Semiconductor Diodes (Physics)

1. A semiconductor a material that can conduct electricity better than an insulator but not as good as a conductor (dia dok tengah-tengah).

2. Some examples of semiconductors are silicon, germanium and selenium.

3. 'Doping' a semiconductor means adding a small amount of other substances such as antimony or boron atoms to pure semiconductors to increase their conducting abilities.

4. So, when we add a little bit of boron to some silicon, the silicon is 'doped', and it can conduct electricity better than pure, unaltered silicon.

5. In this lesson, we are introduced to pentavalent atoms and trivalent atoms. What the hell are they?

6. A pentavalent atom is an atom that has five valence electrons. Example; phosphorus, antimony. A trivalent atom is an atom that has three valence electrons. Example; boron, gallium.

7. Semiconductors doped with penta atoms become n-type semiconductors. They have negative electrons as majority charge carriers.

8. If doped with tri atoms, they become p-type semiconductors. They have positive holes as majority charge carriers.

9. A diode is a device which allows current to flow through it it one direction only.

10. A semiconductor diode is basically a p-type and a n-type joined together.

11.Forward-biased= anode connected to positive terminal of battery, cathode negative. Reverse biased=vice versa.

12. Special power; diodes can be used a.c into d.c. This is called rectification.

13. A capacitor fuctions to smoothen the current that is rectified (ac to dc) by discharging current when diode is reversed biased.

First, Second, and Third Lines of Defence (Biology)

1. First and second lines of defence are inborn and non-specific.

2. Inborn means that these lines of defence are derived from inside our body, and non-specific means that these lines of defence attack many types of pathogens. *Pathogens are harmful and desease-causing microorganisms*

3. First line of defence is the skin and mucous membrane, while the second line of defence are phagocytes (white-blood cells).

4. Chemicals in the first line of defence include lysozyme (present in sweat, tears, saliva, and nasal secretion), sebum(secreted from skin), and mucus.

5. When pathogens succeed in penetrating the skin and mucous membrane, the second line of defence kicks in. Basically, its the process of phagocytosis.

6. common types of phagocytes are neutrophils and macrophages.

7. Simple description of phagocytocis; the phagocyte extends its plasma membrane around the pathogen, engulfing it. The pathogen trapped in a phagosome, which is a space inside the phagocyte. Lysosomes then attach to the phagosome and becomes phagolysosome. Pathogen inside the phagolysosome is digested by enzymes and acids. Waste is discharged from phagocyte.

8. Some Third line of defence terms; immunity, antigen, antibody, and lymphocytes.

9. Immunity is the ability of the body to resist infection. (immunity=ability)

10. Antigen (short for antibody generator) is a foreign protein molecule that stimulates the production of specific antibodies.

11. Antibody is a protein substance produced by the immune system in response to the recognition of a specific antigen.

12. Lymphocytes are also white blood cells. Specifically, B-lymphocytes produce the antibodies that destroy the pathogens.

a lymphocyte

13. The third line of defence is aqquired and specific, meaning that they are triggered by substances outside the body, and they are specific in their action of defence.

Soaps, Detergents

1. Whats a soap? In chemistry terms, a soap is a sodium or potassium salt of a fatty acid.

2. Basic formula for soap; RCOONa (for sodium soap) or RCOOK (for potassium soap). The R stands for the alkyl groups of carbon chain.

3. How to make soap? Saponification (Sa.po.nee.fee.kay.syen).

4. Ester + alkali = soap + glycerol.

5. Contoh: stearate(ester) + sodium hydroxide(alkali) = sodium stearate(soap) + glycerol.

6. Some names of soap: sodium stearate, sodium palmitate.




to be continued .........

Mercedes SLS; The Gullwing

At first I thought it was ugly. But, as time goes on, it started to look decent. Now, I can't take my eyes of of it. It's my new desktop wallpaper. When you say something grows on you, it refers to a situation wherein the first impressions didn't even catch your attention, but, as time passes, you take more notice of the thing, and you cannot help but appreciate what you missed in the beginning. Like, for example, you think a car looked like a dead frog when you first saw it, but eventually, you start liking the car, for reasons 'unexplainable'.

This car grew on me.

I don't know where to point. Maybe it's the doors, or the sharp grille. Probably the retro 50s design cues of the benz sl300. But definitely, the overall shape is brilliant.

The engine...hell big. 6.3 litres churning out 571 horses. I'm not really a horses counter. I believe perfection lies in the overall package of the car. But horses do help. Big engine plus lightweight plus grip plus unique styling equals Mercedes SLS AMG. The end.

Man, Jalil, I really don't get why you despise the looks of the SLS, you anti-Mercedes, BMW biased *******:P

Anyways, click the link http://www.autoblog.com/2009/09/11/everything-you-wanted-to-know-about-the-mercedes-sls-amg/ to read a little more about the SLS AMG and view the picture gallery.

Transformers (Physics Punya)

1. A transformer is an electrical device that increases or decreases an alternating voltage based on the principal of electromagnetic induction.

2. Electromagnetic induction pulak, is the production of an electromagnetic force in a conductor when there is relative motion of the conductor across a magnetic field.

3. EI ni ialah penghasilan daya (force) elektromagnet apabila konduktor bergerak dalam medan magnet.

4. Kita ada step up transformer dgn step down transformer.

5. Senang saja. Nak tau kata dia step up transformer, primary coil dia sikit, secondary coil banyak.

6. Nak tau kata dia step down transformer, primary coil banyak, secondary coil sikit.

7. The term 'ideal transformer' refers to a transformer that has equal output power and input power.

8. Efficiency of a transformer; (output power/input power)x100%.

9. Output power=secondary volt x secondary current. Input power=primary volt x primary current.

10. There are 4 main causes of heat loss in transformers. a)Resistance of copper wire. b)Eddy currents. c)Magnetization and demagnetization of core. d)Flux leakage. (FREM)

11. How to counter flux leakage? by winding primary and secondary coils closer to each other.

12. How to counter resistance of wire? by using thicker copper wire to reduce resistance, or by using cooling fins (sirip penyejuk) or coolants to reduce temperature of transformer.

13. How to counter eddy currents? by using a core made from thin plates of soft iron insulated from each other.

14. Lastly, how to counter magnetization and demagnetization? by using soft iron core which magnetizes and de* easily.

*What exactly is an eddy current? I honestly don't know. Someone good at explaining things please explain this term to me. Thank you.