Electromagnetic Waves, Physics

Most of our daily appliances we use everyday use electromagnetic waves. Electromagnetic waves, such as light, belong to the electromagnetic spectrum.

Gamma rays have the smallest wavelength and highest frequency while radio waves have the longest wave length and lowest frequency.

Electromagnetic waves have been part of our lives, though we cannot see them. They are very useful in many ways.


From this diagram, we can see that electromagnetic waves are transverse waves. In addition, they are both electric and magnetic fields, oscillating at 90° to each other!!

They can transfer energy from one place to another. For example, electromagnetic waves from the Sun transport thermal and light energy through space to the Earth. To add on, electromagnetic waves are able to travel through vacuum and do not require any medium to travel from one point to another.

These electromagnetic waves obey laws of reflection and refraction. They also do no carry any electrical charge as they are neither positively nor negatively charged.

Apart from that, all their frequencies do not change when they travel from one medium to another. This is because their frequency depend only on their source.


Gamma Rays are used for radiation therapy, or in other words, to treat cancer. These rays are directed at cancerous tumors to kill cancer cells.

X-rays are used for medical purposes too. They can penetrate any material as therefore can also be used in airports for security checks.

Ultraviolet radiation is used in sterilisation of medical equipment and artificial tanning.

Visible light is used everywhere!!!

Infrared is also another ray being used almost everywhere! Our remote controllers, ear thermometers etc. all use electromagnetic waves

Microwaves are used in satellite tv's, penetrating thorough smoke, haze, light rain and clouds. However, these rays must be directed properly, from one satellite dish to another without any obstruction.

Radio waves are not only used radio but also wireless telegraphy, radar, navigation, telephone transmission etc.Unlike microwaves, they are able to go able objects due to their longer wavelength.

Grammar Blitz: Using the Passive

Passive tone of writing is used to focus on the action itself, or the object affected by the action, rather than the 'subject' or the 'doer' of the action.



For instance:

The student threw the book - Active
The book was thrown by the student - Passive



The newspaper revealed the truth - Active
The truth was revealed by the newspaper - Passive



More examples:

Water covers the greatest parts of the Earth's surface - Passive
The greatest parts of the Earth's surface is covered by water - Active



The major impact made by human beings on living marine resources has occured in the last 100 years - Passive
Human beings made a major impact ... ... - Active



Ships in the open sea discharge oil with impunity - Active
Oil with impunity was discharged by ships in the open sea - Passive



The helicopter pilots had located the whale - Active
The whale was located by the helicopter pilots - Passive



The fight for survival is a drama played out everyday - Passive
The drama played out everyday is a fight for survival - Active


All creatures, human and animal alike, face the same adversary - Active
The same adversary is faced by all creatures, human and animals alike - Passive

We often lost sight of our objective as we plunged up and down the sand hills - Active
Our obective was often lost sight of ... ... - Passive



Trees must surely indicate the presence of water - Active
The presence of water is indicated by the trees - Passive



Modern inventions have speeded up people's lives amazingly - Active
People's live have speed up amazing by modern inventions - Passive

Mobile phones enable us to log on to news, even from mountain top - Passive
We are able to log on to news through mobile phones, even from mountain top - Active

Summary Practice - A tragic turn of events

A Tragic Turn of Events

Summary of Article from 'Today' 07 Apr 2009

A food poisioning outbreak at Geylang Serai market last week was a tragic to those who lost their families and loved ones.

Canteen operator Mdm Aminah Samijo with no medical problems, fell into a coma after consuming the rojak. She died yesterday at Changi General Hospital due to acute renal failure.

Following this incident, 38-year old Mdm Rosiah suffered a miscarriage of her unborn two-month old baby. Another expectant mother, Mdm Sarina also fell ill after eating the rojak. Doctors said that miscarriages due to food poisioning are rare, unless caused by serious strain of bacteria. It is advisable for expectant women to eat cooked food and pay attention to how food is handled.

Altogether, there are 111 cases of similar food poisoning from hospitals such as Alexandra hospital and KK Women's and Children Hospital. The Ministry of Health directed stallholder and assistant of Indian rojak stall 320, also known as Rojak Geylang Serai, to undergo screening at the Communicable Diseases Centre.

Personal thoughts:

After learning this tragic event, I feel that we should pay even more attention on how to handle food, especially raw food!

Words of the Week posted on 12 Apr 09

New Words

1. Beguiling - A beguiling person or thing seems attractive and interesting, but may be dangerous.

2. Apprehensive
Mrs Tan is apprehensive about letting her only daughter go overseas on her own.

3. Ambiguity - Something that is not clear because it has more than one possible meaning.

4. Abhorrence - The feeling that you have when something offends you a lot or you think it is immoral.

5. Acquaintance
He recognized Mr Hunter as an old business acquaintance from his years in banking.

6. Bewilder
He was bewildered by the many decisions he had to make as the team leader.

7. Self-conscious
Lily was self-conscious about her weight.

8. Melodious - Beautiful to listen to.

Waves , Physics

Waves is made of periodic motion, which is a motion repeated at regular motion.The source of any wave is a vibration or oscillation. Waves transfer energy through a medium. Kinetic energy is transferred by waves but the medium is not transferred.

There are two types of waves: transverse and longitudinal waves.

Transverse waves move up and down and the wave motion is perpendicular to the direction of vibration.

Longitudinal waves are a bit different. Waves push and pull, compress and expand.The wave motion is parallel to the direction of vibration.



There are some terms that can describe a transverse wave. There are crest, troughs, phase, wavelength and amplitude. They are depicted in the diagram below.

Crest, Troughs: The highest and lowest point of a transverse wave, respectively.
Phase: Any two points are to be in phase when they move in the same direction and have the same speed and displacement from rest position.
Wavelength(λ): The shortest distance between any two points in a wave that are in phase, such as two successive crest or troughs.
Amplitude: The maximum displacement from rest or center position. It is the height of a crest or depth of a trough measured from the rest position.

Frequency = 1 / T where T = period
Wave speed(v) = λ / T where λ = wavelength

Waves, like light, can reflect and refract. In the refraction of waves, a difference in the depth of water causes a change in speed of waves. The wavelength as well as the speed will increase or decrease but the frequency will remain the same.


The reflection of waves is similar to light. Incoming incident waves are reflected by a barrier and are reflected away.




Sources:

'Discover Physics for GCE'O' Level Science' (2007) ~ Marshall Cavendish Education
http://passmyexams.co.uk/
http://www.physics.ubc.ca/
http://www.science-class.net/Notes/Images_8th_Notes/Transverse-Wave.png
http://www.school-for-champions.com/
http://www.gcsescience.com/