Saturday, July 30, 2011

Physics Form 5: Chapter 4 - Transistor as an Amplifier

An amplifier circuit

IB = base current
IC = collector current
IE = emitter current
VBB = base voltage 
VCCcollector voltage

The function of resistant RB is to control and limit the base current.

How transistors function as an amplifier:
  • The forward-bias from base to emitter narrows the base-emitter,BE depletion layer.
  • The reverse-bias from base to collector widens the base-collector, BC depletion layer.
  • The free electrons from emitter diffuse easily through the forward-biased BE junction into the p-type region.
  • The base region is lightly doped and very thin, so it has a limited number of holes. Therefore, only a small percentage of the all electrons flowing through BE junction can combine with the available holes in the base region.
  • Most of the electrons do not combine with holes but diffuse into BC depletion layer.
  • Once here, these electrons are pulled through the reverse-biased BC junction by the electric field set up by the force of attraction between the positive and negative ions.
  • Electrons now move through the collector region and into the positive terminal of the collector voltage source.
  • This forms collector current which is larger than the base current.

Click on the diagram below to play!

When there is a small change in the base current, there will be a big change in the collector current. 

Chemistry Form 5: Chapter 3 - Redox Reaction in Electrochemistry Reaction

  • More electropositive metal undergoes oxidation reaction by releasing electrons and act as a reducing agent.
  • Less electropositive metal undergoes reduction reaction by gaining electrons and act as a oxidising agent.
  • Electrons flow from more electropositive metal to less electropositive metal.

Thursday, July 28, 2011

Physics Form 5: Chapter 4 - How Transistor Works

The design of a transistor allows it to function as an amplifier or a switch. This is accomplished by using a small amount of electricity to control a gate on a much larger supply of electricity, much like turning a valve to control a supply of water. 
Transistors are composed of three parts – a base, a collector, and an Transistor terminalsemitter. 

Base = gate controller device for the larger electrical  supply.
Collector = larger electrical supply.
Emitter = outlet for electrical supply.

By sending varying levels of current from the base, the amount of current flowing through the gate from the collector may be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier. The same process is used to create the binary code for the digital processors but in this case a voltage threshold of five volts is needed to open the collector gate. In this way, the transistor is being used as a switch with a binary function: five volts – ON, less than five volts – OFF. 

Still Can't Understand How Transistor Works! 

Try this imagination! 

We provide a reservoir of water for "C" (the "power supply voltage") but it can't move because there's a big black plunger thing in the way which is blocking the outlet to "E". The reservoir of water is called the "supply voltage".

If we increase the amount of water sufficiently, it will burst our transistor just the same as if we increase the voltage to a real transistor. We don't want to do this, so we keep that "supply voltage" at a safe level.

If we pour water current into "B" this current flows along the "Base" pipe and pushes that black plunger thing upwards, allowing quite a lot of water to flow from "C" to "E". Some of the water from "B" also joins it and flows away.

If we pour even more water into "B", the black plunger thing moves up further and a great torrent of water current flows from "C" to "E".

Physics Form 4: Chapter 3 - Application of Bernoulli Principle ( Aerofoil )

A cross section of a typical airplane wing will show the top surface to be more curved than the bottom surface. This shaped profile is called an aerofoil or airfoil. 
Due to this aerofoil structural design, the difference pressure below and above the aerofoil able to produce a larger lifting force.

According to Bernoulli Principle:
  • Air moves with higher speed over the top of aerofoil.
  • This creates a region of lower pressure over it and a region of higher pressure below it.
  • This difference in pressure produce a resultant force acting upwards on the wings.

Drag is the resistance of air (the backward force), thrust is the power of the airplane's engine (the forward force), lift is the upward force and weight is the gravity downward force.

When it is in straight and level flight the opposing forces of lift and weight are balanced. During a descent, weight exceeds lift and to slow an airplane drag has to overcome thrust. 

Chemistry Form 4: Chapter 6 - Constructing Electrochemical Series based on the Potential Difference between Two Metals

  • In a voltaic cell, two different metals are used to create a potential difference.
  • A higher metal in the electrochemical series will be made negative terminal.
  • A lower metal in the electrochemical series will be made positive terminal.
  • Conversion of energy is chemical energy to electrical energy.

Metals which are further apart in the electrochemical series produce a higher voltage than metals which are close to each other.

 By arranging the metals in order of their voltage readings, you can build up the electrochemical series.

Click on the diagram below to play!

Wednesday, July 27, 2011

Penang Assam Laksa Top 10 Global Food

Penang are proud to have Datuk Lee Chong Wei as World No.1 badminton man's single player, Datuk Nicol David as World No.1 squash woman's player, Jimmy Choo as world renowned shoe designer and many more towering Penangites who make Penang famous..

Now, we have Penang aunties and uncles who cook wonderful and delicious street food making Penang on the world map again. Without them, we will not have a chance to eat delicacy food such as assam laksa, har me, char kuey tiao, lobak, pasembur, hokkien me, bak kut teh, nasi kandar and so on. Thank you so much. Ah yi and Ah chek!

