What is the difference between an electric and a magnetic field?

What is the difference between an electric and a magnetic field?

An electric field exerts forces on electric charges while a magnetic field exerts forces on magnetic poles. If you place a positive electric charge in an upward-pointing electric field, that electric charge will accelerate upward (in the direction of the electric field). But if you place a stationary north magnetic pole (if you could find one) in that same electric field, nothing will happen. An electric field exerts no force on a stationary magnetic pole. On the other hand, if you place a north magnetic pole in an upward-pointing magnetic field, that pole will accelerate upward (in the direction of the magnetic field). But if you place a stationary positive electric charge in that same magnetic field, nothing will happen. So electric fields act on stationary electric charges and magnetic fields act on stationary magnetic poles.

When a station transmits a signal, do all receiving antennae have the same recip…

When a station transmits a signal, do all receiving antennae have the same reciprocal charge?

Yes. The transmitting antenna pushes huge amounts of charge up and down so that all of the receiving antennae respond primarily to it rather than to one another. However when many receiving antennae are very near one another, they can begin to cause trouble. In effect, each antenna draws a small amount of energy out of the radio wave. If there are too many nearby antennas, they will sap the radio wave’s energy and each receiving antenna will get less than its normal amount. The other way to look at this effect is to realize that the receiving antennas actually retransmit the radio wave that they receive, but upside down. They weaken the wave as a result. If there are too many antennas around, they will reduce the wave to almost nothing.

Where does the charge on the antenna come from?

Where does the charge on the antenna come from?

In the transmitting station, the moving charge is pumped back and forth between the ground and the antenna. The net charge in the vicinity of the station remains zero, but it is constantly being redistributed. Sometimes the antenna is positively charged and the ground is negatively charged and sometimes it’s the reverse. In the receiving station, the same may be true. But there are also hand-held receivers that do not touch the ground. In that case, the receiver is still neutral, but charge is being pushed back and forth along the antenna and tank so that when the antenna is positively charged, the bottom of the tank circuit itself is negatively charged.