Electromagnetic Waves

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Electromagnetic Waves by Mind Map: Electromagnetic Waves

1. transverse waves

2. obey general wave equation

3. travel at a constant speed of 3.0x10^8 m/s

4. does not require medium

5. obey laws of reflection & refraction

6. Radio waves

6.1. lowest frequencies & longest wavelength

6.2. used for radio & TV broadcasting

6.3. also used in remote control cars and walkie-talkie

6.4. reflected by Ionosphere

6.4.1. an electrically charged layer of the upper atmosphere

6.4.2. so they can reach receivers that are not in the line of sight

7. Microwaves

7.1. radio waves with short wavelengths

7.2. used in microwave oven

7.2.1. food is subjected to oscillating electromagnetic fields

7.2.2. causing high polar water molecules to rotate rapidly

7.2.3. heat is generated due to friction/collisions among water molecules

7.2.4. this cannot heat up dry food

7.3. microwave transmission systems use repeaters

7.3.1. a device that receives through one antenna, converts it into an electrical signal and retransmits it

7.3.2. so that large volumes of data can be transmitted over long distances

7.3.3. propagate signals through atmosphere

7.4. also used in mobile phones

8. Infrared (IR)

8.1. NOT heat waves

8.2. sun/light bulbs emits more than half of its radiation in IR

8.3. used in remote controls

8.3.1. one type of remote control signal can only be received by a specific appliance

8.4. used in night vision equipment

8.4.1. they amplify ambient IR and converts it into electric signals, then into visible light

8.5. used in thermal imaging

8.5.1. images are created based on differences in surface temperature

8.5.2. used in airports/public places to detect people with fever during flu epidemics

9. Visible light

9.1. perceived by human eye

9.2. red light at low frequencies, violet light at high frequencies

9.3. continuous spectrum where colour is determined by frequency/wavelength

9.4. used in optical fibres, light photography and endoscopy (visual inspection of internal organs)

10. Ultra-violet rays (UV)

10.1. causes tanning of the skin

10.1.1. because UV stimulates production of a skin pigment (melanin)

10.2. excessive exposure may cause sunburn and even skin cancer from DNA damage

10.3. used by flowers to attract pollinators

10.4. used in bank notes/passports/credit cards

10.4.1. UV watermarks will appear under UV exposure

11. X-rays

11.1. high frequencies & high penetrating capability

11.1.1. so, exposure is hazardous and people have to be well protected

11.1.2. cancer risk from radiation

11.2. used in X-ray medical imaging

11.2.1. boens appear black as most X-ray is absorbed by high density bones

11.2.2. white/grey portions indicate little or no absorption by soft tissues

12. Gamma rays

12.1. highest frequency end of EM spectrum

12.2. most penetrating and highly ionizing form of EM wave

12.3. emitted during radioactive decay of unstable atoms/isotopes

12.3.1. part of the widely known hazardous nuclear radiation

12.4. used to treat cancer patients

12.4.1. rays are targeted at cancerous tumours

12.4.2. but, it can also damage healthy tissues

12.4.3. patients experience nausea, hair loss and haemorrhaging as side effects

12.5. also used to sterilise tools

13. Harmful Effects of Radiation

13.1. only UV rays, X-rays and gamma rays

13.2. ionizing radiation

13.2.1. cause electrons to gain energy

13.2.2. electrons can escape from the atoms

13.2.3. causing atoms to become charged and unstable

13.2.3.1. unstable atoms are more likely to initiate reactions

13.2.3.2. cause mutation in cells due to damaged DNA

13.2.3.2.1. can lead to cancer or faulty generic material being passed down to the offspring