Physics Form 4: Chapter 4 - Boyle's Law of Gas

Boyle's law states that the pressure of a fixed mass of gas is inversely proportional to the volume of gas provided the temperature of the gas is constant.

The law was first proposed in 1662 by Robert Boyle

Because pV = constant that means that p₁V₁ = constant and so does p₂V₂. We can therefore write:

 

where

V₁ = equals the original volume,

V₂  = equals the new volume,

p₁  = the original pressure, and

p₂  = the new pressure.

Explanation of Boyle's law by the kinetic theory:

 

• At constant temperature, the average kinetic energy of the gas molecules is constant.
• When the gas is compressed, the volume is decreased. Therefore, the number of molecules per unit volume will increase.
• The rate of collision of the gas molecules with the wall of container will increase.
• Thus, the pressure of gas increases.

Physics Form 5: Chapter 5 - Application of Radioactive (Carbon-14 Dating)

C-14 is another radioactive isotope that decays to C-12. This isotope is found in all living organisms. Once an organism dies, the C-14 begins to decay. The half-life of C-14, however, is only 5,730 years. Because of its short half-life, the number of C-14 isotopes in a sample is negligible after about 50,000 years, making it impossible to use for dating older samples. C-14 is used often in dating artifacts from humans.

(Real mummy from Ramesses II)
How old is he ..............?

 

For determining age of fossils older than 60,000 years one uses a potassium-argon dating technique. Potassium dating has a half life of 1.3 billion years, thus allowing the age of rocks several billions years old to be determined. A more accurate "argon-argon" dating technique (determining the ratio between argon-39 and argon-40) has also been developed.

6 Principles of Life on MONEY

 1.   No point using limited life to chase after unlimited money.

 2.   No point earning so much money you cannot live to spend it.

 3.   Money is not yours until you spend it.

 4.   When you are young, you use your health to chase your wealth; when you are  old, you use your wealth to buy back your health. The difference is that it is too late.

 5.   How happy a man is, is not how much he has but how little he needs.

 6.   No point working so hard to provide for the people you have no time to spend with.

Chemistry Form 4: Chapter 7 - Strength of Alkali

The strength of alkali depends on the degree of dissociation of the alkali in water to produce hydroxide ions. The pH of an alkali solution depends on the concentration of hydroxide ions.

Strong Alkali	Weak Alkali
·     Strong alkali have a higher degree of dissociation. ·     A strong alkali is an alkali which dissociates completely in water to produce a high concentration of hydroxide ions. ·     Thus, pH value for strong alkali is higher than weak alkali.	·     Weak alkali have a lower degree of dissociation. ·     A weak alkali is an alkali which ionises partially in water to produce a low concentration of hydroxide ions. Only a part of the molecules ionises and the remaining still in covalent molecules. ·     Thus, pH value for weak alkali is lower than strong alkali.

Click on the diagram below to play!

Chemistry Form 4: Chapter 7 - How to Differentiate Between Strong Acid and Weak Acid

A) Reaction between acids and reactive metals

• Strong acids can react with reactive metal faster and more vigorously. More hydrogen gas produced at a faster rate.
• Weak acids can react with reactive metal slower and less vigorously. Less hydrogen gas produced at a slower rate.

B) Electrical conductivity

 

Conductivity Behavior of Acids
Compounds	Appearance of light bulb	Classification Weak or Strong	Inference of Ions or Molecules
water, H2O	no light	weak	molecules
hydrochloric acid, HCl	bright	strong	ions
acetic acid, HC2H3O2	dim	weak	mostly molecules, less ions

• Strong acids able to conduct electricity better as shown in hydrochloric acid because it contains a large number of freely moving ions as strong acids dissociate completely in water.
• Weak acids conduct electricity weakly as shown in acetic acid because it contains a few number of moving ions as weak acids dissociate partially in water. Most of weak acids still remain in covalent molecule.

Physics Form 4: Chapter 4 - Latent Heat

Latent heat is the quantity of heat absorbed or released by a substance to change its physical state without any change in temperature.

 

• Specific latent heat of fusion is the quantity of heat needed to change 1kg of a solid to liquid at its melting point without change in temperature.
• The temperature does not change even though heat is being absorbed by the solid particles. This is because the heat absorbed does not increase the kinetic energy of particles but is used to overcome the force of attraction between the particles.

• Specific latent heat of vaporization is the quantity of heat needed to change 1kg of a liquid to gas at its boiling point without change in temperature.
• The temperature does not change even though heat is being absorbed by the liquid particles. This is because the heat absorbed does not increase the kinetic energy of particles but is used to overcome the force of attraction between the particles.

 

Specific latent heat of vaporization is greater than its specific latent heat of fusion because:

• More energy is required to break the bonds between liquid molecules in order to change into gas phase.
• Extra energy is required to overcome atmospheric pressure.
• Energy is used to overcome the surface tension of a liquid when its molecules change into the gas phase.

   
Further information about latent heat

Physics Form 5: Chapter 5 - Half Life of Radioisotopes

• Half life is the time taken for radioisotope to decay to half of its original quantity. 
• Different radioisotope have different value of half life.

The half life formula is an exponential equation:

where N_t is the remaining substance after time t, N₀  is the initial amount of the substance, t_1/2  is the half life of the substance, and t is the elapsed time.

Click on the diagram below to play!

 

Radioisotope will continue to decay to form new atom until it becomes stable

Malaysian U in QS World University Rankings.

KUALA LUMPUR, Sept 5 — Universiti Malaya (UM), Malaysia’s oldest institution of higher learning, leapt 40 spots this year to breach the top 200 mark in the London-based QS World University Rankings.
But at rank 167, UM lagged more than 100 paces behind Singapore’s National University of Singapore (NUS) and Nanyang Technological University (NTU), which ranked at 28 and 58 respectively.

Apart from UM, the only Malaysian university that made it as the world’s top 300 universities was Universiti Kebangsaan Malaysia (UKM) at rank 279, dropping 16 spots from last year’s rank of 263. The QS World University Rankings currently considers over 2,000 and evaluates over 700 universities in the world. The rankings assess factors including academic reputation, employer reputation, graduate employability, research and staff-student ratios.

QS (Quacquarelli Symonds) Ltd Intelligence Unit head Ben Sowter was quoted in English daily The Star today as saying that UM was the only Malaysian university to have improved in its academics, employer scores and international aspects. According to the daily, Sowter said UKM had faltered in the employer reputation review and citations per faculty but improved in terms of academic reputation.
Going by academic reputation alone, the QS list ranked UM at 176 while Universiti Sains Malaysia (USM) made it to 209, ahead of UKM at 220.

The Star also quoted Higher Education Minister Datuk Seri Mohamed Khalid Nordin as saying that UM’s improvement was a reflection of the university staff’s hard work. In the world rankings list, USM made it to the 335th spot compared to 309 last year while Universiti Putra Malaysia (UPM) ranked at 358, dropping from 319 last year. UK’s Cambridge University held on to the top spot in the international league table, followed by United States’ Harvard University and Massachusetts Institute of Technology, Yale University and UK’s Oxford University.

The highest ranked Asian universities in the same table are the University of Hong Kong at 22, University of Tokyo at 25 and NUS at 28. In the Asian University Ranking 2011 by QS, UM made it to the 39th spot, ahead of UKM at 53, USM at 54, UPM at 57 and Universiti Teknologi Malaysia (UTM) at 76.
Topping the list was the Hong Kong University of Science and Technology, followed by the University of Hong Kong and NUS. Singapore’s NTU made it to rank 17.