Oh! Why Don't I Have Three Hands !

In this last part of unit 5, we deal with anything related to magnet. Many of you are confused with the Right-hand and the Left-hand rule. Well, it would be clearer if you can divide them into 3 main categories.

1. Magnetic-fields production :-

In this section, you use the grasping hand rule ( right hand only)
(a) Straight wire carrying a current : use thumb to follow the flow of current in the wire and the closing fingers the direction of the field lines (no north or south poles).
(B) A coil or solenoid (including Eddy current): Use the closing fingers to follow the flow of current ( because it is circular) and the thumb will point to the north pole. (imagine you are inside the bar magnet).

2. Producing motion

In this section, a power source is provided, so it is a motor. Electricity is doing the work for you, so you don't need a strong hand, you left hand will do. So, it is the Flemming's Left Hand Rule here. A current carrying conductor in a magnetic field will produce a magnetic force acting on the conductor. An electron beam moving in a magnectic field will produce a magnetic force acting on the individual electron and this force provides the centripetal force to make the electrons moving in a circle. BUT, a current carrying straight conductor alone will not produce a force in its own magnetic field. It must be in someone else's magnetic field for the force to be produced.

3. Current producing action

Here,mechanical energy is converted to electricity. You need a strong hand to produce electricity,hence the right hand. So you use Flemming's Right Hand Rule for this. The situations include flying aeroplane (horizontally and north-south direction) cutting through the vertical components of the Earth's magnetic field. No emf will be produced for cutting the horizontal components because there is no change in the flux line cutting the wing.

Hope the above will help.

On The Springboard

The syllabi of all the subjects has come to an end and all of you are on the springboard, waiting for the final dash to achieve your goals. I can't say about the topics because many of you are still waiting and planning to peak at the right time. But for Physics practical, I have a few things to say and hope that it will help you on.

Whenever the question ask " to what extent do your readings confirm ............." , YOU HAVE to find "the % Difference" and then compare to either "the sum of the % uncertainty of various measurements" or the standard "10%". But you should consider the first option first since you are now in Unit 5 and NOT unit 3 practicals, unless it is complicated to do the first option. In the last practical, MANY of you use the phrase ALMOST the same. As I said, you have to use figure to proof your points.

No of oscillations is another points. It should start off with 10T. You use other than 10T on two situations : (a) if 10T is less than 11 s than you should use 20T. (b) if oscillation dies off before reaching 10 oscillation, then use 5T BUT if using 5T, then you should have 5 repetitions rather than 3 repetitions.

And when come to measure the diameter of the tin can, many of you have forgotten the CORRECT way of useing the set-squares. It send shivers down my spine this time, not yours. I really hope that you can pull up your socks and real fast, time is running short.

But as one of you told me, JPA scholars are selected students, tahan lasak, sure to ride the weather. I hope so, really hope so, that all of you will still be in one piece at the end of two years course and I still can recognise you. Hope you still recognise who am I.

From now on, all of you will be very busy, don't even have time to say hello to me, let alone reading my post. I may have to rest this blog for a while.

Time Waits For No One

Without realizing it, it was more than a month ago since I last updated my post. Half of the semester has gone by and I have finished the Physics unit 4 and half of ujit 5 with you. Very soon,real soon, all of you will be singing "sayonara" to all of us and UCSI.

Honestly, I am not totally satisfied with the progress. While most of you still keep up the tempo, some of you started to show sign of slacking, or is it crumbling under the pressure ?

I will just do a quick revision on the waves.

A wave is a disturbance that moves. A progressive wave transfers energy from the source outwards along the direction of propagation. In stationary wave, no energy is transferred along the direction of propagation.

Interference pattern is formed when two waves emerge from two narrow slits. The two slits serve as coherent sources so that a constant interference pattern is observed. If the two sources are not coherent, then the pattern keeps on changing so fast that we observed no pattern. At any distance D from the double slits, the distance between two nodes or two antinodes is known as fringe width or fringe separation x.
The relationship is given by :-

wavelength = slits separation (a) X fringe width (x) / D

If one of the slits is covered, then the pattern will change to diffraction pattern of a single slit, comprising dark and bright fringes of unequal intensity and width (unlike the double slit interference pattern which is of equal width and almost equal intensities).

Then there is diffraction images formed when light passes through an diffraction gratings. Gratings is a piece of hard plastics with handred of lines engraved per mm length. The images are formed with the zero order image at the centre flanked by images of first order, second order and so on on both sides of zero order image. Again, the images are not evenly spaced and intensity diminished from the highest in the zero order. You have to remember the relationship between the wavelength of the incident ray and the angle of diffraction of various order wavefronts.

wavelength = line separation x sin (angle of diffraction) / order

For standing wave to form, the two waves with same frequency and amplitude will travel in opposite direction with same speed. Or an incident waves met with the reflected waves from the opposite direction. Interference between incident and reflected wave will form a standing wave.

The distance between succesive nodes or antinodes = half wavelength.
For transverse waves, standing wave is formed with both ends ending with nodes.

