# What are electromagnetic waves

Tags:
1. Feb 21, 2015

### Aafia

I am confusing about it that what are electromagnetic field books said that it does not require medium then how they propagate in vaccum and we also know that waves are disturbance through a medium

2. Feb 21, 2015

### Orodruin

Staff Emeritus
Electromagnetic waves are disturbances in the electromagnetic field. They do not require any medium to propagate in. Who has told you that waves are necessarily disturbances of a medium? Of course, there are such waves, but electromagnetic waves are not such waves.

3. Feb 21, 2015

### Aafia

can you explain how electric field produced in electromagnetic wave

Last edited: Feb 21, 2015
4. Feb 21, 2015

### Staff: Mentor

Atoms or electrons can be involved in producing EM fields, but they are not necessary. The behavior of EM fields is governed by Maxwell's equations, and Maxwell's equations have vacuum solutions, meaning that they can exist even without charges.

5. Feb 21, 2015

### Aafia

I read in my book that changing in electric field produce magnetic field which are perpendicular to each other and these fields are perpendicular to the propagation of waves ... sorry my english is not correct .. are you understanding my question

6. Feb 21, 2015

### Staff: Mentor

Yes, that is correct in a broad sense. There are, of course, some important details. Do you mind if I ask how much math background you have? Specifically, how much calculus do you know?

7. Feb 21, 2015

### Aafia

8. Feb 21, 2015

### Staff: Mentor

I would say that the electromagnetic field itself is the medium that they propagate in. When we talk about water waves propagating through water, we don't feel the need to invoke some other medium, do we?

9. Feb 21, 2015

### Aafia

Then can you explain briefly and easily what are they? To clear the concept abou EM waves :)

10. Feb 21, 2015

### Orodruin

Staff Emeritus
To some extent, yes. The reason I do not want to talk in that fashion (in particular with laymen) is that it risks creating a confusion, namely that there is something called "field" that is actually being displaced (as transversal or longitudinal displacement waves in a medium).

11. Feb 21, 2015

### Aafia

12. Feb 21, 2015

### Staff: Mentor

Do you know how to take derivatives or integrals? Are you familiar with differential equations, or vectors, or partial differential equations?

13. Feb 21, 2015

### Aafia

Yeah little bit know

14. Feb 21, 2015

### Staff: Mentor

OK, so electromagnetic fields are governed by Maxwell's equations:
http://en.wikipedia.org/wiki/Maxwell's_equations#Conventional_formulation_in_SI_units
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/maxeq.html#c3

If you do not have any charges or media (vacuum) then Maxwell's equations still apply, and in fact they simplify considerably:
http://en.wikipedia.org/wiki/Maxwel...s.2C_electromagnetic_waves_and_speed_of_light

Two of those simplified forms of Faraday's law and Ampere's law basically say that if a B field is changing in time then there is an E field which is changing (curl) in space, and vice versa. Putting those two together gives (with the help of some vector identities) the wave equation. Meaning that the E and B field together can form a wave in vacuum.

15. Feb 21, 2015