Science Practical Shots - See To Yu Xiang and Christopher John

Above: First event

Reflection:

Q1.

Q2.

Level Test for Science on 28 July 2011 (Thursday)

Topics to be tested:
General wave properties
Electromagnetic Spectrum
Reflection

Duration: 1h

Test Structure:
MCQ - 10 marks
Short Structure Question - 25 marks
Long Question - 10 marks
Total: 45 marks

Things to bring:
Writing materials including pencil
Calculator
Protractor
Ruler

Visible Light

Visible light waves are the only electromagnetic waves we can see. We see these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light. 

Visible spectrum (in order from the shortest wavelength to the longest)
 
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet
 





Advantages:
- Allows us to see.
- Are readily absorbed or reflected, giving us color

Disadvantages:
- Wavelengths are too long to permeate skin, hence the use of shorter X-rays instead to examine bone structure of a living being.

- Are readily absorbed/reflected, which is why we discern the colors of objects; this is not a good thing for transmitting information over long distances, hence the use of much longer wave length radio waves

- Not easily discernible at low levels (i.e., in the dark). Switching to the slightly longer infrared allows tracking of heat sources such as machinery and living things in the dark.

Q1) Why of all colours, only blue is reflected off the sky and the sea?

The blue sky colour is due to Rayleigh scattering (It refers to the scattering of light off of the molecules of the air, and can be extended to scattering from particles up to about a tenth of the wavelength of the light). As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.

However, much of the shorter wavelength light is absorbed by gas molecules. The absorbed blue light is then radiated in different directions and gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. The sea is coloured due to the same reason.

Q2) Why is the sunset red?

As the sun begins to set, the light must travel farther through the atmosphere before it reaches you. More of the light is reflected and scattered. As less reaches you directly, the sun appears less bright.

The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes. 

Q3) How do we see colour?
What we actually see as color is known as its colour effect. When an object is hit with light rays, the object absorbs certain waves and reflects others, this determines the color effect. For example, when we observe a red fluorescent lamp, it appears red because it reflects only red light and absorbs all other light.

The lamp does not have color in itself. The light generates the color. What we see as color is the reflection of specific wavelength of light rays off an object.

The color white: If all light waves are reflected from a surface the surface will appear to be white.
The color black: Similarly, when all light waves are absorbed by a surface the surface will appear to be black.

Sources: google.com

X-ray: Yu Chong, Davina, Jia Le, Jun Hong

>

Questions	Answers
What is X-ray?	- A form of electromagnetic radiation. Wavelength: 0.01-10 nanometers Frequency: 3×1016 Hz to 3×1019 Hz Energy: 120 eV to 120 keV. Soft X-ray: about 0.12 to 12 keV (10 to 0.10 nm wavelength) Hard X-ray: about 12 to 120 keV (0.10 to 0.01 nm wavelength)
What is some usages of it?	Another use of radiography is in the examination and analysis of paintings, where studies can reveal such details as the age of a painting and underlying brushstroke techniques that help to identify or verify the artist. X rays are used in several techniques that can provide enlarged images of the structure of opaque objects. These techniques, collectively referred to as X-ray microscopy or microradiography, can also be used in the quantitative analysis of many materials. It is also used in X-ray therapy to destroy diseased cells.
What is one danger of it?	Can cause mutations One of the dangers in the use of X rays is that they can destroy living tissue and can cause severe skin burns on human flesh exposed for too long a time.
How many times can someone be exposed to X-ray?	Less than 36 times per year - The radiation is equivalent to over 10 days of normal light radiation
Safety of doctors and attendants in the hospital	Depending on the peak voltage, the thickness of lead that is needed to be worn differs
Created by	X-ray fluorescence: If the electron has enough energy it can knock an orbital electron out of the inner electron shell of a metal atom, and as a result electrons from higher energy levels then fill up the vacancy and X-ray photons are emitted. This process produces an emission spectrum of X-rays at a few discrete frequencies, sometimes referred to as the spectral lines. The spectral lines generated depend on the target (anode) element used and thus are called characteristic lines. Usually these are transitions from upper shells into K shell (called K lines), into L shell (called L lines) and so on. Bremsstrahlung: This is radiation given off by the electrons as they are scattered by the strong electric field near the high-Z (proton-number) nuclei. These X-rays have a continuous spectrum. The intensity of the X-rays increases linearly with decreasing frequency, from zero at the energy of th e incident electrons, the voltage on the X-ray tube.
What is the instrument used to create X-ray?	X-rays can be generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. The high velocity electrons collide with a metal target, the anode, creating the X-rays. In medical X-ray tubes the target is usually tungsten or a more crack-resistant alloy of rhenium (5%) and tungsten (95%), but sometimes molybdenum for more specialized applications, such as when soft X-rays are needed as in mammography. In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem.

