Laboratory Lessons

I find laboratory lessons fun and enriching. We were given a chance to conduct experiments on the topics we had learnt. Like this, it would be much easy to understand it as we would be able to see with our own eyes. I definitely enjoyed the laboratory lessons as we would be able to experience it ourselves without just reading it from a book. At first, I was not able to understand the topic on acid and bases, however, after conducting experiments like 2P06 When Acid Meets Alkali, I am able to see more clearly. When an Acid mixes with an Alkali, salt and water would be formed. We conducted an experiment with dilute hydrochloric acid and dilute sodium hydroxide solution and after the mixture was evaporated to dryness, we observed that a white solid was formed and it was salty in taste. Hence we can conclude that an acid reacts with an alkali to produce a salt. Hydrochloric acid + sodium hydroxide -> sodium chloride + water. I hope that there would be more laboratory lessons in the future.

2011 Term 3 Reflections

I think that this term was quite easy. We learnt about lenses, colours of light and ecology. To me, lenses was quite difficult. We had to remember all the types of images that can be formed with a convex lens, know the properties of it and the uses. It was because we needed to draw the ray diagram. However, after much practice, I am able to understand more. I think that ecology was quite easy. We need to know food chains, adaptations and carbon cycle. It was quite easy to understand and remember. Colours of light was also quite easy. Once I was able to understand the concept and remembering the combinations of the colours, I had no problem doing it. For example, I know that when a red object is placed in yellow light, the object would appear as red because yellow is made up of red and green. Like this, I can use this concept to do on other situations. When a red object is placed in magenta light, it would appear red also as magenta contains red as it is made up of blue and red. I scored quite well for my term test partly because chemistry was not tested. =P I would need to improve on my lenses and revise more on drawing the ray diagrams.

Global Warming

Global Warming

Global warming is the continuing rise in the average temperature of Earth's atmosphere and oceans.The instrumental temperature record shows that the average global surface temperature increased by 0.74 °C (1.33 °F) during the 20th century. They indicate that during the 21st century the global surface temperature is likely to rise a further 1.5 to 1.9 °C (2.7 to 3.4 °F) for their lowest emissions scenario and 3.4 to 6.1 °C (6.1 to 11 °F) for their highest.

Causes

The main cause of Global Warming is the orbital eccentricities of Earth and variations in the Sun’s output. Global Warming occurs in cycles caused mainly by changes in the sun’s energy output, and the sun’s relative position to the earth.

Global warming is also caused by increased concentrations of greenhouse gases in the atmosphere, resulting from human activities such as deforestation and burning of fossil fuels. Industrialization, deforestation, and pollution have greatly increased atmospheric concentrations of water vapor, carbon dioxide, methane, and nitrous oxide, all greenhouse gases that help trap heat near Earth's surface.

Over 95% of the greenhouse effect is the result of water vapor in Earth's atmosphere. But because water droplets held in suspension (clouds) make almost as good a reflector as they do a thermal insulator, there is little rise in daytime temperatures due to the greenhouse effect. Any greenhouse warming, if it does occur, is limited to primarily increasing nighttime temperatures.

Interesting fact: The world's natural wetlands produce more greenhouse gas contributions annually than all human sources combined.

Consequences

An increase in global temperature will cause sea levels to rise. Sea level could rise between 7 and 23 inches (18 to 59 centimeters) by century's end, the IPCC's February 2007 report projects. Rises of just 4 inches (10 centimeters) could flood many South Seas islands and swamp large parts of Southeast Asia. Some hundred million people live within 3 feet (1 meter) of mean sea level, and much of the world's population is concentrated in vulnerable coastal cities. In the U.S., Louisiana and Florida are especially at risk.

Glaciers around the world could melt, causing sea levels to rise while creating water shortages in regions dependent on runoff for fresh water. An increase in global temperature will also change the amount and pattern of precipitation, a probable expansion of subtropical deserts. The growth of deserts may also cause food shortages in many places. A follow-up report by the IPCC released in April 2007 warned that global warming could lead to large-scale food and water shortages and have catastrophic effects on wildlife. More than a million species face extinction from disappearing habitat, changing ecosystems, and acidifying oceans.

Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent occurrence of extreme weather events including heatwaves, droughts and heavy rainfall events, strong hurricanes, species extinctions due to shifting temperature regimes, and changes in agricultural yields.

Reflections:

I feel that global warming has created many problems like the increase in temperature leading to the rise in sea level due to the melting of the glaciers, change the amount and pattern of precipitation and causing more natural disasters like droughts, flood and hurricanes. Thus, we should play a part to stop global warming by controlling our emissions of greenhouse gases. Greenhouse gases traps heat near the Earth’s surface, causing the rise in temperature. We should cut down on our industrialization, deforestation, and pollution as they would greatly increase concentrations of greenhouse gases like carbon dioxide and water vapour. We should start caring for the Earth as early as now as the consequences would be deadly and it would badly affect our future generations and by then, it would be too late to regret and try to make changes as the damages would already be done and it would be very hard to be undone.

Speed of Light

Speed of Light

The speed of light in vacuum is believed to be both universal in nature and constant in time. Its value is 299,792,458 metres per second and it is approximately 186,282 miles per second. It is the maximum speed at which all energy, matter and information in the universe can travel.

History of Speed of Light

In 1667, Galileo Galilei is often credited with being the first scientist to try to determine the speed of light.

His method: Galileo and his assistant each took a shuttered lantern, and they stood on hilltops one mile apart. Galileo flashed his lantern, and the assistant was supposed to open the shutter to his own lantern as soon as he saw Galileo's light. Galileo would then time how long it took before he saw the light from the other hilltop. However, his experiments took place over terrestrial distances and the timing methods available to him were far to crude to make a successful determination given such distances and the very great speed of light hence he was unable to measure the speed of light.

In 1676, Olaus Roemer, a Danish astronomer, first successfully measured the speed of light. Roemer's estimate for the speed of light was 220,000,000 metres per second.

His method: It was based on the observations of the eclipses of the moons of Jupiter. Roemer noticed, while observing Jupiter's moons, that the times of the eclipses of the moons of Jupiter seemed to depend on the relative positions of Jupiter and Earth. If Earth was close to Jupiter, the orbits of her moons appeared to speed up. If Earth was far from Jupiter, they seemed to slow down. Reasoning that the moons orbital velocities should not be affected by their separation, he deduced that the apparent difference must be due to the extra time for light to travel when Earth was more distant from Jupiter. Using the commonly accepted value for the diameter of the Earth's orbit, he came to the conclusion that light must have traveled at 220,000,000 metres per second.

In 1729, James Bradley used the aberration of light method to estimate the speed of light and he measured it to be 301,000,000 metres per second.

In 1849, Hippolyte Fizeau used the toothed wheel method to estimate the speed of light and he measured it to be 315,000,000 metres per second.

In 1862, Leon Foucault used the rotating mirror method to estimate the speed of light and he measured it to be 298,000,000 metres per second.

In 1907, Rosa and Dorsey used the electromagnetic constants method to estimate the speed of light and they measured it to be 299,710,000 metres per second.

In 1926, Albert Michelson used the rotating mirror method to estimated the speed of light and he measured it to be 299,796,000 metres per second.

In 1950, Essen and Gordon-Smith used the cavity resonator method to estimate the speed of light and they measured it to be 299,792,000 metres per second.

In 1958, K.D. Froome used the radio interferometry method to estimate the speed of light and he measured it to be 299,792,500 metres per second.

In 1972, Evenson et al. used the laser interferometry method to estimate the speed of light and he measured it to be 299,792,456.2 metres per second. The development of lasers with very high spectral stability and accurate caesium clocks made even better measurements possible.

In 1983, to further reduce uncertainty, the seventeenth CGPM replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of the second and the speed of light. This definition fixed the speed of light in a vacuum at precisely 299,792,458 metres per second.

Reflections:

I feel that all these people who tried to measure the speed of light is very creative as they were able to think of methods to measure it. I was also touched by their determination to try and measure the exact value of the speed of light. Many scientist in the past believed that light has a infinite speed and there is no way to measure it. However, it was Galileo who was willing to put in effort and try to measure the speed of light and even though he failed, it was a motivation for other scientists to try and measure the speed of light. The measurement of the speed of light has helped in many areas of physics and it is very important. This taught me that we should not give up but try to think of different methods to figure it out when sometimes it might seem to be impossible.

