王心凌 -- 月光

月光是王心凌的歌。 它是很美丽的歌。 but if we are talking about physics and science, there is a slight inaccuracy in that video clip of the song. if we move to minute 3:15 (plus minus several seconds), we can see there the moon is in its crescent shape.

as we all know, the moon is spherical. or if we see it in a 2-dimentional view it is circular. during full moon, the moon will look like perfect circular, reflecting the sun light to the earth. but during its crescent shape, the moon looks like ... erm, a crescent of cos, 哈哈 (how to describe the shape =P). it is like less than half circular. it becomes like dat bcos the other part of it is being blocked by the earth. so what we see on the moon of its "dark side" is actually earth's shadow.

so basically the moon still in round shape, but we see only the crescent part of it being lighted up by the sun. the rest should be black in shadow. but in that 王心凌 -- 月光 song, the dark side of the moon seems like dissapearing, showing that the moon is only within that crescent shape, and let the clouds behind the suppose-to-be-shadow of the moon, appears!! this is actually one of the misconception in depicting moon's image to the people.

similar analogy would be having a blasting sound if there is any explotion occur in outer space, which actually it will never happen. outer space is basically vacuum with no air at all. sound needs medium to travel to be heard by us.

Black Out

today is another day to continue my final year project. im doing it in digital signal processing lab. i was going to see the graph across a power resistor whose electricity source i plug in straight away to the outlet.

im trying to use the oscilloscope to see the sinusoidal voltage graph, hopping to see any harmonic introduced by that power resistor. from the oscilloscope prob, i put the measurement prob at one end of the resistor and the ground prob at the other end. i hoped dat grounding would give the zero voltage reference so that it can produce a nice 240 V rms sinusoidal voltage. but everytime i turn on the electricity source to the power resistor, suddenly ... blup!!


black out. suddenly there is no electricity coming out from the outlet. i could see from my laptop which is running using its battery (during any electricity source absence). luckily it was a localized blackout, so the lamps in my lab still on. i try to reset the tripped earth leakage circuit breaker (elcb) from the distribution board (db).

then the electricity is on again. but the same thing happen again every time i try to redo my experiment. only until the 5th attempt, i realize that the grounding prob from the oscilliscope is basically a true ground! haha ... of cos it cause black out. luckily the elcb is a trully good first-qually of circuit breaker. it trips really fast, or else i will be blame bcos of any damage in the lab equipments.

after i took out the ground probe and use only the measurement prob (without any reference now), only i can see the sinusoidal graph nicely in the oscilloscope. it really works perfectly showing at 240 V rms voltage value although without the ground prob. oh, this is something new for me to learn again. too bad there are too much harmonics in the voltage graph, i think it is all bcos of the power resistor.