Physics Form 4: Chapter 3 - Liquid Pressure

Liquid pressure is due to the weight of liquid acting on the surface of any objects in the liquid.

P = Pressure

h = depth
ρ = density of liquid
g = Gravitational Field Strength

Liquid pressure increases with depth. The deeper the object in the liquid, the higher the pressure exert on the object.

Pressure acts in all direction perpendicularly to the surface area of the object.

 Pressure in liquid does not depends on

- the size of the container.

- the area of its surface 

- the shape of the container

Pressure in liquid depends only on its vertical distance from the surface of the liquid.

Pressure at A = Pressure at B

JPA offers 4,000 scholarships to SPM holders

Written by Bernama
Monday, 13 June 2011

KUALA LUMPUR: The Public Service Department (PSD) has offered 1,500 scholarships under the overseas degree programme (PILN) and 2,500 scholarships under the local degree programme (PIDN) for Sijil Pelajaran Malaysia (SPM) 2010 holders. Minister in the Prime Minister's Department Datuk Seri Mohamed Nazri Aziz said on Monday, June 13 882 Bumiputera students and 618 non-Bumiputera students received the scholarships under the PILN.

For the local degree programme this year, 1,301 Bumiputera students and 1,199 non-Bumiputera students received scholarships, he said during the question-and-answer session in the Dewan Rakyat, here. Nazri said the 10 per cent allocation for Sabah and Sarawak Bumiputera students remained, with 75 from Sabah offered scholarships for studies overseas under this category. Besides that, he said, Sabah's students were offered study sponsorship overseas under the Academic Excellence category, bringing the total number of Sabah students sponsored under the PILN in 2011 to 77.

"The government has allocated RM1.44 billion for PSD sponsorship this year of SPM 2010 holders, with RM0.36 billion of the sum for studies at local higher learning institutions and RM1.08 billion for studies abroad." Nazri said among the reasons for many excellent students not being offered scholarships to study overseas was the increased number of top scorers and imited government funds.

"There were also many bright students choosing popular fields of study like medicine and engineering compared to arts and science, causing them not being offered scholarships to study overseas as the offer also depends on the public sector and country's manpower needs. "The PSD will review and improve the existing policy in the future to avoid the scholarship offers from becoming an issue each year."

Chemistry Form 4: Chapter 6 - Electrolysis of Lead (II) Bromide

• Electrolysis is a chemical process where a substance in its molten state or in an aqueous solution decomposed by electric current.
• This involves conversion of energy from electrical energy to chemical energy.
• Electrodes are the strips of metals inserted into electrolyte for conduction of electricity. he metal electrode connected to the positive terminal of the battery is called the anode (+). The metal electrode connected to the negative terminal of the battery is called the cathode (-).
• Electrolytic cell is the complete set-up for electrolysis. This consists of the vessel containing the electrolyte, anode, cathode, battery and  wires. 

At the Cathode	At the Anode
Observation When electricity is flowing, a silvery deposit of lead metal forms on the cathode. In fact, as it is molten, it is more likely to drip off in a molten blob.	Observation When electricity is flowing, brown fumes of bromine gas are seen at the anode.
Half equation Pb2+ + 2e ---> Pb	Half equation 2Br- ---> Br2 + e
Explanation The lead(II) ions, as they are positive, move to the negative cathode, where each ion gains two electrons to form a lead atom. Any reaction at a cathode involved  a gain in electrons. This is called reduction or more exactly, cathodic reduction .	Explanation The bromide ions, as they are negative, move to the positive anode, where each loses an electron to form a bromine atom. Then two of these newly formed atoms combine to form bromine gas. Any reaction at an anode involves a loss of electrons.

Physics Form 5: Chapter 3 - Transformer

Transformer is an electrical device which increases and decreases an alternating voltage. Transformer only works with alternating current

How transformer works:

• A transformer works on the principle of electromagnetic induction.
• When the a.c voltage, V_p is applied to  the primary coil, an alternating current flows through the coil. The soft iron core is magnetized in one way and then the other.
• This causes a changing magnetic flux to pass through the secondary coil producing an a.c voltage V_s.  

 

Types of transformer:

1. Step up transformer:  The number of turns in the secondary coil is more than the number of turns in the primary coil. Output voltage is higher than the input voltage.
2. Step down transformer: The number of turns in the primary coil is more than the number of turns in the secondary coil.

Click on the diagram below to play!

Chemistry Form 5: Chapter 3 - Rules of Oxidation Number

There are several rules for assigning the oxidation number to an element. Learning these rules will simplify the task of determining the oxidation state of an element, and thus, whether it has undergone oxidation or reduction.

1. The oxidation number of an atom in the elemental state is zero.
   Example: Cl₂ and Al both are 0 
2. The oxidation number of a monatomic ion is equal to its charge.
   Example: In the compound NaCl, the sodium has an oxidation number of 1+ and the chlorine is 1-.
3. The algebraic sum of the oxidation numbers in the formula of a compound is zero.
   Example: the oxidation numbers in the NaCl above add up to 0
4. The oxidation number of hydrogen in a compound is 1+, except when hydrogen forms compounds called hydrides with active metals, and then it is 1-.
   Examples: H is 1+ in H₂O, but 1- in NaH (sodium hydride).
5. The oxidation number of oxygen in a compound is 2-, except in peroxides when it is 1-, and when combined with fluorine. Then it is 2+.
   Example: In H₂O the oxygen is 2-, in H₂O₂ it is 1-.
6. The algebraic sum of the oxidation numbers in the formula for a polyatomic ion is equal to the charge on that ion.
   Example: in the sulfate ion, SO₄^2-, the oxidation numbers of the sulfur and the oxygens add up to 2-. The oxygens are 2- each, and the sulfur is 6+.

Physics Form 4: Chapter 2 - Force Acting on a Skydiver

When an object falls, it accelerates. As its speed increases, the air resistance increases.
Eventually, the force from the air resistance will equal the force from the weight of the object.
At that point, the speed will remain constant: the object has reached its "terminal velocity" and can't fall any faster.

Click on the diagram below to play!

Physics Form 4: Chapter 3 - Pressure

• Pressure is defined force per unit area applied in a direction perpendicular to the surface of an object
• The unit of pressure is Pascal.

• The larger the area of surface, the lower the pressure exerted on an object.
• The greater the force, the higher the pressure exerted on an object.

 Application of pressure:

When the area is small, a moderate force can create a very large pressure. This is why a sharp knife is good at cutting things: when you push the very small area of the sharp blade against something, it creates a really large pressure.

Supermodel can damage floors by walking on then in high-heeled shoes. This is because the area of the heel is small, so you can easily create enough pressure to cause a dent in the floor.

Camels have large feet to increase surface area of contact with sand. Pressure produced is small. This is why a heavy camel will not sink into sand while walking on dessert.

Chemistry Form 4: Chapter 6 - Electrolyte

• Electrolyte is a chemical substance which conducts electricity in the molten or aqueous state.

• Electrolytes are able to conduct electricity because there are freely move ions in the molten or aqueous state.
• Examples of electrolyte are salt solution, dilute acids and dilute alkalis 

Click on the diagram below to play!