Analysing Electromagnetic Waves

Analysing Electromagnetic Waves

1. The electromagnetic spectrum consists of a group of waves of similar nature. The members of the electromagnetic spectrum arranged in increasing frequencies (decreasing wavelengths) are radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays and gamma rays.
2. Electromagnetic waves are joint electric and magnetic fields which can travel through space with no need of a medium to carry them. Figure shows the representation of electromagnetic waves.
   
3. All the members of the electromagnetic spectrum
   (a) transfer energy from one place to another
   (b) are transverse waves
   (c) can travel through a vacuum
   (d) travel with a speed of 3 x 10⁸ m s^-1 in a vacuum

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The Electromagnetic Spectrum

Table lists out the sources, characteristics and applications of the electromagnetic spectrum.

Type and wavelengths	Sources	Characteristics	Applications
Radio waves λ : 103 — 10-1 m	Radio Television transmitter	Carry audio and visual information	Broadcasting and wireless communication UHF (ultra high frequency) radio waves – TV and mobile phones VHF (very high frequency) radio waves – local radio and wireless communication used by policemen
Microwaves λ : 10-1 – 10-3 m	Radar transmitter Microwave ovens	Can penetrate the atmosphere Suitable for satellite communication Can excite water molecules, therefore suitable for cooking	Communication with satellites Used in radar systems Global Positioning System (GPS) For cooking – microwave ovens
Infrared rays λ : 10-3 – 10-6 m	Warm or hot objects The Sun	Also known as infrared radiation When an object absorbs infrared rays, it becomes hotter	For cooking food – ovens, grills and toasters Remote controls for televisions and video players Intruder alarm systems Night vision
Visible light λ : 8 x 10-7 – 4 x 10-7 m	The Sun Hot objects Electric bulbs Fire LED	Consists of seven components (red, orange, yellow, green, blue, indigo and violet)	Photography Photosynthesis by plants Human and animal sight
Ultraviolet rays λ : 10-7– 10-9 m	The Sun Mercury lamps Sparks Very hot objects	Can be absorbed by glass and the ozone layer in the atmosphere of the Earth A small amount is good for producing vitamin D in our skin while a large amount is bad for eyes and can cause skin cancer	Fluorescent lamp Detection of security markings in currency notes Sterilisation of surgical tools and plant seedlings
X-rays λ : 10-9 – 10-11 m	X-ray tubes Outer space bodies	High energy High penetrating power Very dangerous	Helps doctors to check bones and teeth Helps engineers to check welds and metal joints Kills cancerous cells X-ray diffraction helps scientists to study the arrangement of atoms in various substances To detect whether an art piece is genuine or not
Gamma rays λ : 10-11 m or less	Radioactive substances Cosmic rays	High energy High penetrating power Very dangerous	Kills cancerous cells Sterilisation of surgical tools and food Helps engineers to check welds and metal joints

Detrimental Effects of Electromagnetic Waves

1. The human eye cannot detect ultraviolet rays but an overexposure to these rays can cause blindness. Overexposure to ultraviolet rays can also cause sunburn and skin cancer.
2. Due to the high energy associated with short wavelength radiations, ultraviolet radiations, X-rays and gamma rays can damage living tissues. These radiations ionise atoms and molecules in living cells. These cells may die or become cancerous.
3. X-rays have very high penetrating power. These rays have adverse effects on living cells. Cancer and genetic defects can be induced by exposure to X-rays.
4. Gamma rays have very high penetrating power. Exposure to gamma rays can lead to genetic defects and the harming of living cells.

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