# Why light is not considered as a longitudinal wave?

1. Dec 16, 2013

### Trojan666ru

I would like see the reasons why light is not considered as a LWave

2. Dec 16, 2013

### Staff: Mentor

It can be polarized.

3. Dec 16, 2013

### Pythagorean

Because the quantity described in the amplitude of an electromagnetic wave is typically oriented perpendicular to the direction of propagation in physical space.

There are exceptions (like in plasmas), but that's a special circumstance.

4. Dec 17, 2013

### Trojan666ru

Nobody is clear in their answers.
I would like to hear the reasons
It can be polarised! What?

5. Dec 17, 2013

### Staff: Mentor

I don't know how much more clear I can be. Longitudinal waves cannot be polarized. Light can be polarized. Therefore light cannot be a longitudinal wave.

6. Dec 17, 2013

### Trojan666ru

How do we find that light can be polarized? Any experiment?

7. Dec 17, 2013

### Trojan666ru

Is that the only reason why light is considered as a traverse wave?

8. Dec 17, 2013

### Staff: Mentor

Pythagorean gave another reason, and there are most likely still other reasons. All the reasons are equivalent mathematically, but to me the polarization is the one that seems most clear.

9. Dec 17, 2013

### Staff: Mentor

Sure, take two polarizing filters (e.g. lenses from sunglasses), make light pass through both, and rotate them relative to each other to see light be blocked completely or pass.

10. Dec 20, 2013

### Claude Bile

Light can be polarised longitudinally! (e.g. in an optical fibre or other waveguide structure).

In a vacuum, however, Maxwell's equations dictate that light cannot have a longitudinally polarised component.

Claude.

11. Dec 20, 2013

### ZapperZ

Staff Emeritus
This is very confusing, and no one has asked the OP one very obvious question, so I will ask.

Trojan666ru: have you ever solved Maxwell equation to obtain the light's wave equation?