Sunday, April 26, 2009

MASS OF A PHOTON

Hi all..How can we measure the mass of a photon??

Is it possible to isolate a photon and put it in a closed box??

Photon has no rest mass. 
Although it's inertial or gravitational mass can be measured in this way - 

1. Take an empty box and apply a force on it, measure its acceleration. Obtain the mass of the box by diving the force applied by acceleration produced.

2. Take a single photon in the box now. Apply a force and measure its acceleration. Obtain the mass of the setup by dividing the force by acceleration.

3. Subtract the first mass from the second to get the inertial mass of a photon.

Although it is seemingly simple, it should be noted that no instrument can measure the inertial mass of a photon since it'll be very very small. And no instrument has such high accuracy.


Is it possible to isolate a photon and put it in a closed box??
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Yes, we can have an isolated photon. All you need to have is an excited atom. It will then emit a single photon.

And I remember reading somewhere that this has actually been done! 
It was done with excited potassium atoms ... but the experiment was different. It was done to challenge the wave-particle duality. 

Anyway, just goes to show that we CAN, even in actual practice have individual photons.

How will u measure the force appllied and acceleration produced??
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You don't need to measure force. Apply a known force.

And measure the velocities to find out the acceleration

a=v-u/t


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