2011 Term 2 Reflections

I feel that term 2 was the hardest term. We learnt more about chemistry and physics. The topics we learnt were total internal reflection, refraction, chemical symbol and equations and acid and bases. I feel that chemical symbol and equations were the hardest. I had difficulties understanding them. It requires me to practice and memorize a lot to be able to understand. Acid and bases was quite challenging to me as there is quite a lot of things needed to be memorized like Acid + Base -> Salt + Water and Acid + Metal -> Salt + Hydrogen. As for reflection and refraction, I also had some difficulties understanding them especially drawing ray diagrams on the effects of refraction but after much practices, I managed to understand most of the concepts. I scored quite badly for this term test. It was because I was not able to understand the chemistry component. I guess this means that I need to work harder on that part. :'(

Light Bulbs

Incandescent light bulb

The incandescent light bulb is a source of electric light that works by incandescence, which is the emission of light caused by heating the metal filament to a high temperature until it glows.

Incandescent light bulbs:

are produced in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts.

mercury-free

require no external regulating equipment

have low manufacturing costs

compatible with control devices such as dimmers and timers

work equally well on either alternating current or direct current.

dimmers can be used to control brightness

have a lifespan of 750 hours or 1,000 hours

are highly inefficient, as over 98% of the energy input is emitted as heat, only 2% of its power input can be converted to visible white light

produces 13 to 18 lumens per watt

Compact Fluorescent light bulb

A fluorescent light bulb is a gas-discharge light bulb that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. While larger fluorescent light bulbs have been mostly used in commercial or institutional buildings, the compact fluorescent light bulb is now available in the same popular sizes as incandescents and is used as an energy-saving alternative in homes.

Compact Fluorescent light bulbs:

if breaks, exposure to hazardous mercury can occur

contains mercury which complicates their disposal

requires a ballast to stabilize the current through the light bulb, and to provide the initial striking voltage required to start the arc discharge. Energy lost in magnetic ballasts can be significant, on the order of 10% of its input power.

purchase price is typically 3 to 10 times greater than that of an incandescent light bulb

cannot be connected to dimmer switches intended for incandescent light bulb and for dimming installations, it requires a compatible dimming ballast

efficiency is affected by shape and size

efficiency decreases in much lower or higher temperature

when frequently switched on and off, it will age rapidly and under extreme conditions, its lifespan may be much shorter than a cheap incandescent light bulb.

have a lifespan of 6,000 to 15,000 hours, 8 to 15 times that of incandescents

use 20 to 33 percent of the power of equivalent incandescent light bulb for a given light output

convert about 22% of the power input to visible white light

heat generated by fluorescent light bulb is much less than its incandescent counterpart

energy is still lost in generating the ultraviolet light and converting this light into visible light.

produces 40 to 70 lumens per watt

LED light bulb

A LED light bulb uses light-emitting diodes (LEDs) as the source of light. LED is a “solid-state” technology, which means that the materials used to generate the light are encased within a solid material. LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light.

LED light bulbs:

offer lifespans of 30,000 or more hours, reduced if operated at a higher temperature than specified

require more precise current and heat management

mercury-free

available with a variety of color properties

higher purchase cost than other types

do not need ballast

improved robustness

smaller size

lower energy consumption

greater durability and reliability

are subject to very limited wear and tear if operated at low currents and at low temperatures

efficiency is not affected by shape and size

efficiency tends to decrease as one increases current

produces 20 to 60 lumens per watt

Reflections:

I learnt how each bulb produces light and the advantages and disadvantages of each bulb. Incandescent light bulbs are very cheap but it does not last long and much energy are wasted as most energy is emitted as heat. Compact fluorescent light bulbs on the other hand are not considered expensive and can last longer than incandescent light bulbs and also less energy are wasted as compared to incandescent light bulbs. Although the LED light bulbs are very expensive, it would last much longer than other bulbs and it can greatly reduce the amount of energy used. If I was given a choice, I would definitely choose the LED light bulbs as even though they cost a lot, my money would be worth it as their lifespan are very long , can save the most energy and is safe as it is mercury-free.