wikipedia.com

Ultraviolet Light: by Jonan, Min Suk and Yu Xiang

What is Ultraviolet light?
Ultraviolet light is the wavelength of the electromagnetic spectrum where:
- Wavelengths range from 400nm to 10nm
- Energy per photon is 3-124 eV (where 1eV is equivalent to 1.602×10^−19 J)
Ultraviolet light has a wavelength beyond the color violet, which is why its called ultra(beyond)violet.

Discovery
UV radiation was discovered by:
- Johann Wilhelm Ritter in 1801
- Victor Schumann is 1893 (who discovered UV rays with wavelengths below 200nm)

Properties
UV light is capable of:
- causing fluorescence in otherwise non-luminescent objects
- causing damage to DNA
- ionizing gas
UV light is also released by astronomical objects and it can be seen by some animals.

These main capabilities of UV light therefore make it useful in a number of...

Applications
...where UV light is used to:
- prevent counterfeiting through the inclusion of fluorescent materials into debit cards and banknotes
- analyse crime scenes (body fluids like saliva and semen fluoresce)
- operate fluorescent lamps by causing the mercury vapor within to fluoresce
- view astronomical objects (like the Sun)
- identify animals that fluoresce under UV light
- control pests by tracking urine trails
- purify air and water through UV irradiation

Other application for UV light by wavelength are: (list sourced from Wikipedia. url:http://en.wikipedia.org/wiki/Ultraviolet#Applications_of_UV

13.5 nm: Extreme Ultraviolet Lithography
230-400 nm: Optical sensors, various instrumentation
230-365 nm: UV-ID, label tracking, barcodes
240-280 nm: Disinfection, decontamination of surfaces and water (DNA absorption has a peak at 260 nm)
250-300 nm: Forensic analysis, drug detection
270-300 nm: Protein analysis, DNA sequencing, drug discovery
280-400 nm: Medical imaging of cells
300-400 nm: Solid-state lighting
300-365 nm: Curing of polymers and printer inks
300-320 nm: Light therapy in medicine
350-370 nm: Bug zappers (flies are most attracted to light at 365 nm)

Types of UV light
Like visible light, UV light has multiple distinct wavelengths possessing unique properties. There are 3 main types of UV light:
- Ultraviolet A, long wave UV or black light, λ of 400-315 nm
- Ultraviolet B, medium wave UV, λ of 315-280 nm
- Ultraviolet C, short wave UV, germicidal UV, λ of 280-100nm
UV light with wavelengths ranging from 200-10nm are strongly absorbed by oxygen in the air. Oxygen is opaque at those wavelengths.

Sources
UV light is produced through natural and artificial means like:
- The Sun (which produces UVA, UVB and UVC)
- Black lights (producing mainly UVA and some visible light)
- Ultraviolet lasers (producing high UVA to low UVC)

Hazards
UV light is as dangerous as it is beneficial. UV light is partially responsible for:
- Skin cancer
- Skin aging
- Sunburn (which can happen for both your skin and your EYES (where it is called arc eye))

Sources:
http://en.wikipedia.org/wiki/Ultraviolet
http://science.hq.nasa.gov/kids/imagers/ems/uv.html
http://www.nas.nasa.gov/About/Education/Ozone/radiation.html

Microwaves

Interesting videos on Microwaves:

Ostrich egg in microwave over (Brainiac)

http://www.youtube.com/watch?v=IMM7s5RRqT4

Cell Phones cook popcorn

http://www.youtube.com/watch?v=lg_dyD0Nsjw

*Note:

Settings

Eggs explode when put into the microwave due to the fact that the yolk’s sack is virtually indestructible. Thus, when heat is applied, the yolk expands till it reaches it’s maximum pre

ssure point and it will then burst.

Microwaves:

Microwaves can be useful in many ways. Some of the most outstanding ways where microwaves are used is for communication (phone), radar, radio astronomy, navigation and for cooking.

Microwave Ovens :

A microwave oven uses microwaves to heat food. Microwaves are electromagnetic waves. In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz). The waves in this frequency are absorbed by water, fats and sugars. When they are absorbed they are converted directly into atomic motion, heat. They are not absorbed by most plastics, glass or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven.

