2007-02-09 00:59:43 · 16 answers · asked by Anonymous in Science & Mathematics ➔ Physics
Sound is primarily a temporal variation in air pressure as sensed by the ear i.e., the change is over time. A still picture is a spatial variation in light intensity as percieved by the eye i.e., the change is over space. A "moving" picture is a temporal variation of a still picture. In a television set, the perception of a still picture (as when a photograph is being viewed on a TV screen) is created by a several pixels spread over the screen. When the eye is at a distance sufficent to fail resolving the individual pixels, the illusion of a continuous picture is resulted. When sufficient (usually 24 per second, the number being the maximum temporal resolution limit for the human eye) number of such still pictures are projected on the screen in quick succession, it is percieved as a "continuous" moving picture.
As such, the mechanism for reproducing sound is failrly simple - just make a rigid object vibrate as per the requirement and it can be easily achieved by electromagnetically vibrating a membrane by feeding electric signal in tune with the required notes/distribution of sound over time. Due to the inherent simplicity of this system, the audio start-up is almost instantaneous once the power is switched on.
The mechanism for reproducing a TV picture, however is fairly complex as from an electric signal, light intensities corresponding to the individual pixels on the screen need to be decoded, and then the different pixels need to be illuminated with their corresponding intensities to make the still picture. And there is more, this still picture needs to be refreshed once every 24 seconds with a new set of intensities so that the moving picture can be simulated. All this requires complex technologies and components/circuits. This complex system needs to "initialise" itself once the power is turned on, the bulk of time taken by the Cathode Ray Tube to "heat-up". More modern displays employ "solid-state" displays (like LCD) which take relatively less time to initialise, so it is quicker to start-up than conventional CRT screens.
Just to add, there IS spatial variation component in sound reproduction as well. This is for creating the "stereo" effect which is to create an illusion of spatial variation of sound as in real life. This technique employs multiple speakers, but no more than a few tens of speakers at most, compared to the number of visual display pixels which can number anywhere from hunderds of thousands to millions.
2007-02-12 07:14:15 · answer #1 · answered by lemmethink 2 · 0⤊ 0⤋
When u use a CRT(cathode ray tube) tv what happens is that there is a tube inside which radiates rays on the screen which we see. This tube takes a longer time to switch on then the sound that is why we hear the sound first. otherwise also the distance between u and the tv is so small that even if the light and sound started at the same time u could never tell the difference.
2007-02-09 22:06:43 · answer #2 · answered by The Pain 2 · 0⤊ 0⤋
The picture on the screen is due to an electron gun which fires electrons at a pretty fast rate. The reason that the sound is heard before seeing the picture is that the electron gun has to get charged first whereas the mechanism for producing the sound is totally different.
This is the reason why this phenomenon takes place only when we switch on the TV but after sometime it becomes alright
2007-02-09 09:06:49 · answer #3 · answered by vatsa 2 · 0⤊ 0⤋
This is because the sound leaves the TV first as it takes more power for the screen to start than it does the speakers.
2007-02-09 09:05:53 · answer #4 · answered by dazza 1 · 0⤊ 0⤋
The sound in a TV is coded by radio waves (which travel at the speed of light). There are no sound waves being picked up by a TV.
2007-02-09 09:04:37 · answer #5 · answered by mathematician 7 · 0⤊ 0⤋
The speaker will start to vibrate as soon as electricity hits it.
The picture tube requires a second or two to "warm up" and to collect enough power to light up.
The question has nothing to do with the speeds of light and sound.
2007-02-09 09:05:13 · answer #6 · answered by chocolahoma 7 · 0⤊ 0⤋
The sound and light do not start at the same time. The light source warms up as it is turned on and slowly starts to work, unlike the sound.
2007-02-09 09:04:21 · answer #7 · answered by bradiieee 2 · 1⤊ 0⤋
when we switch on the tv. the picture tube takes time to scatter the electrons onto the screen but the sound box is immediately activated..
2007-02-09 10:20:32 · answer #8 · answered by Mithil Arun 1 · 0⤊ 0⤋
yeh! ur right but think logically when u switch on ur TV it takes some seconds to start the picture tube and u can hear only sound first.
2007-02-09 11:16:53 · answer #9 · answered by Anonymous · 0⤊ 0⤋
It takes a little longer for the CRT, LCD, etc. to become active and create light than it does for the sound system's speaker to become active.
2007-02-09 09:06:32 · answer #10 · answered by Thinker 7 · 0⤊ 0⤋