Let's we protect and promote our street food heritage!

KUALA LUMPUR, July 25 — Spicy, sour, fruity and fragrant, Penang assam laksa was voted seventh out of 50 most delicious food in the world in a global poll that leaned heavily towards Asian flavours. Malaysia’s sole entry beat out Indonesia’s beef rending (No 11) and Singapore’s twin national dishes, chicken rice (45) and chilli crab (35), but fell behind Thailand’s massaman curry, which took top spot.

The recent CNN Go feature did not say how it came up with the list, apart from saying its writers had “scoured the planet” for what they thought were the top 50 “foods worth travelling the world to gorge on”. “Poached, flaked mackerel, tamarind, chili, mint, lemongrass, onion, pineapple . . . one of Malaysia’s most popular dishes is an addictive spicy-sour fish broth with noodles (especially great when fused with ginger), that’ll have your nose running before the spoon even hits your lips” was how the online lifestyle feature described Penang assam laksa.

But Malaysia’s northern neighbour appeared highly popular with the CNN Go writers, as it saw four different dishes finding its way into the list. Apart from the massaman bestseller, Thailand also scored top marks for tom yum goong (No 8), nam tok moo, a meaty dish of grilled pork and toasted rice (No 19), and its signature green papaya salad, som tam (No 46).Other Southeast Asian offerings include Vietnam’s pho (No 28) and goi cuon, a rice-paper roll of shrimp, herbs, rice vermicelli and other ingredients, much like Malaysia’s poh-pia. The top 50 also feature a number of “national foods” such as sushi from Japan and Britain’s fish and chips.

Sunday, July 24, 2011

Physics Form 4: Chapter 3 - Application of Archimedes Principle (Plimsoll Line)

Plimsoll line is a mark on a vessel’s side indicating the maximum depth to which it may be safely immersed when loaded with cargo.

The maximum safe loading depth varies with ocean regions and seasons. In the tropics the water is warmer and therefore less dense than in temperate regions, so with the same load ships will float higher in cold regions than in the tropics. Summer and winter cause similar changes.
  • The density of water is determined by the salinity of water at different locations
  • A ship will submerge deeper in freshwater than that in sea water because the density of freshwater is smaller. 
  • The ship can be loaded with heavier load in sea water than in freshwater.

Thursday, July 21, 2011

Physics Form 4: Chapter 3 - Bernoulli Principle

  • Bernoulli principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases.
  • Fluid can be in liquid or gaseous state.
V2 > V3 > V1
P1 > P3 > P2

Click and drag the yellow handles to play!

Bernoulli animation link

Higher Speed , Lower Pressure
Lower Speed , Higher Pressure

Thursday, July 14, 2011

Good Thoughts

Heavy rains remind us of challenges in life. Never ask for a lighter rain. Just pray for a better umbrella. - That is attitude.
When flood comes, fish eat ants and when flood recedes, ants eat fish.  - Only time matters. Just hold on, God gives opportunity to everyone! 
Life is not about finding the right person, but creating the right relationship, it's not how we care in the beginning, but how much we care till the very end. 
Some people always throw stones in your path. It depends on what you make with them. A Wall or a Bridge? - Remember you are the architect of your life. 
Search for a beautiful heart, but don't search for a beautiful face. Coz beautiful things are not always good, but good things are always beautiful. 
It’s not important to hold all the good cards in life. But it’s important how well you play with the cards you hold.
Often when we lose all hope & think this is the end, God smiles from above and says, 'relax dear it’s just a bend, not the end.' - Have faith and have a successful life.
One of the basic differences between God and humans is, God gives, gives and forgives. But the human gets, gets, gets and forgets.

Physics Form 5: Chapter 4 - Components of Cathode Ray Oscilloscope

Cathode ray oscilloscope, CRO is used:
  • To display waveform of waves
  • To measure the potential difference
  • To measure short time interval
  • To test electronic equipments

A voltage applied to the x-plates can pull the electron beam side to side (along the x-axis), and a voltage applied to the y-plates can pull the electron beam up and down (along the y-axis). Vacuum inside the CRO tube is to allow electrons to move freely.

How we produce a colour TV?

Click on the diagram below to play!

Wednesday, July 13, 2011

Chemistry Form 5: Chapter 3 - Redox Reaction in Displacement of Metal

Reactivity Series of metals
Displacement of metals from solution is a redox reaction whereby a less reactive metal ion is displaced from its salt solution by a more reactive metal. As a result, the less reactive metal ion is deposited as a solid metal while the more reactive metal dissolves in the solution.

The general formula for a displacement reaction is:

M (s) + Xn+ (aq)  ----->   Mn+ (aq) + X (s)

where metal M is the more reactive than metal X.

