Principle of Conservation of Energy

Another important physics principle that we learned in SPM is Principle of Conservation of Energy. In form 4 we've learned about these following energy;

i. Kinetic energy - energy due to movement ( 1/2mv^2)

ii. Gravitational potential energy - energy due to height or position of an object (mgh)

iii. Elastic potential energy - energy stored in an elastic material (1/2Fx)

iv. Heat energy (Q=mc@)

Meanwhile in form 5 u'll be learning the following energy:

i. Electrical energy (E=VIt)

ii. Nuclear energy

Ok..all these energy that u've learned will obey a physics principle called conservation of energy.

So what does this principle tells u??

Principle of conservation of energy states that;

1. energy can't be created or destroyed by human

2. energy can only be transformed from 1 form to another
3. total energy during the transformation is constant
Look at this video...

Statement 1 & 2 mean  we as human can only managed to transform those energy. For example a rotating fan transformed electrical energy into kinetic energy & some might escape  into heat.

Then applying statement 3, it means.. total initial energy= total final energy...

therefore...

 total electrical energy supplied = total of kinetic energy used + heat energy

In other words those energy trasformed in a rotating fan is conserved. If u noticed, the fan might cause some heat lost due to friction in its motor. So this heat is a wasted energy. By right a function of a fan is to rotate & let us feel cooler, not to make us sweat by releasing heat :)  .. If this is the case, we can say that the fan has some inefficiency in its job. 

Due to this reason we came across in a concept used to measure energy efficiency. 

Energy Efficiency = (output energy / input energy)  x 100

Efficiency's calculation is about getting the percentage. If we refer to case of the rotating fan again,  electrical energy supplied to the fan  is the input energy. Meanwhile the kinetic energy acts as its output energy. So by calculation,

Efficiency of the fan = [(Kinetic energy used) / (Electrical Energy) ] x 100

Let say from the calculation  its energy efficiency is about 80% . So mana pergi the balance 20 % ???? 

This is because 20 % of the energy has been wasted into heat. 

In real world its almost impossible to get a sytem or device that works 100% efficient. Even u as student  are not 100 % efficient :) ..Of course i will prove it to u...

• Let say in physic's exam, total given marks for paper 2 are 100 marks (i.e the input). 
• What u've answered correctly represents the output.
• Usually your output is less than 100 marks, or even worst whuch in some cases u dont even get more than 50 marks. 
• Thus your efficiency will be around 40 %. 

If thats the case, u should asked yourself mana hilang that 60% ?? .. u should keep asking what causes you to be so inefficient??? Identify those culprit that threatening u from becoming an efficient student....
Is it due to 'cinta monyet' things, or attitude problem?..or is it bcoz most of your time wasted due to your addiction towards internet unwanted activities such as too much social networking, gaming or pornography??? 

Once u've figure it out...i sincerely advice u to make a change b4 its too late   ..who knows with some attitude transformation u might be 90% efficient in November 2010. If u managed to do it..i'm pleased to say that an 'A+'  is within your grasp.

To summarize our today's discussion on conservation of energy, i highly recommend u to watch these videos..
Enjoy your revision ;)

Newton's 1st Law

Isaac Newton a 17th century scientist who is a very prominent figure in the world of physics. His theory & laws had been widely used till now and  it even helped  us to enjoy the rapid development of Formula 1 racing technology.
We are now living in a post IT society which is full of entertainment. We are able to do almost everything through online i.e playing games, facebook, shopping, watching movies etc. Those days in 17 th century, they don't have many entertainment as what we're having now. I would say the best entertainment for them are to seek more knowledge as possible. They don't have youtube, facebook, PS3, or among the worst Datuk T's pornographic movie. In other words they were not distracted with all these time wasting stuff.


Sometimes i 've been thinking that being a knowledgeable person at those days could be like a Hollywood artist. People will respect & adore them. In fact, this was the century where gifted persons like Isaac Newton, Galilieo Galilei, Blaise Pascal managed to revolutionalize their society towards seeking knowledge.That's why once they 've founded a principle or laws, they would place their names for us to appreciate until the end of time.