Dangers:

Prolonged exposure to microwaves is known to cause harmful effects to the body. Cataract (clouding of eye lens) is common due to the radiation from the microwaves. Recent research indicates that microwaves from mobile phones can affect parts of your brain and you would be more vulnerable if you're young and your brain is still growing.
So the advice is to keep calls short and never stand close to the microwave oven when it’s turned on.

Sources:

http://www.darvill.clara.net/emag/emagmicro.htm

http://home.howstuffworks.com/microwave1.htm

8:55 AM

http://home.howstuffworks.com/microwave2.htm

Done By : Johanan Teo, Hardy Shien, Chan Jun Wei

Infrared Radiation

Advantages:

• Infrared is the radiation important by the Earth's weather and climate.

(if not there would be global warming or global cooling)

• Low power and cost requirements (to power electronic devices) 
• Allows images to be produced at night (Night vision)
• Are used to ionize gases which later are used for helpful purposes
• Allows people to do Medical treatments

Greenhouse effect:

Greenhouse gases in the atmosphere, especially water vapor, absorb and emit some of this infrared radiation, and keep the earth habitably warm. Clouds also produce their own greenhouse effect. 

Water vapor (H2O) is the most active molecule in absorbing infrared radiation and thus in heating the atmosphere. It accounts for about 55% of the absorption of thermal radiation in the atmosphere.

Carbon dioxide (CO2) also absorbs infrared radiation and accounts for about 18%, methane (CH4) accounts for about 6% and ozone (O3) accounts for about 5% of heating the atmosphere.

Since some infrared radiation is lost into space, the recent percentages of carbon dioxide and methane in the atmosphere have allowed the temperature to remain stable.

CO2 has stayed at the proper percentage in the atmosphere until recently, when an increasing amount of the gas has been emitted due to the burning of fossil fuels. Automobile exhaust and industrial smoke contribute the most CO2.

The reason why the air cools so quickly on a clear, dry evening is because the lack of humidity and clouds allows large amounts of IR radiation to escape rapidly to outer space as it is emitted upward by the ground and other surfaces.

Disadvantages:

Line of sight: transmitters and receivers must be almost directly aligned (i.e. able to see each other) to communicate 

Blocked by common materials: people, walls, plants, etc. can block transmission 

Short range: performance drops off with longer distances 

Light, weather sensitive: direct sunlight, rain, fog, dust, pollution can affect transmission 

Speed: data rate transmission is lower than typical wired transmission

Bad effects of infrared:

Gradual Opacity of the Eye's Lens

Uses:

 We cannot see infrared radiation, but we can feel it as heat energy. Infrared sensors can detect heat from the body. They are used in:

• security lights
• burglar alarms

Infrared radiation is also used to transmit information from place to place, including:

• remote controls for television sets and DVD player
• data links over short distances between computers or mobile phones
• Photographers use film that is sensitive to infrared rays to take pictures in places where there is no visible light. Burglar alarms also use infrared.

Done by: Cherin, Benjamin, Si Yuan and Niklaus

Gamma Radiation - Rayner, Preston, Christopher

Gamma Rays have the highest frequency in the electromagnetic spectrum. There are many uses for it like radiation treatment, sterilizing, etc. But they are also very dangerous. They can cause radiation sickness and eventually, death after long term exposure.
A short video about Gamma Radiation: http://www.youtube.com/watch?v=okyynBaSOtA
A short video about Alpha, Beta and Gamma Radiation: http://www.youtube.com/watch?v=TSiNXBLfzK4


Source:
- Neutron stars
- Cobalt 60
- Decay of high energy states in atomic nuclei & high energy sub-atomic particle interactions in natural processes and man made mechanisms


Uses:
- For radiation therapy. It turns out that though electromagnetic radiation(emr) damage can make living cells "sick" and can also kill them if enough damage occurs, the cells that are most sensitive to emr damage are cells that have "fast metabolisms" or that work at high rates. Cancer cells work at high rates. Irradiate them with high energy emr (gamma rays) and they can be killed. So will some surrounding tissue, but the brunt of the damage will be caused to the cancerous tissue. And by moving the beam around, we can minimize damage to surrounding tissue while pounding the cancerous cells. This is the basis for currentradiation therapy by gamma rays.
- Sterilization of surgical equipments to remove viruses and micro-organisms.
- Gamma-induced molecular changes can also be used to alter the properties of semi-precious stones, and is often used to change white topaz into blue topaz.
- Gamma rays are also used for diagnostic purposes in nuclear medicine in imaging techniques. A number of different gamma-emitting radioisotopes are used. For example, in a PET scan a radiolabled sugar called fludeoxyglucose emits positrons that are converted to pairs of gamma rays that localize cancer (which often takes up more sugar than other surrounding tissues). The most common gamma emitter used in medical applications is the nuclear isomer technetium-99m which emits gamma rays in the same energy range as diagnostic X-rays. When this radionuclide tracer is administered to a patient, a gamma camera can be used to form an image of the radioisotope's distribution by detecting the gamma radiation emitted (see also SPECT). Depending on what molecule has been labeled with the tracer, such techniques can be employed to diagnose a wide range of conditions (for example, the spread of cancer to the bones in a bone scan).


