## Friday, October 23, 2009

### [Physics SPM] Exam Pointers III

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Source: Maths & Science Guide

Revision
1. Compare the separating distance between consecutive bright fringes of red light with that of blue light of the interference pattern obtained from a Young's double slit experiment.

2. State one observation of the interference pattern of red light in a Young's double slit experiment.

Frequent Mistakes

1. The interference of red light has a bigger number of fringes due to the smaller separating distance compared to that of blue light. This is because the wavelength of red light is bigger than that of blue light.

2. Bright and dark fringes are observed due to the interference of coherent waves.

1. The separating distance between consecutive bright fringes of red light is bigger than that of blue light.

2. Alternate bright and dark fringes are formed. The central fringe is the bright fringe. All the fringe sizes are equal, or the separating distance of consecutive fringes is the same.

## Wednesday, October 21, 2009

### [Physics SPM] Exam Pointers II

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Source: Maths & Science Guide

Revision

1. What are waves?

2. What is meant by "speed"?

Frequent Mistakes

• Waves are energy produced by oscillations that is able to transfer through medium and travel through vacuum.

1. Waves are the propagation of energy through the oscillation of particles of a medium.

2. It is the rate of change of distance. It is = (distance/time). When an object travels a distance of 20m in 10s, its speed is (20/10) = 2m/s. It is scalar quantity.

• The command phrase is "What is meant". Thus, you can choose to give the definition of speed, OR examples that provide the meaning of speed.

### [Chemistry SPM] Chemistry Term & Definition

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1. Isomers
Definition: Compound with the same molecular formula but different structural formulae.

2. Empirical Formula
Definition: The formula that gives the simplest whole number ratio of atoms of each element in the compound.

3. Electrolysis
Definition: A process that involves passing electricity through compounds in molten or aqueous state to break them down into their constituent elements.

4. Melting point
Definition: The temperature at which a solid changes into liquid form under a particular pressure.

5. Strong alkali
Definition: A chemical substance that ionises completely in water and produces a high concentration of hydroxide ions.

6. Unsaturated hydrocarbon
Definition: An organic compound that contains only carbon and hydrogen, as well as double or triple bonds between carbon atoms.

7. Redox reaction
Definition: A reaction that involves electron transfer or a change in oxidation number.

8. Activation energy
Definition: The minimum energy colliding reactant particles must have before collisions between them can result in a chemical reaction.

9. Strong acid
Definition: A chemical substance that ionises completely in water and produces a high concentration of hydrogen ions.

10. Rate of reaction
Definition: The charge in quantity of reactants and reaction products with time.

### [Physics SPM] Exam Pointers I

>>> Pakej Pembelajaran & Penilaian Online <<<
Source: Maths & Science Guide

Revision
1. Relate the inertia of an object to its mass.

2. Why does refraction of water waves occur?

3. What is observed when a mercury thermometer is placed in a hot water of 80°C?

Frequent Mistakes

1. The inertia of an object is directly proportional to its mass.

2. When a water wave travels from deep water to shallow water, it undergoes refraction.

3. Themal equilibrium is achieved.

1. The higher the mass, the higher is the inertia.

2. Because water waves undergo change in speed in the direction of propagation.

3. The mercury length increases to the 80°C mark./The mercury rises up the tube to the 80°C mark.

* Deeper water allows greater velocities while shallower water causes lower velocities.

## Tuesday, October 20, 2009

### [Physics Form 4] Lighting Up!

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1. How are we able to see an object?
Answer: When enough light falls on the object, incident light rays are reflected from its surface. The reflected light rays then enter our eyes and form an image on the retina. We are able to see the object when the brain interprets the image.

2. Must light be incident on an object? If objects cannot be seen in a dark room, how are we able to see a lighted bulb in it?
Answer: A lighted bulb is a primary light source that emits its own light. Hence, its incident light rays directly enter our eyes and form an image. On the other hand, objects that do not emit light rely on the reflected incident light rays to form an image in our eyes. These objects act as secondary sources of light.

3. Is the moon seen through the reflection of the sun's light that is incident on it?

## Sunday, October 18, 2009

### [Biology Form 5] Characteristics - Laws of Inheritance

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Gregor Mendel is highly attributed for his work in genetics. The father of genetic studied the inheritance of characteristics from the common garden pea plant, Pisum sativum, and was credited with discovering the two basic laws of inheritance: the law of segregation and the law of independent assortment.
1. All characteristics are controlled by pair of genes.

