# Comparision of sound and light

Usually light travels faster than sound.However, when we switch a television set on,the picture comes later sound.What is the reason behind this : ?

## Replies

• Abhishek Rawal
In Television (considering it to be CRT TV) Cathode ray tube takes some time to properly heat, and once it is properly heated,it displays image on fluorescent screen.

Bit Off-topic :
You know,i had one TV which I was using for studies, it had one problem i.e Sound was obtained from the moment it is started but image appears after 2-3 hours, because CRT was taking very long in heating.
• lal
It is totally a different scenario. Sound and picture, are both transmitted as a electromagnetic wave from the transmitting station. Later, It is the television circuit which synthesises sound and picture in a TV. It depeneds on the circuit on which output comes first but not on the propagation speed of sound or light.

Edit:
Say you are watching a TV from quite a distance and the sound is pumped up enough to reach you. If the screen and speakers are both at same distance from you, you'll notice the conversations/voice lag!
• rahul69
N.SACHIN
Usually light travels faster than sound.However, when we switch a television set on,the picture comes later sound.What is the reason behind this : ?
We see lightning flash during lightning, before we hear thunder, and nature doesn't lie ðŸ˜‰
• Jeffrey Arulraj
Mate the relative time difference is really less

Sound takes 0.00303 s to travel a metre
At the same time light takes nearly a nano second to travel the same time

That can cause lag between both.

But in TV you don't notice lag as the video is also a sequence of images played rapidly for a few milli second. And this turn on and off time allows both the sound and light to sync with each other splendidly

The 25 frames per second allows us to watch and listen at the same time
• Ahsanul haque
The speed of light is 299,792,458 meters-per-second, which
is approximately 186,000 miles per second. This speed is usually same, no
matter about temperature or medium effect is travelling through it. But Sounds
speed is 32 miles per second. Lightning is a massive electrostatic discharge
between the electrically charged regions within clouds or between a cloud and
the Earth's surface. In Lighting Thunder Light we noticed it first after then
sound. After few mechanism then TV lights on.

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