# What does this sentence mean?

1. Jul 17, 2010

### ahmadicabara

A pure electric field in one reference frame is observed as a combination of both an electric field and a magnetic field in a moving reference frame. (from wikipedia)

Thank you

2. Jul 17, 2010

### Staff: Mentor

What do you think it means?

3. Jul 17, 2010

### Academic

It means that what looks to a 'stationary' observer as an electric field only looks to a moving observer as a combination of electric and magnetic fields. I guess I just restated exactly what it said lol What part of it dont you understand?

4. Jul 17, 2010

### ahmadicabara

I just don't get it. :d

5. Jul 17, 2010

### Academic

You need to be more specific than that, seriously dude. Do you understand what an electric field is? Do you understand what a frame of reference is? Do you understand what a magnetic field is?

If you observe an electric field in your frame of reference, somebody in a different frame of reference will observe both an electric field and a magnetic field.

6. Jul 17, 2010

### Staff: Mentor

Do you understand that a moving charge produces a magnetic field?

7. Jul 17, 2010

### ahmadicabara

Yes. The problem is that I wanted to relate this question to my initial question which was why a movin charge produces both B and E fields whole static charge produce only E field. Can someone help me?

8. Jul 17, 2010

### AJ Bentley

Does it help if I tell you that Electric and Magnetic fields are not two separate things but just different aspects of one thing (Sometimes we call it the Electromagnetic Field)?

What we call a Magnetic field is how this 'thing' appears to us when we are moving fast. What we call an Electric field is how it looks when we are standing still. If we only move slowly, it looks like a mixture of the two.

The 'thing' got two names because nobody realised at first it was the same.

9. Jul 17, 2010

### Staff: Mentor

Here's an example illustrating that electric and magnetic fields are two aspects of one thing, as special relativity has taught us: http://galileo.phys.virginia.edu/classes/252/rel_el_mag.html" [Broken]

Last edited by a moderator: May 4, 2017
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