# Does Light Have Mass? Weight of Photon Explained

• dev70
In summary, the conversation discusses the possibility of light having mass and its potential effects when focused on a weighing machine in a vacuum chamber. The conclusion is that while light has momentum and can exert pressure on a scale, it does not have mass.
dev70
hi pf, my friends asked me a strange question to me today,
"if in a vacuum chamber if light is somehow focused on a suitable weighing machine then will there be any deflection?
if yes does that mean light has mass? "

sounds strange, isnt? that why i choose to ask here?

Focused in which way? Coming from above, reflecting light upwards? This will transfer momentum, and the scale will change.
Focused to have a high and constant energy density close to some (hypothetical) very sensitive scale? The scale should see an attraction.
Something else?

coming from above, and focused on a sensitive scale..

Light has a momentum, and momentum times intensity is a pressure. Pressure times surface area (of your scale, or focus) is a force, and the scale can measure this.
The Nichols radiometer is not a scale, but it operates with light pressure.

wow..beautiful explanation. i think i got it... i need some time for review..thanks by the way

i guess it doesn't have anything to do with mass of photon?

A photon has no mass.

## 1. Does light have mass?

No, light does not have mass. It is composed of massless particles called photons.

## 2. If light doesn't have mass, why does it have weight?

Weight is a measure of the force of gravity acting on an object's mass. Since light has no mass, it does not experience the force of gravity and therefore does not have weight.

## 3. Can light be affected by gravity?

Yes, even though light has no mass, it can still be affected by gravity. This is because gravity can bend the path of light as it travels through space. This phenomenon is known as gravitational lensing.

## 4. How can a photon have energy if it has no mass?

According to Einstein's famous equation E=mc^2, energy and mass are interchangeable. Since light has no mass, it must have energy in order to exist. The energy of a photon is directly proportional to its frequency, with higher frequency light having more energy.

## 5. Is it possible for light to gain mass?

No, it is not possible for light to gain mass. As mentioned earlier, light is composed of massless particles called photons. These particles cannot gain mass, as they are already massless.

Replies
19
Views
2K
Replies
4
Views
7K
Replies
14
Views
4K
Replies
19
Views
3K
Replies
6
Views
959
Replies
32
Views
2K
Replies
7
Views
4K
Replies
7
Views
2K
Replies
7
Views
2K
Replies
5
Views
2K