bxbxb3 said:
Could anyone tell
me, if a capacitor is compared to a rubber sheet connected to a water
pump, what could be the possible analogy for an inductor. That example
was pretty good to compare and imagine. Thanks
An inductor is like a water pump without a motor, it is driven by the
water that is pushed through it.
It needs a pressure and a current to get going, and then it keeps on
running, pumping water, until the resistance slows down the current.
This is used in cars for creating a spark, or to create the starting
spark in a flouroscent tube.
Voltage is used to get the current running in a coil, and then suddenly
the connection is cut off, the current still pumps through the coil and
where is that current going to go? It has nowhere to go so the voltage
increases until a spark jumps over to ground, and that spark starts the
car or the fluoroscent tube.
Inductors have a resistance against quick changes in the current,
capacitors have a resistance against quick changes in the voltage.
The resistance changes with frequency, so inductors have little
resistance at low frequencies and high resistance at high frequencies.
There is a diagram over these factors which I think is very useful but I
can only find it in a pdf file from a swedish company.
http://www.elfa.se/se/fakta.pdf
This pdf is written in swedish but that doesn't matter because it is
only the diagram we need. In the index find the word " Induktanser" and
click on it, then scroll down one page, there is the diagram. Zoom in to
see the details. It is on page 33 in the pdf file.
You can see how the horizontal scale is the frequency scale, the vertical
scale is resistance, diagonally you see inductance and capacitance.
This diagram tells you what resistance a certain inductance or
capacitance has at a certain frequency.
For example, we want to know what inductor is needed for a loudspeaker
filter, it should have a resistance of 10 Ohms at 200Hz.
We go into the diagram from the horisontal 10 Ohm line, follow it to the
(vertical) 200Hz line, there is our working point. From there, follow the
diagonal line down left towards the border of the diagram and you see the
value 10uH.
So, we need a 10uH coil for this purpose.
I wish there was a better way to find such a diagram, better than to have
to download a pdf file in swedish and find the diagram. If anybody knows
about such diagrams in other places on the web, tell us about it.
These diagrams are useful because you only need your eyes to focus and
follow lines, there is no need to do calculations or touch anything, I
have this diagram in front of me all the time at the work bench, and use
it very often.