for all those physicists,top contributers and answerers?

Question

if u place some water in a tray and turn on the sound of a speaker nearby,the water will start vibrating.

BUT if u replace the speakers with a torch light and flash it on the water,it'lll not vibrate........WHY?? both,light and sound,are waves.

if you're just gonna answer tht light acts a particle as well as wave,thn thnx alot! u can move on to another question without answering.
I need some xplanation on it

thnx a bajillion:)

Answer 1

Sound waves move the air which is in contact with the water and therefore moves the water.
Light waves are a variation in an electromagnetic field; water is not magnetic and therefore does not move in response to the variable magnetic field in the light beam or presence or absence of light.
The term 'wave' is used only to describe a type of variation in a field. The nature of the field is an entirely separate matter.

Answer 2

There's another reason for that: frequency. If you let a pendulum vibrate freely, it will have vibrate with a certain natural frequency (say one cycle per second). If you start pushing it with the same frequency (like applying a single push whenever it reaches a peak) the vibration will increase. However, if you apply a force at a very high frequency (5000 push per second), the pendulum will just have very small unnoticeable vibrations and will actually look like it's not moving. Sound waves have frequencies between 20 Hz to 2 KHz. Light has very high frequency. It looks like the natural frequency for the surface of water is close to the range of the sound coming out from the speaker.
So to get the water surface to move, you need to satisfy two things: The nature of the wave as discussed by the guys above and its frequency.

Answer 3

steve is basically right: sound waves are made up of particles (air molecules) that are actually moving; these particles push and pull on the surface of the water (they appear as pressure variations at the frequency of the wave). In light waves, no particle of matter is moving, only magnitude and direction of electric and magnetic fields. Only objects subject to being forced by these fields (namely, charges) will move under their influence.

Answer 4

The light waves are very very small as compared to the sound waves, for one thing. But light goes through water and doesn't use it as a medium for propogation like sound does - light is still light, even in water. Sound is not anything by itself but a vibration of whatever it's moving through - that's why the water moves.

Answer 5

Hi. The speakers will impart heat (atomic vibration) in the water just as a torch will. The torch causes local vibration as the water heats, but if the energy transferred to the water is equal then the end result is the same.

Answer 6

Think in terms of energy *levels.* Were you to apply a strong enough and highly concentrated light source in your scenario, the water would be thermally disturbed.

Answer 7

sorry dont know.