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superposition



In presenting the superposition principle in electrostatics I decided
to invent an example in which the superposition principle does not
apply. This is pedagogically useful, I suppose. Here is the example I
will use.

Two heaters, H1 and H2, are located in a room. The temperature is
measured, for example, near a single-pane window. The absolute
temperature is T1 when H2 is off and after H1 has been on for a long
time. And the absolute temperature is T2 when H1 is off and after H2
has been on for a long time. Is it true that the temperature is T1+T2
after both heaters have been on for a long time? The answer is NO.

Many other examples of that kind can be invented, for example, magnetic
field near an iron core which has two independent coils. Each coil
(with a dc current) produces B but
the field is not 2*B when both coils are on at the same time, unless B
is verrrrry small.

Ludwik Kowalski