If light has energy and we use E=mc^2 then how can light have no mass.?

Answer 1

The formula E=mc^2 is only the equivalent energy of a mass at rest. The full version is
E^2=m^2c^4 +p^2c^2.
This works for masses in motion as well as light. In this equation, m is the rest mass, p is the momentum, E is the total energy and c is the speed of light. For light, m=0 and we get E=pc. For a mass at rest, p=0 and E=mc^2.

Answer 2

In classical Physics we considered as mass as an independent quantity and mass is conserved.

When it is found that the speed of light is independent of the speed of the observer, the concept of mass has changed.

In classical Physics, a mass which is at rest is not having any energy; but now we say mass is the internal energy of the body and the internal energy of the body increases with its speed. Formerly a mass can be increased only by an addition of mass and nothing else.

But now we know, simply by increasing its speed, the mass of a body is increased. We are not adding any mass to it; however its mass increases.

Thus the unit of mass is no more the unit of mass alone; it can be thought of unit of energy also. The conversion of kilogram into joule is given by the equation E = m cc.
Or 1 kilogram = 9 x 10^16 joule.

If a mass is moving with a speed ‘v’, we have given it some energy. But the energy it was possessing when it was rest was m0 cc. The final energy is m cc. The difference in energy m cc - (mo) cc or (m - mo) cc is the energy of motion.

Thus in the equation E = M cc, The M should be understood as (m - mo).

If mo = zero, then M = m, which fits well for a photon whose rest mass is zero.

Answer 3

Light, or electromagnetic energy, is composed of waves that have different energy levels. Weal signals are like those found in radio waves. Strong signals are those that have frequencies in the cosmic range. The closer the frequency lines are in a given distance, the greater is the energy of that wave.

This form of energy is able to directly become "mass" as when a high frequency wave enters near the core of an atom and converts into negative and positive electrons. In this sense it is able to be seen that there is a direct relationship with light energy and mass.

Light has no direct mass value in that the definition of mass does not fit it when in that state - "offers resistance to movement". It does this when formed into he electron, but not it its free state.

Answer 4

*Chuckles* This is where things get really weird. The light photons are both particles having mass, AND energy waves at the same time.

Now it gets to the wierd part. The particles can go back in time, and the particles KNOW what YOUR doing- that is, they know before YOU do what you're looking for.

Theres a book called "In Search of Schrodingers Cat"- read it. Then read it again. Then if thats not weird enough for you, read "Godel, Ester, Bach- an Eternal Golden Triangle" and that will totally twist your understanding of the universe.

Good Luck

Answer 5

Light has no rest mass, meaning that it can only travel at the speed of light, not at a slower speed. But a photon travelling through space at the speed of light has mass equal to Planck's constant h times its frequency divided by the speed of light squared. Like any other moving mass it has momentum. It falls under gravity, so a beam of light passing close to a planet or star is bent slightly. But if you tried to slow it down, it would disappear.

Answer 6

Light is made up of Photons, which in current physics theory have a miniscule mass. That tiny amount of mass multiplied by the speed of light squared is still only a tiny amount of energy. Although this is a tiny amount of energy, millions of photons are involved. One of the proofs of this theory is Photvoltaic electric cells that power solar low voltage lights.

Answer 7

Light has mass in the name of " Photons "
Yes Photons have mass

Answer 8

Because the speed it's traveling at it can't contain a true mass. This is only a hypothosis but someone else may have the right answer.

Answer 9

Photons are practically massless. That's why we have a constant when we do our calculations called Planck's constant, usually referred to as h. Otherwise there would be an apparent paradox but with h we can get the math right!

Answer 10

Isn't zero greater than minus one.