# Do Photons Have Mass? Physics Forums FAQ

• Suraj Nehra
In summary, the conversation discusses the concept of photons not having mass and the application of De-Broglie's equation to determine the mass of a photon with a specific wavelength. The individual mentions an equation that is not applicable to photons and suggests using the correct equation, \lambda= \frac{h}{p}, to calculate the mass of a photon.
Suraj Nehra

But De-Broglie's equation says that wavelength=Plank constant / mass x velocity
i.e.
λ=h/mv

inserting values in the above relation we find the mass of a photon having certain wavelength

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Suraj Nehra said:
But De-Borgle's equation says that wavelength=Plank constant / mass x velocity
i.e.
λ=h/mv

inserting values in the above relation we find the mass of a photon having certain wavelength

You wrote the debroglie equation for a massive particle (where you can write its momentum as p=mv which is not correct for the photon). You should use instead $\lambda= \frac{h}{p}$.

Suraj Nehra

## 1. Do photons have mass?

No, photons do not have mass. They are considered to be massless particles according to the Standard Model of particle physics. This means that they do not have a rest mass, but they do have energy and momentum.

## 2. How can photons have energy and momentum without having mass?

According to Einstein's theory of relativity, mass and energy are equivalent. Photons are considered to be packets of energy, and their momentum is a result of their energy and the speed of light. Therefore, even though they do not have mass, they still have energy and momentum.

## 3. Can photons be affected by gravity?

Yes, photons can be affected by gravity. This is because gravity can bend the fabric of space-time, and photons travel through this fabric. Therefore, their path can be altered by the presence of a gravitational field, even though they do not have mass.

## 4. If photons do not have mass, how do they interact with matter?

Photons interact with matter through the electromagnetic force. They have an electric charge and can interact with charged particles in matter through electromagnetic interactions. This is how we can see, as photons interact with our eyes' cells and nerves, allowing us to perceive light.

## 5. Is it possible for photons to acquire mass?

Currently, there is no evidence or theory to suggest that photons can acquire mass. The Standard Model of particle physics, which has been extensively tested and confirmed, states that photons are massless particles. However, some theories propose the existence of particles called "photon-like" particles that could have mass, but they have not been observed or confirmed yet.

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