I think it will be easier to answer your second
Electricity is really just
moving charges around. Either you can move
electrons around, or you can move other charged
particles around. It's all the same thing. When
you put salt in water, which as you might know is
made from one sodium ion (with a plus charge) and
one chloride ion (with a minus charge), the two
oppositely charged ions separate (why they do this
is an interesting story also!) So when you put
lots of salt in water, the charged ions from the
salt can move and allow electricity to conduct.
In fact, electricity does not conduct nearly as
well in water with absolutely no salt, but in fact
it is very hard to get water with absolutely no
ions in it.
Now, on to radio waves.
Radio,visible light, infrared, ultraviolet,
x-rays, microwaves and various other kinds of
waves turn out to all be the exact thing. The
only difference between them is the "wavelength"
of the wave. In any wave something moves back and
forth and the length of one complete cycle is
called the wavelength. It turns out that all of
these waves are able to move charges around - sort
of. The thing is that the radio and waves with
longer wavelengths move charges better than
visible light and x-rays. That's because the
shorter the wavelength, the faster the charges
have to move to keep up. And moving all those
charges around sucks up a lot of energy from the
So, in fact, the saltier the water,
the less able radio waves will be able to
penetrate through it. By the way, using the same
sort of reasoning you can explain why metals are
Anyway, the more you
understand about waves and their behaviors, the
more you can understand about the world around you.
Radio and other electromagnetic waves can travel
through liquids and solids. Having electromagnetic
(EM) waves travel through pure liquids usually
doesn't aid travel but it may not really hinder it
either (depending on what you mean by "hinder;" EM
waves traveling through a substance move more
slowly than EM waves traveling through vacuum).
Adding salt to water would, as you point out, have
the effect of increasing the electrical
conductivity of the liquid. This, actually, is
bad for transmitting a EM wave because the
increased conductivity will tend to disperse the
wave and attenuate the signal that gets
In sea water, radio waves don't
travel too far but microwaves might do better
because sea water isn't a "good" conductor any
more at those frequencies. On the other hand,
sounds waves travel through water very well so
submarines use sonar rather than radar.
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