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.