# 0.7 Electromagnetic radiation  (Page 6/6)

 Page 6 / 6

Cellphone users are recommended to minimise their exposure to the radiation, by for example:

2. Keep the mobile phone away from the body.
3. Do not telephone in a car without an external antenna.

## Exercise - penetrating ability of em radiation

1. Indicate the penetrating ability of the different kinds of EM radiation and relate it to energy of the radiation.
2. Describe the dangers of gamma rays, X-rays and the damaging effect of ultra-violet radiation on skin.

## Summary

1. Electromagnetic radiation has both a wave and a particle nature.
2. Electromagnetic waves travel at a speed of $3×{10}^{8}\phantom{\rule{3.33333pt}{0ex}}m·{s}^{-1}$ in a vacuum.
3. The Electromagnetic spectrum consists of the follwing types of radiation: radio waves, microwaves, infrared, visible, ultraviolet, X-rays, gamma-rays.
4. Gamma-rays have the most energy and are the most penetrating, while radio waves have the lowest energy and are the least penetrating.

## Indigenous knowledge systems: animal behaviour

People have believed that animals can predict earthquakes and other natural disasters for centuries. As early as 373 B.C., historians recorded a massive exodus of animals, including rats, snakes and weasels, from the Greek city of Helice days before a quake struck causing massive devastation.

This topic is much debated and there are people that claim different behaviours for different kinds of animals, for example:

• Dogs and cats : are believed by some to howl or bite their owners before natural disasters, they cite factors like a much stronger sense of smell.
• Sharks : have been reported to move to deeper water before hurricanes, possibly because a sensitivity to changes in the air pressure preceding the hurricane.
• Elephants : will allegedly trumpet and flee to higher ground before a tsunami arrived.

Others argue that many animals detect certain natural signals, such as the early tremblings of an earthquake, long before humans. This means they have opportunity to react before we can but argue that they exhibit no special understanding, they just flee as would any person hearing a shout of fire.

Another problem cited with these seemingly clairvoyant animals is that their psychic powers often are based on behaviors that people only recall after the event. Some animal behaviors happen frequently, but are not remembered unless an earthquake, tsunami, or mud slide follows. For example, if you see a dog cross a road, you just remember you saw a dog cross the road. But if an earthquake shook your neighborhood five minutes later, would you say the dog was fleeing?

## Project: indigenous knowledge: animals and natural disasters.

Carry out research on the behavior of animals before natural disasters.

Pick one type of natural disaster (earthquake, flood, tsunami, etc.) and see what you can find about animals reacting to that type of disaster. Ask people you know about what they have heard to get a sense of folklore.

Then research the topic to find more information and remember to critically assess all information. Things to consider:

• What scientific research has been conducted?
• Which countries does that type of disaster usually occur in?
• Do any of the native people of that country have legends/ideas about animals reacting to the disaster?
• What do people believe leads to this behavior? i.e. do the animals have some mystic ability or are they more sensitive to anything then we are (such as low frequency radiation)

Present your findings to your class. Critically analyze all the information you collect and decide what you believe.

## End of chapter exercise

1. What is the energy of a photon of EM radiation with a frequency of $3×{10}^{8}$  Hz?
2. What is the energy of a photon of light with a wavelength of 660 nm?
3. List the main types of electromagnetic radiation in order of increasing wavelength.
4. List the main uses of:
2. infrared
3. gamma rays
4. X-rays
5. Explain why we need to protect ourselves from ultraviolet radiation from the Sun.
7. What precautions should we take when using cell phones?
8. Write a short essay on a type of electromagnetic waves. You should look at uses, advantages and disadvantages of your chosen radiation.
9. Explain why some types of electromagnetic radiation are more penetrating than others.

what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
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Rafiq
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Mahi
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Rafiq
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
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