Simplest standing wave => one closed loop___ Fundamental ____First harmonic

:::::::::::::::::::::::::::::::::::::::::two loops ______First overtone ____Second harmonic

::::::::::::::::::::::::::::::::::::::::three loops _____Second overtone ___Third harmonic

For longitudinal waves, standing wave is formed with one end node and the other antinode.

Simplest standing wave => Half loop ----------Fundamental --------First harmonic

::::::::::::::::::::::::::::one and a half loops -------first overtone --------Third harmonic

::::::::::::::::::::::::::::two and a half loops -------second overtone ------fifth harmonic

Lately, some of you didn't hand in the practical reports without any valid reason. I didn't say anything is not because I didn't notice that. Rather, I feel that I had said enough. If they choose to do what they did, I can't do much. Obviously I am in no position to help those who don't want to help themselves. I don't feel angry, rather, I feel sad for them. Luckily, they are onlythe minority.

Fundamental And Harmonics

In the section of the standing waves, there is some confusion over the fundamental and the harmonics with what I have written in the notes. Well,books are not uniform in naming the fundamental, harmonics or the overtones. To settle it once and for all, we will adopt the followings for standing waves :-

1 Loop

First Harmonic or Fundamental

2 l00ps

Second Harmonic or First Overtone

3 Loops

Third Harmonic or Second Overtone

## Please make the Neccessary adjustment ###

11.20 AM

Smiles All Round

It is the result time again. I heard laughters everywhere, the sounds of happiness. Many got their surprises in Physics. Many don't believe their eyes when they got their Physics results because they thought they are goner when they didn't get good results in their experiments. Now they should believe me that results of the experiment forms only part of the total marks. The other parts form the bulk of the marks. Hope you will learn the lessons and learn it well. Use the practicals to help you to do well in your unit 5. To learn from your experience is wisdom. If not, the experience is just another data entry. If you keep on repeating the same mistake, no one can help you.

Anyway,congratulations to all, this is the reward for your superb effort. Keep it up.

When Will I See You ?

A good answer to your PHY 5 Practical Test Question C is what I am waiting for.

After marking few papers and flipping through the rest, only 3 words that flash across my mind: they are not "ilu" but "omg" . I told myself I have to post this. There is no way to possiblly marking your papers without rewriting the whole answers in full.

To answer well in this section of unit 5 practical, you must think before you write, not write without knowing what is required of the question.

You must think in logical sequence. Think of

a) which variable should be kept constant :- in this case it is the length of string
b)what are the two variables you need to vary and investigate :- tension and frequencies
c)how to vary the variables.

A suggested answer to this section should be:

The length of string between vibrator and pulley is kept constant. For a fixed mass in the hanger, the frequency of the signal generator is varied until maximum amplitude of oscillation is observed. The frequency at resonance is recorded. The experiment is then repeated with the mass on the hanger varied and each time the resonance frequency is recorded.

Some of you forgot to change the mass to S.I. unit of kg.

On (b) (ii). should be

The graph is a straight line with positive gradient but it didn't pass through the origin. either

This is due to the systematic error,hence the graph could support the suggested equation. or

There is a constant term in the equation, hence the graph does not support the equation.

The experiment on Thursday,14th August will be June 2005 paper.

Tsunami That Never Came

It has been a long long while since I last wrote.

At the moment, the adult world is having the Pau contest. They are figuring who is to contest Mr Ang Wah for the title of the Pao master. In the miniature world of the 2007 JPA students, there is also a pairing exercise going on. The bees(ybodies) are busy figuring out which pot of honey belongs to which worker bee and forgotten that their job is to serve the queen bee. Some even want to claim not one but TWO pots of honey!! I say :-why not leaves the honey as pure, the mutiara as suci and the xy stays as variables. Is the activity the way of de-stress the stressful life of the JPA students ? Or .... ???

I started the extra classes in anticipation that the circular motion,vibration and the waves will set the fluid in your cochlea perpetual in motion and throw you off balance. The classes is to cushion off the tsunami effect of the waves. As the result,the number of students that came to see me dwindle and they are as happy as ever. Maybe the extra classes did the trick.

For some reasons I have to cancel the Tuesday extra class, so to balance off, I cancel the Monday class as well. There were joys around except one soft voice asking "why?" . It makes me wonder " Am I adding stress to them instead of reducing it?" It makes me Wonder...wonder.

Maybe I have taught them well that they have less doubts now (which I hope so) ; maybe they are more mature to seek out the answers themselves instead of relying only on me (which I will be very glad to know that) or maybe they are complacent thinking that they have the extra 2 hrs to cushion off and hope that it can be increased further.

Whatever it is, the benefit of doubts is always for the students,but sometimes it is beyond my control. Like the saying : Kita yang merancang, Tuhan yang menentukannya.

On the stationary waves 1st question, the electrons are assumed to be travelling like waves. This is called the duality of wave - particle which we will discuss in quantum Physics. It outlines that there is a wave property in particle (like diffraction) and a particle characteristic in wave (like momentum). So in this question, we will answer that motion of electrons act as standing waves in the orbit, as such, there are always complete number of waves in each orbit. In higher orbit, higher number of waves will be formed so that their frequencies are higher. The energy level of each atom is discrete.

Till then.