Risks:
- Gamma radiation can break and split DNA molecules
- They are absorbed or scattered by anything they pass through, and their ability to penetrate material and the amount of scattering they experience varies as the material. But they penetrate stuff pretty well, and slice right through biological stuff like plant or animal tissue. And they do stuff to the tissue they pass through while zipping past.

The high energy of gamma rays is what is called ionizing radiation. It has the power to break chemical bonds between atoms. This is important because living tissue is made up of complex chains of atoms. Big organic molecules are the basics of life. If a gamma ray zips by, it can break the big molecule apart kind of like snipping a string in a place or two with scissors. The gamma ray loses energy doing this, but it still continues on cutting up molecules. It causes radiation damage. Electromagnetic radiation (emr) damage. And this can be good.


Summary:
- Gamma radiation has the highest frequency in the electromagnetic spectrum.
- Its source is the decay of high energy states in atomic nuclei & high energy sub-atomic particle interactions in natural processes and man made mechanisms, neutron stars, Cobalt 60
- Uses are: To eradicate cancer cells, alter properties of semi-precious stones, sterilization of equipments, diagnostic purposes in nuclear medicine in imaging techniques.
- Risks: It can kill you and split your DNA

Radio waves

What are radiowaves?
Radio waves do more than just bring music to your radio. They also carry signals for your television and cellular phones. Cellular phones use radio waves to transmit information. These waves are much smaller that TV and FM radio waves.

What are the dangers of too much radio waves?
Large doses of radio waves are believed to cause cancer, leukemia and other disorders. Some people undeniably experience pain and other symptoms that those people attribute to their hypersensitivity to radio signals, but said there is no proof that radio signals are indeed the cause of the pain.

What is the difference between FM and AM on radios?
M stands for “frequency modulation” and AM stands for “amplitude modulation".
AM radio ranges from 535 to 1705kHz (kilohertz, or thousands of cycles per-second of electromagnetic energy). These are the numbers you see on your AM radio dial.

How far an AM station's signal travels depends on

1. The station's frequency (channel)
   
2. The power of the transmitter in watts
   
3. The nature of the transmitting antenna
   
4. How conductive the soil is around the antenna (damp soil is good; sand and rocks aren't)
5. Ionospheric refraction. (The ionosphere is a layer of heavily charged ion molecules above the earth's atmosphere.)

The FM radio band goes from 88 to 108 MHz (megahertz, or millions of cycles per second). Again, you can see these numbers on your FM radio dial.

To keep from interfering with each other, FM stations must be 200kHz apart within the same geographic area. However, since the signals of FM stations cover only limited distances, the same frequencies can be used in different geographic areas of the country.
First, these waves go in a straight line and don't bend around the earth as AM ground waves do. Thus, they can quickly disappear into space so the farther away from the FM or TV station you are, the higher you have to have an antenna to receive the FM or TV signal.
There's another problem: Since FM and TV signals are line-of-sight, they can be stopped or reflected by things like mountains and buildings. In the case of solid objects like buildings, reflections create ghost images in TV pictures and that "swishing sound" when you listen to FM radio while driving around tall structures.
Of course, the higher the FM or TV transmitter antennas are the greater area they will cover and this explains why these antennas are commonly very tall, or placed on the top of mountains. AM radio doesn't need that kind of advantage, since AM radio waves don't behave in the same way.

References:
http://news.techworld.com/green-it/3204279/radio-waves-may-be-dangerous-says-french-government/
http://science.hq.nasa.gov/kids/imagers/ems/radio.html
http://www.darvill.clara.net/emag/emagradio.htm
http://www.cybercollege.com/frtv/frtv017.htm
http://www.mentalfloss.com/difference/fm-vs-am/

Done by Michelle Dapito & Naveena Menon

Worksheet 1 Example 3

a) Speed = 90cm/1.69seconds ≈ 53.3cm/s (3s.f.)