2. a) A characteristic is a distinctive inherited feature. Three examples of characteristics in:
• Plants - Height of plant, seed colour, seed shape.
• Animals - Eye colour, height, colour of fur/skin.

b) A trait is a variant for each characteristic. Two examples of traits in:
• Plants - Yellow colour of seed, wrinkled seed shape.
• Animals - Grey fur colour, green eyes.

3. A gene is a specific segment of DNA.

4. Two genes, each found on the same locus along a pair of homologous chromosomes, are needed to determine one characteristic.

5. Each member of the pair of genes determining a particular characteristic is called an allele.

6. A dominant allele is one which, when present, even singly, is strong enough to determine the phenotype. The two following conditions can allow a dominant allele to express itself in the phenotype.
a) Homozygous dominant: two dominant alleles present.
b) Heterozygous dominant: one dominant allele and one recessive allele present.

7. A recessive allele can only determine a phenotype if it is present on both homologous chromosomes.

## Friday, October 16, 2009

### [Biology SPM] Exam Pointers II

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Source: Maths & Science Guide

Revision
1. How do you separate blood into plasma and its cells?

2. Two types of land snails with brown and green shell colours are studied on a grassland habitat covered with dead woods, twigs and fallen leaves. State why quadrat sampling is inappropriate in the above investigation.

3. Name the substrate on which the enzyme lipase acts.

Frequent Mistakes

1. By centrifuging at high speed for a few minutes, the blood can be separated into plasma and its cells.

2. Quadrat sampling is time consuming and tedious to carry out.

3. Fats.
1. A sampling method is chosen based on the animal studied. The student should have made some reference to the land snails.

2. Fats are a smaller group of a larger family of lipids. Lipids include triglycerides (fats and oils), phospholipids and steroids.

1. By centrifuging blood at high speed for a few minutes. Subsequently, it separetes into two layers - the plasma layer on top and the cells at the bottom.

2. Since land snails are mobile organisms, they can move out of the quadrats. Hence, findings based on this technique will not be reliable.

3. Lipids.

### [Biology SPM] Exam Pointers I

>>> Pakej Pembelajaran & Penilaian Online <<<
Source: Maths & Science Guide

Revision
1. State the effect of an enzyme on an oil molecule.

2. State two conditions that denatures an enzyme.

3. State the conditions of the valves during atrial systole.

Frequent Mistakes

:
1. It converts it to fatty acid and glycerol.

2. Temperature and pH.

3. The valves close and the wall of the atria contract.
1. The word "convert" does not convey the information that it is done with water being the reagent, and that it is a breakdown process. The correct terminology should have been "hydrolyses".

2. The student stated temperature and pH but did not give an indication on whether both conditions should be high or low.

3. The keyword here is "the conditions of the valves". Students should know that there are two types of valves - atrio-ventricular valves (bicuspid and tricuspid valves), and semilunar bases at the aorta and pulmonary artery.

1. It hydrolyses it to fatty acids and glycerol.

2. Extreme temperature and extreme pH.

3. a) The semilunar valves close.
b) The bicuspid and tricuspid valves open.

## Thursday, October 15, 2009

### [Physics Form 4] Refraction

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• Refraction is the phenomenon exhibited by light when it undergoes a change in speed.

• Normally, when light travels through two different media of different optical density, it undergoes a change in speed and exhibits refraction.

• In most cases, refraction is seen as the bending of light or deflection of light from its original direction of propagation.

• There are two types of refraction:
1. Bending of light towards the normal, which occurs when light moves from a medium of lower optical density to higher optical density.
2. Bending of light away from the normal, which occurs when light moves from a medium of higher optical density to lower optical density.

## Tuesday, October 13, 2009

### Wonderful Salt

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Life without salt would be more than bland.

Salt either comes from evaporating seawater or is mined.

Most salt fields (spots of very salty water) are near the ocean. Nearby salt fields include those in Kampot, Cambodia an Nha Trang, Vietnam.

There are salt mines all over the world where people mine for rock salt. These mines are dried-up lakes and oceans. As the salty waters become enclosed or buried, the salt in the water turns into solid layers.

In the past, salt was so precious that salt roads were made, mostly to enable the transportation of salt to cities where there were no salt lakes or nearby seashores.

In certain cultures, salt was sacrificed to the gods. It was considered to have magical powers, too. Doctors would sprinkle wounds with salt in the hope of fighting off infection.

Today, say is sold in every shop and supermarket, and is more than a seasoning. Salt is used to make leather, roads, soap, glass, chlorine and paper.

It is also used to preserve hay and food, purify and soften water, refine metals, melt snow and ice, and freeze ice cream.

Salt is useful stuff, indeed!