light WEIGHT. Does light have weight. Why?

[agbey]

Light is able to cause solar panels to generate energy. how is that? what causes the movement of electrons in the semiconducting materials?

 

[lisamoni]

solar panels are just like photo detector,a p-n junction on which when light falls than it absorbs energy and electron-hole pairs are generated in depletion region.than they are defused in p and n region and a voltage is generated across the p-n junction.if the circuit is closed and load is connected than current flows.this we use solar energy.u can understand from the book "optoelectronics and photons" by kasap.its helpful

 

[agbey]

thanks but does light have weight?

 

[mrflibble]

thanks but does light have weight?

As far as we know photons have zero rest mass. (Read: the experimental upper bound for the photon rest mass is very very tiny.)

Photons do carry momentum however...

 

[123jack]

On the other hand light can create pressure (see - solar sails).
Is pure energy sufficient to do so or is mass required?

jack

 

[bluehole]

E=h * nu h= planks constant \nu = frequency of wave
E=m * c^2 m = mass and c= velocity of light

equating these 2 equation
m*c^2=h * nu
m=h*nu/c^2
c is constant in a medium.
so h/c^2 is also constant assume it "kapa"
So mass of a photon m="kapa" * nu

Now put all the values and find out the rest mass of photon for a frequency.

 

[albbg]

You cannot derive the mass of the photons applying Planck's and Einstein's equation since it is applicable only to finite particles like protons, electrons, etc.
From Einstein's special relativity the rest mast of a photon must be zero.

Planck's equation give us the moving mass (not the rest mass) of the photon, in fact the total energy of the photon is:

E² = (p•c)² + (m•c²)²

p is the momentum, m the rest mass and c the velocity of the ligth.

Since m = 0 then the equation reduces to:

E = (p•c)

the momentum "p" depends linearly from the frequency, thus:

p = constant*ω

using a single constant "h" and the frequency "nu " we will have:

E = h•nu

But we derived it considering the rest mass to be zero.

 

[tpetar]

I think light have weight. A box of light weighs more than an empty box. The reason is that all forms of energy have weight (for now). Weight of light is insignificant compared to other weights.

I will ask another question does darkness have weight ? What with dark mattery in space which make darkness in space?

 

[eagledot]

Photons energy is calculated using their mass asfair (E=1/2*mv²). And they are bent by strong gravity fields, so they ought to have weight as well. Maybe this shows they include the yet to be proven "gravitron" subatomic particle.

 

[BradtheRad]

I think light have weight. A box of light weighs more than an empty box. The reason is that all forms of energy have weight (for now). Weight of light is insignificant compared to other weights.

I will ask another question does darkness have weight ? What with dark mattery in space which make darkness in space?

Yes. This is creative thought at work.

A cubic mile of space has countless trillions of photons traversing it all the time, coming from countless stars, from every direction. If it weighs even the tiniest incalculable amount, then trillions of cubic miles (light years!) of space adds up to a lot of weight.

My theory is that this is the missing dark matter which astrophysicists calculate is 80 percent of the universe.

And even if photons are absolutely weightless, they may 'mimic' mass as they move at the speed of light. After all, doesn't the theory of relativity state that mass increases to infinity at lightspeed?