How does energy flow through the lava lamp?
As a class, in groups, we were asked to trace the energy flow through a lava lamp. We
then discussed these ideas, watched a video, and heard lectures about things relating to the
energy flow. Once again, we were asked to explain how we now thought about the process.
This paper will present by initial understanding, my current understanding, as well as ways in
which my understanding has been expanded.
First Response and Discussion: The electricity goes through the cord into the light. The
electricity then reaches the light, giving off light and heat energy. The heat, specifically, is then
transferred to the bottom of the glass, which in turn transfers the heat to the coil and wax. The
wax takes this heat and begins to turn it into mechanical energy, speeding up the atoms,
making it less dense and causing it to rise. At the top, heat energy is given off through the oil,
then glass, then to the air around the lamp. Once at the top of the lamp, the wax cools because
it is further away from the heat source. Once a certain amount of heat energy given off, the
wax atoms move less, becoming more solid and less dense. The wax begins to sink to the
bottom of the lamp to begin again.
My answer prior to our discussion was fairly accurate, I feel that I learned more during
other lessons than this one. We successfully traced the energy through the system and
explained what it did and why. I knew what radiation was as well as conduction, simply from
physics class a few years back. I understood the mechanics of convection and why it works. The
picture of something like wax going in a circular motion was something I did not have, as I
always pictured the convection process expanding the heated air to all over the place rather
than in a more circular, confined motion and area, though I understood that heated things go
up and then, when cool, come down to reheat. My fourth grade science class did this by all
standing in 2 lines on the stairs and pretending that we were heating up and cooling down and
moving up and down the stairs. However, I had never been effectively taught the term
“convection” to the point where I could remember what the process was called.
Second Response Discussion: The light produces light and heat from the electricity
transmitted through the cord. The heat is radiated, or moved through the atmosphere to affect
something not touching the source, from the light to the glass of the lamp. The glass begins to
warm up from this radiated heat. As it begins to warm up, the heat is passed to the coil through
conduction, when the lamp and coil are touching so the heat can be directly passed. The coil
and glass, in turn, conduct more heat to the wax. The wax begins to melt, an effect of the heat
causing particles in the wax to move faster, liquefying it. Due to this liquefying, the wax
becomes less dense and begins to move upward as is absorbs heat. As the wax moves, it begins
to conduct heat to the oil surrounding it, which then conducts heat to the glass of the lamp
near the top. As the wax moves upward, it continually loses this heat without absorbing any
more heat from the heat source, which is farther away. The wax peaks at the top, radiating
much of its heat to the oil and glass lamp, and not absorbing much more due to the heat source
being at the bottom. The molecules begin to solidify as they cool and the wax becomes denser.
The wax then sinks back down to the bottom of the lamp, losing heat, but also absorbing more
and more as it becomes closer to the heat source. The process starts over. This form of heat
transfer, a cycle where an object or material gains and loses heat, is called a convection current.
In this case, the wax rises and falls as it loses and gains heat energy, causing a current/cycle to
form. The heat that is transferred through conduction to the oil and glass is radiated from the
glass to the atmosphere around the lamp. This can be felt by placing the hand near the lamp.
I feel that, after discussion of this topic and activities, I have a better, more in depth idea
of the heat transfer process of convection. Before, I understood the idea, but not to the extent
that I do now. For example, I never pictured the idea of convection as a circle. I thought of it
more as a volcano, erupting hot things that will float all over the place and eventually cool and
fall back to earth. Some may fall back into the volcano, heating back up and being erupted
again. The wax in the confined space of the lamp showed me that convection is not always
catastrophic and all over the place. It can be very contained, like it was in the lamp, though it is
still not ‘orderly.’ I also thought of convection as pushing the heated thing far away from the
source of the heat, much like a volcano again, rather than just a short distance away as we saw
in our lamp. I had never ruled out that the thing being pushed in the current could stay
relatively close to the heat source, I just had never thought about it. These misconceptions may
have occurred because I had little prior knowledge of convection currents. The only example I
would have been able to give you was air or water.
With these new bits of knowledge, I feel that I have a pretty well rounded
understanding of the three ways heat is transferred. I know I could never explain it like a
professor of thermal dynamics, so there is always more that I can learn. However, I would feel
comfortable teaching a class on the different ways heat is transferred and where we see them
in life. I thought it was also really interesting to see, in the Bill Nye movie, that the more
molecules an object has, the more heat energy it contains. It makes sense, with the energy
contained in the molecules, but I had never thought about it this way. I would like to learn more
about that because I feel that is something I could not explain to a class.
As one can see, I thought I understood the heat transfer processes completely before
this lesson. However, I has a few misunderstandings of convection currents. These activities
helped me to expand my knowledge. By looking back on what I originally thought and how my
thinking has changed, I am shown once again how there is always something to be learned.