Ans: 53.3cm/s

b) No it is not possible. Adjusting either the amplitude or the damping does not affect the speed of the wave pulse. But, adjusting the tension would change the speed and the wavelength.

(The below pictures are some factors that we changed, but only changing the tension will change the speed.)

Done By: Benjamin Fheng and Lee Si Yuan :D

Worksheet 1 Example 3

a) Wavelength = 16cm

 Aprox. 5.5 wavelengths in 90cm 

5.5 ÷ 90 = 0.307 (Fre

0.16 (Wavelength) ÷ 0.307 (Period) =  0.52m/s

b) Only tension will affect the speed. The rest of the factors (ie. amplitude, damping)  WILL not 

affect

Set up with damping adjusted

Set up with tension adjusted

Set up with amplitude



Done by: Cherin and Yu Xiang

General Properties of Waves (Worksheet 1, Example 3)

a) Wavelength in METRES = 30cm = 0.3m
Period in SECONDS = 0.66 s
Speed of the wave pulse = 0.3/0.66 = 0.455 (to 3 significant figures)

b) It Is possible to change the speed of the wave length without changing the width. If you change the amplitude by increasing or decreasing it, either way the speed and of the wave pulse and length will not be affected. Thus this have no effect, but if you half the tension, the wavelength will be divided by 3 and the speed will decrease by 5.5 times. To allow the pulse length to be 30cm, you can set the tension at about ¾ and the pulse length to be 100 cm. This will achieve the same width of 30 cm but at a slower pace, about 4 times slower. Thus we can conclude that changing tension lower and increasing the pulse length can reduce the speed of the wavelength. So if you increase the tension and decrease the pulse length, it should be possible to achieve a faster speed of the wave pulse. Thus this fulfills the condition of having the same width of pulse length while just changing the speed. Thus it should be possible.






Done by Michelle Dapito & Niklaus Teo.

General Properties of Waves (Worksheet 1, Example 3)

a)
Wavelength= 16cm= 0.16m
Time= 1.44s
Velosity= 16/1.44= 0.111m/s (3sf)
Ans: 0.111m/s (3sf)

b)
It is not possible to change the speed of the wave pulse without changing the width. Regardless of the amplitude and damping, the wavelength would still be 16cm.

Done by: Gwendolyn

General Properties of Waves (Worksheet 1, Example 3)

(a) Velocity = 30/1.69
                = 17 127/169 cm/s
Ans: 17 127/169 cm/s
(b) No, it is not possible. Adjusting either the amplitude or the damping does not affect the speed of the wave pulse. However, adjusting the tension would change the speed, but it would also change the width of the wave pulse.

Control experiment

Damping adjusted

Amplitude adjusted

Tension adjusted

Done By: Stacey and Naveena

Worksheet 1 General Properties of Waves Example 3

a)

T = 30s

T = 1/f

30 = 1/f

30f = 1

f = 1/30Hz

入 = 16cm = 0.16m

v = 入 x f

v = 0.16 x 1/30 = 2/375 = 0.00533(to 3 sig. figures)

b)

No, its is not possible. Even if the amplitude, which is the maximum height of the wave from the rest point, is changed, the wave will always travel 0.57m in 60s unless the amplitude is 0, which means there is no wave. The screenshots below proofs it.

This means that the waves are moving at the same speed each time because they reach the same point in the same time everytime.

Done by: Choi Min Suk

Worksheet 1 general Properties of Waves - Example 3

a)
S = 90/1.69

   ≈ 53.3cm/s 3s.f.
Ans: 53.3cm/s

b)

No it is not possible. The below pictures show that the position of the wave is the same for the same amount of time taken. For every 1 second, the furthest end of the wave will always travel 0.58m

Done by: Preston, Christopher, Rayner

Story of Stuff, Full Version; How Things Work, About Stuff

http://www.youtube.com/watch?v=gLBE5QAYXp8

Description: This is a video on the environment/recycling. NOTE: It is 21:16 minutes long

- Benjamin Fheng

Leaf Structures & Functions (with online quiz)

1. http://www.enchantedlearning.com/subjects/plants/leaf/ (Online Readings)

2. http://bioactive.mrkirkscience.com/32/ch32intro.html (Quiz)

3. http://www.biotopics.co.uk/plants/leafst.html (Quiz)

4. http://nhscience.lonestar.edu/biol/biolab/leaf.htm (Quiz)