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.