E =mc2. e = hf is it different?

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E=mc² and E=hf serve different purposes in physics, with E=mc² relating to the energy content of mass and E=hf focusing on the energy of photons based on their frequency. E=mc² is applicable to massive particles, while E=hf is specifically for photons, where f represents frequency. The relationship between mass and energy is further expanded in the equation E²=M²c⁴+P²c², which incorporates momentum. For photons, which have zero rest mass, the relevant equation simplifies to E=Pc. Both equations can be correct depending on whether mass is considered as rest mass or relativistic mass.
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e =mc2. e = hf

is it different?
than why??

..e =mc2 this only use in nuclear??
 
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E=mc^2 is the rest mass of a massive particle.
That other thing over there is the energy of a photon.
 
If you put the two together and write f=c/λ then you can rearrange
mc2 = hc/λ to give λ = h/mc
DeBroglie did precisely this to come up with his hypothesis that λ = h/momentum
Which is the basis of wave - particle duality
 
The equation E=MC2 is used to find the energy content of some amount of mass. (Rest mass/invariant mass)

The equation E=hf is used to find the energy content a photon, where f = frequency of the photon.

Note that E=MC2 is actually part of a larger equation: E2=M2C4+P2C2, where P = momentum of the object. This allows you to find the energy content of an object based on its mass AND its motion relative to yourself.
 
as Emilyjoint is saying, if we take 'm' to be the 'relativistic mass', then e =mc2 and e = hf are both correct for a photon.

But as Drakkith is saying, if we take 'm' to be the 'rest mass', then the full equation is E2=M2C4+P2C2 and for a photon, the rest mass is zero, so E=PC for a photon.
 

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