Rainbow

Rainbow

A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc. The colours of the rainbow are red, orange, yellow, green, blue, indigo and violet.

In a primary rainbow, the arc of a rainbow shows red on the outer (or upper) part of the arc, and violet on the inner section. This rainbow is caused by light being refracted then reflected once in droplets of water.

The light is first refracted entering the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40–42°. The angle is independent of the size of the drop, but does depend on its refractive index.

The speed of light in an optical medium is different for different wavelengths. When a beam of white light passes from air into an optically denser medium, all seven constituent coloured lights travel slower and undergo refraction. As a result of difference in speed, each wavelength slows down at different rates and are refracted at different angles upon entering and exiting the optical medium. This is how the dispersion of white light is achieved.

The amount by which light is refracted depends upon its wavelength, and hence its colour. This effect is called dispersion. Blue light (shorter wavelength) is refracted at a greater angle than red light, but due to the reflection of light rays from the back of the droplet, the blue light emerges from the droplet at a smaller angle to the original incident white light ray than the red light. Due to this angle, blue is seen on the inside of the arc of the primary rainbow, and red on the outside.

Double Rainbow

Secondary rainbows are caused by a double reflection of sunlight inside the raindrops, and appear at an angle of 50–53°. As a result of the second reflection, the colours of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself is spread over a greater area of the sky.

Reflections:

I feel that the topic on rainbow is very interesting. I learnt many things from this like the different types of rainbow, formation of the rainbow and the dispersion of light. I never heard or seen a double rainbow before. Although a dim secondary rainbow is often present outside the primary rainbow, most people will not notice it because they are not actively looking for it and also because it is fainter than the primary rainbow as more light escapes from two reflections. In the future, when I see a rainbow in the sky, I would definitely try to spot for the secondary rainbow.

2011 Term 1 Reflections

I find Secondary 2 a lot harder than Secondary 1. At the start of the year, I had difficulties understanding what is being taught. In Term 1, I learned more about chemistry. I learned about the atomic structure, ionic and covalent bonding and also word equations. As it was a new topic to me, at first I found it quite hard to understand, however, after many practices and help from my friends, I finally managed to understand most of it. I find that word equation is quite tough as it needs you to understand very well and also need a lot of practice. As for the term test, I think I did not so badly. However, there is still lots of room for improvement as I need to improve on the word equations. Until now, I still have some problems doing word equations hence this means that I would need to work double hard on that area.

Periodic Table

We learnt about the periodic table and the elements in this term. There are 8 groups in the periodic table. They are grouped according to their properties and the number of valence electrons they have. Group 1 and 2 are metals and group 8 is noble gases. The period are grouped according to the number of filled electron shells it have and also it increases in the number of valence electrons as the elements moves from left to right.

The number " 16 " on top is the mass number. The mass number is made up of the number of protons plus the number of neutrons. Isotopes are atoms from the same element and have the same number of protons and electrons but have different number of neutrons. The number " 8 " below is the atomic number. It is the number of protons the atom has. Normally, the number of protons would also be the same as the number of electrons. Ions are atoms when the number of electrons is not the same as the number of proton hence it would either be positive if it loses an electron or negative if it gains an electron.

Ionic Bonding and Covalent Bonding

Ionic bonding is a chemical bond between a non-metal and a metal. Metal would have lesser valence electrons and non-metal would have more valence electrons. Hence in order to get a full shell like the noble gases to be more stable, metal would lose its electrons, becoming positive, and non-metal would gain electrons, becoming negative. This process is called ionic bonding. Examples of ionic bonding are Na and Cl. Na would lose an electron and Cl would gain an electron to be able to form a stable full shell.

Covalent bonding is a form of chemical bonding between two non-metals. The two non-metals share their electrons to be able to have a stable full shell like the noble gases. Examples of covalent bonding are two hydrogen atoms. They have one atom each and hence would share with each other in order to have a complete shell of two electrons. This process is covalent bonding.