -------->
Uses of electromagnetic waves
● Radio waves
○ Detected by aerials
○ Used for communication (broadcast radio and television signals)
● Microwaves
○ Detected by aerials (diodes)
○ Communication (satellite television broadcasting)
○ Cooking
○ Used to transmit mobile phone signals between masts
● Infrared
○ Emitted by hot objects
○ Detected by skin/ thermometer/ photographic film
○ Used for seeing
● Ultraviolet radiation
○ Emitted by hot objects
○ Detected by skin, photographic film
○ Used for sun tanning
○ Energy efficient lamps
○ Phototherapy
○ Killing bacteria (water disinfection)
○ Creating fluorescent effects
○ Equipment disinfection (food, beverage, air)
● Gamma ray
○ Emitted by nuclei
○ Detected by photographic film, geiger-muller tubes
○ Used for treating cancer
○ Detecting faults in metals and concrete
○ Sterilising equipment or killing bacteria in food
○ Can damage or mutate human cells, which can lead to cancer
● X-ray
○ Emitted by atoms
○ Detected by photographic film
○ Used for x-ray photographs in medicine
○ Detecting faults in metals and concrete
○ Can damage human cells
● Electromagnetic hazards
○ Overexposure to certain types of electromagnetic radiation can be harmful
○ Higher the frequency of the radiation, the more damage it is likely to cause to the body
● Microwaves can cause internal heating of body tissues
● Infrared radiation is felt as heat and cause skin to burn
● X-rays damage cells causing mutation and cell death. May lead to cancer
● Gamma rays also damage cells causing mutation and cell death