As for today, i want to discuss one of his laws that we will learn in SPM. It is the Newtons 1st Law of motion. Usually when we refer to this law,SPM students are more familiar with the term inertia. So what do this law tells us?
Newton's 1st law of motion often stated as:
An object at rest has tendency to stay at rest and object in motion stays in motion with thesame speed and in the same direction UNLESS there is unbalance force acting on it.


Allow me to make it easier for u to understand. Its like this, all objects tend to '"keep on doing what they're doing" unless there is 'unwanted Force' yang kacau. For example, imagine it's a school holiday and your mom try to wake you up solat subuh. In this case, u have a 'big tendency' to remain on your bed, unless your mom pour a bucket of water on your face :) ..So the bucket of water will be the 'unwanted force'


Let me give u another classic analogy. If u are a noble, honest & never watch pornography in your life, then u should maintain your 'inertia' i.e your dignity eventhough there is unwanted forces like 'Mr T' who tempted u to watch sex ,lies & video tape (:


To understand better on concept of inertia or Newton's 1st law of motion,u should watch all these videos.

SPM Physics: AC Generator

The different between AC & DC generator is:
-it consists of 2 slip rings instead of commutator
-slip rings allows current in outer circuit to flow in different direction

For better undertanding, watch how it moves in the video below..


The output induce current varies at different angle of the coil rotation. Observe the graph below.

• The current is zero when the coil is vertical. This is because the coil is parallel with magnetic field results in no magnetic field being cut. Thus no current is induced.

• The current is maximum when the coil is horizontal. At this point maximum rate of change or rate of cutting of the magnetic fields occur.

• You also must be able to differentiate the output graph of AC & DC generator. Click image below to see the diffrence.

SPM: Interference Q & A

Q1 : SPM 2003/P1 

The diagram shows the fringe pattern produced from Young’s double slit experiment using the monochromatic red light source. 
What happens to the fringes if monochromatic yellow light source is used? 

A. The bright fringes are wider than the dark fringes B. The dark fringes are wider than the bright fringes C. The distance between consecutive fringes decrease D. The distance between consecutive fringes increase

Ok to answer this one..u must remember the sequence of visible light (pelangi) spectrum.
it starts with red,orange,yellow,green,blue and so on.

from red to blue...the wavelength is decreasing,
So yellow wavellength is smaller,... by referring equation λ=(ax) /D ... 

λ is directly proportional with x, thus x (distance between fringes)will also decrease.

Answer = C

Q2 : SPM 2004/P1 

The diagram shows an interference pattern of two coherent water waves of sources, P and Q.
Which of the positions A, B, C or D, does destructive interference occur?

Answer: D

Q2 : SPM 2006/P1 

Diagram 20 shows the interference patterns for water waves from two coherent source, S1 and S2.

Which of the following superposition of the waves at
shows the point Y?




answer= A (crest +trough = destructive interference) 

Fish & Buoyancy

Today let's revise some form 4 topics on  Buoyant Force. In SPM, we learned that buoyant force depends on its volume of water displaced. The larger the volume displaced, the greater the buoyant force. Buoyant force also depends on density of the water, i.e greater water density produce greater buoyant force.

As i told u last time, learning physics will be interesting if u are able to blend its concept with nature & things around u. When i was a kid, i loved to keep fish as a pet and guppy was one of my favorites. Fish is very mobile in water. They are able to swim to the surface, stay in the middle of the water or sink to the bottom.

Ok how they did it.. I mean to float and sink?? Basically fish is able to do it through air filled bag called swim bladder. This bladder has nothing to do with its urine product. In fact swim bladder helps most fish to maintain its  buoyancy. To swim upward a fish fills the bladder with oxygen through the gills. When the bladder is filled with oxygen, the fish has a greater volume and its bladder is expanded. This displace more water and so it experiences a greater buoyant force.

In order to sink,air is removed from the bladder that causes decrease in its volume. Thus its average weight will be greater greater than buoyant force which then pull it towards ocean floor.

To float at certain level, the bladder is filled with air until it displaces a volume of water to produce a buoyant force that equal to its weight. In this case, the weight & buoyant force are in equilibrium. Thus it stays at that level. The same concept is applied in submarine except submarine needs a ballast tank to increase or decrease its buoyancy by adding or removing sea water inside it.