Ludwik's example (below) is interesting. It depends upon what you mean
by "adding two things" together.
As stated, when viewing the light output with one battery, then the
other battery, then both batteries, the result falls into the category I
call synergism. The light output with both batteries is more than the
sum of the light outputs when each battery is used alone.
However, one might argue you're not really adding the two effects
together. To do that you would have two batteries and two lights. You
would measure the light from one battery-bulb combination (L1), then
measure the light from the second battery-bulb combination (L2), and
then measure the light with both bulbs lighted (LS = summed light). In
this case superposition would hold... L1 + L2 = LS.
I like this example because it is easy to describe and also easy to
demonstrate. However, if I were to use it in my teaching, I would be
inclined to demonstrate both cases. If I use Ludwik's example only, my
"less-bright" students might conclude combinations of light do not
follow the superposition principle.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu
Ludwik said...
Another example: two electric batteries, B1 and B2, in series with a
small light bulb. Each battery alone produces very small "amount of
light." But together they produce A which is much larger than A1+A2.
Most people have experience with flash light sources. They know that one
battery will produce much much less than 50% of light one gets from the
normal set of two batteries. Ludwik Kowalski