I can easily detect the presence of magnetic field over a surface by using compass or by placing some iron filings. But how could we similarly detect electric field over a place?
[Physics] How to detect an electric field
electric-fieldselectricityelectromagnetismmagnetic fields
Related Solutions
If them magnetic field is creating electric field and they combine to form EM waves, why does a compass show a magnetic field around the wire?
To produce EM waves, we do need the current to be time varying such that the magnetic field is time varying which induces a time varying electric field etc.
However, it isn't that case that the entire magnetic field produced by the time varying current is associated with EM radiation.
In the reactive near field close to the wire, there are time varying electric and magnetic fields that are not associated with EM waves (which transport energy away) but are, rather, associated with energy storage. From the linked article:
For example, current flowing in the antenna creates a purely magnetic component in the near-field, which then collapses as the antenna current begins to reverse, causing transfer of the field's magnetic energy back to electrons in the antenna as the changing magnetic field causes a self-inductive effect on the antenna that generated it. This returns energy to the antenna in a regenerative way, so that it is not lost.
This is all quite complicated in general but, for low frequency, e.g., 60Hz AC current along a wire in a circuit, the sinusoidally time varying magnetic field dominates.
Energy is alternately stored in this field (as the current magnitude increases) and returned (as the current magnitude decreases).
It's a fair question. A particle in a magnetic field becomes magnetized, and experiences two forces: a torque due to the face that its (induced) dipole moment is not aligned with the magnetic field, and a force due to the gradient of the magnetic field.
Now on a macroscopic level, the gradient is strongest near the poles of the magnet, and you will see a considerable quantity of filings pile up there; but as you get further from the poles, the gradient becomes very weak (roughly as the fourth power of the distance).
The induced dipole itself is proportional to the strength of the field, and the force is the product of dipole and gradient. This means that the gradient effect becomes much weaker with distance: for a bar magnet, field falls roughly with distance cubed (at sufficiently large distance), so gradient falls with fourth power and the attractive force with the seventh power of distance. By contrast, the torque that aligns the particles goes as the sixth power. That sounds really bad as well, until you realize that a metal filing will act as a local "field amplifier": it "pulls the field lines towards it", leading to a concentration of field lines at the tip - and a strong (but very localized) gradient. This gradient means that nearby filing particles will strongly attract each other, and align into the characteristic pattern you are familiar with. But there is no such amplification at a distance - so the particles won't move on a large scale, as there are no large scale gradients to push them.
Best Answer
If all you want is a visual demonstration of the electric field then you can use an electric compass needle which is the equivalent of a magnetic compass needle
as described here.
or you could use semolina (instead of iron filings) immersed in castor oil
as described here