# Does electric and magnetic fields “Travel” or they just appear in space?

Suppose that we have a very, very large cubic box (with the edge much larger than the absolute value of $$c$$) which is completely empty. Now, suppose that we add in there a small sphere with some charge $$q$$ in one of the vertices. Will the electric field suddenly appear on the entirety of the box or it will "travel", expanding from the vertex at speed $$c$$? The same question applies to a magnetic field.

I thought about this while playing with some magnets. Suppose that, at the middle point of the box we have a wall, made of some material. If the magnetic field "travels", will the material change the intensity of the field on the other side? When i was playing with 2 magnets today, i noticed that both magnets would attract each other even when separated by a $$3\operatorname{cm}$$ thick block of wood. However, in a $$0.5 \operatorname{cm}$$ thick window glass, the magnets would not attract each other. To sum up, here are the two questions:

Does magnetic/electric field "travel" trough out space?

Does this imply that a material on the way might change the intensity of the field?

Thanks.

• "with the edge much larger than the absolute value of $c$" is a nonsensical statement because edge lengths are not measured in velocity units. – David Z Dec 21 '16 at 3:58
• That's why i said "absolute value". – embedded_dev Dec 21 '16 at 12:17
• That doesn't matter. Saying "absolute value" does nothing to address that problem. The absolute value of a velocity is still a velocity. – David Z Dec 21 '16 at 18:13
• I'm not an native english speaker. In my language when we say "absolute value" thats what we mean: the value, just the numeric value. Thank you for noticing it. I think i should have wrote "numerically bigger". – embedded_dev Dec 21 '16 at 23:37
• Ah, well the English terminology you want is "numeric value". For example, given a value of "-20 m/s", the numeric value is "-20", the unit is "m/s", and the absolute value is "20 m/s". In any case, none of these are valid measurements of an edge length, so the statement is still nonsensical. – David Z Dec 21 '16 at 23:43