When we switch on the TV, the sound appears first rather than picture.Why?

Answer 1

It has nothing to do with the speed of sound or the speed of light. Until the sound or picture actually leave the TV, both signals move at the speed of electricity. The exact speed depends on the electrical components making up your electronic circuit, so the two signals may be moving at different speeds. Regardless, both signals move through their respective circuit fast enough you would never be able to perceive the difference.

The reason for the delay is that the picture tube is a cathode ray tube. It uses an electron gun, which shoots electrons at the screen on the front of the TV. The way it shoots these electrons is to heat up the cathode until electrons are released. The electrons are sped up in the general direction of the screen by electrodes at the other end of the gun and aimed at the appropriate spot on the TV by electromagnetic fields.

The delay in the picture is because of the time required for the cathode to get hot enough to begin emitting electrons.

Edit: If the idea of an electron gun shooting electrons at the front of the screen makes you nervous, you're not alone. In the early days of TV, lots of moms persistently told their kids not to sit so close to the TV for fear of damaging their kids' eyes. Actually, the electrons never pass through the phosphorent screen. The main hazard associated with color TVs are related to the small amount of X-rays emitted when fast moving electrons hit the screen (black and white TVs don't shoot electrons fast enough to produce X-rays). These are blocked by leaded glass, but the leaded glass itself is toxic should you somehow break your picture tube. The leaded glass is also one of the reasons disposing of old TVs and computer monitors in landfills are a bad idea.

Answer 2

If you have a CRT based TV it takes time for the filament of the electron gun to warm up (the high voltages are present almost instantly), so there are no electrons to make a pciture. But the sound just depends on the electronics.

If you have and LCD or Plasma TV, there is no real time lag (some older models have a time lag because there is more digital processing to do on the video signal to put it on screen, but newer models do not suffer from this).

Answer 3

It takes some time for the picture tube in TV sets of that type to warm up (a few seconds on some; maybe ten seconds or more on older ones).

A cathode ray tube TV (as opposed to one with plasma or LCD technology) utilizes electron guns (which draw the image lines on the phosphor screen). These electron guns contain a filament heating element, which needs to literally warm up to do its job.

The audio circuitry doesn't require that kind of time; it merely needs an electrical currrent and it's good to go.

Answer 4

Sound signals do not require any processing.
Picture signals have to be read and then the TV tell the Cathode Ray Emitter where to point which point and the points glows in succussion so fast that they appear as a moving image.

Answer 5

I agree . A high voltage has to be developed across the CRT to accelerate the electrons towards the screen.
That takes a little bit time.

However, thereis no such constraint on speakers, and they can start playing the moment power is turned on.

Answer 6

speakers get the signals immediately and let them out simultaneously.

but in case of the picture tube the electron first heat the tube and when it is heated up to the visible scale the the picture becomes visible and slowly becomes more bright and reaches its full efficiency after about 15-30 Seconds.

Answer 7

It takes time to make the electrons move from the electrongun.But the sound is more efficiently amplified and boosted out.

Answer 8

Audio needs very little "Reassembly" compared to Video,this takes
a little more time.

Answer 9

I want to know too, I thought light is faster than sound.