Most reactive
Least reactive

Example of displacement reaction:

Fe (s) + CuSO4 (aq)     ----->     FeSO4 (aq) + Cu (s)

Iron displaces copper from the solution because it is more reactive than copper metal. Iron, being more reactive, loses its electrons readily. The electrons are transferred from the iron atoms to the copper(II) ions in the solution. Copper(II) ions are reduced to copper metal and iron atoms become oxidised to iron (II) ions. Iron acts as reducing agent whereas copper (II) ions act as a oxidising agent. 

Oxidation reaction:     Fe (s)     ----->     Fe2+ (aq) + 2e-
Reduction reaction:    Cu2+ (aq) + 2e-     ----->     Cu (s)
Overall Redox reaction:   Fe (s) + Cu2+ (aq)     ----->   Fe2+ (aq) + Cu (s)

Click on the diagram below to play!

Tuesday, July 12, 2011

Chemistry Form 4: Chapter 6 - Daniell Cell

Daniell cell is also known as Galvanic cell which using same working principle as voltaic cell. It converts chemical energy to electrical energy. Daniell cell is a part of a battery consisting of two metals joined by a salt bridge or a porous pot.

  • More electropositive metal acts as negative terminal which undergoes oxidation process (release electron)
  • Less electropositive metal acts as positive terminal which undergoes reduction (gain electron).
  • Electron flow from negative terminal to positive terminal.
  • The function of salt bridge or porous pot is to allow the movement of ions to pass through it to complete electrical circuit. Another function is to separate two electrolyte solutions. 
  • Examples of salt bridge are sodium chloride or potassium nitrate.

At Negative Terminal: More electropositive metal ( Zinc )

Observation:  Zinc plate dissolves or becomes thinner, its mass decreases
Half chemical equation :     Zn  ------>     Zn2+   +    2e

At Positive Terminal: Less electropositive metal ( Copper )
Observation:  Copper plate becomes thicker
Half chemical equation :     Cu2+     +    2e   ------>    Cu

Click on the diagram below to play!

Thursday, July 7, 2011

Wednesday, July 6, 2011

Chemistry Form 4: Chapter 6 - Extraction of Aluminium From its Ore

The ores of aluminium is called bauxite. Bauxite is a composition of aluminium oxide, (Al2O3).

The position of aluminium in the reactivity series indicates that, it could not be extracted by reducing the oxide using carbon or carbon monoxide. Electrolysis of molten aluminium oxide ("alumina") will, however, give aluminium and oxygen.

A = carbon anode       B = molten aluminium    
C = molten aluminium oxide and cryolite     D = carbon cathode  
  • The function of cryolite is to lower the melting point of aluminium oxide.
  • Aluminium metal forms at the cathode electrode and sinks to the bottom of the tank, where it is tapped off.
  • Oxygen forms at the anode electrodes. This oxygen reacts with the carbon of the anode electrodes, forming carbon dioxide, and they gradually burn away. Consequently, the anode electrodes have to be replaced frequently.

Tuesday, July 5, 2011

Physics Form 5: Chapter 4 - Thermionic Emission

  • Thermionic emission is the release of electrons from a heated metal.
  • The electrons in the metal gain kinetic energy from heat. Electrons that gain sufficiently high kinetic energy will be able to escape from the surface of metal.

  • The tungsten filament act as cathode
  • Cathode ray is a beam of electrons moving at high speed in vacuum.

    Saturday, July 2, 2011

    Physics Form 4: Chapter 3 - Pascal Principle

    • Liquid cannot be compressed, thus its pressure only can be transmitted to all direction with equal magnitude.
    • Pascal principle states that the pressure in a liquid is transmitted equally to all direction throughout enclosed liquid.

    Pressure at small piston = Pressure at large piston

    Friday, July 1, 2011

    Chemistry Form 5: Chapter 3 - Rusting of Iron

    • Rusting is a corrosion of iron.
    • For iron to rust, oxygen and water must be present.
    • In the presence of acids and salts, rusting occurs faster because these substances increase the electrical conductivity of water, making water a better electrolyte. 
    • Oxygen acts as the oxidizing agent and iron acts as the reducing agent.

    ·     The surface of iron at the middle of the water droplet serves as the anode at which oxidation occurs. The iron atoms lose electrons to form iron (II) ions.

    ·     The electrons flow to the edge of the water droplet where there is plenty of dissolved oxygen. The iron surface there serves as cathode at which reduction occurs. Oxygen gains the electrons and is reduced to hydroxide ions.

    ·     The iron (II) ions produced combine with the hydroxide ions to iron (II) hydroxide. The Fe(OH)2 is then further oxidized by oxygen to form iron (III) oxide, Fe2O3 known as rust

    Chemistry Form 4: Chapter 6 - Purification of Metal

    • The anode is a impure copper.
    • The cathode is a pure copper.
    • When electricity is passed through the cell, the copper is dissolved at anode where Cu2+ ions go into solution. Anode copper becomes thinner.

    • At cathode, copper ions are selectively discharge and deposited. Cathode copper becomes thicker.

    The blue intensity of solution remains unchanged because concentration of copper (II) ions in the solution remains unchanged. The rate at which copper enter into electrolyte from anode is equal to the rate at which the copper ions discharged at cathode.