Chocolate bar in Microwave (Part-I)
Here’s a fun little experiment that anyone can conduct at home with a chocolate bar and a microwave oven.
Remove turntable from microwave (the plate that rotates)
Take a chocolate bar on a plate and place it inside microwave.
Heat for for 30-60 seconds on high.
You will notice that the chocolate would have melted in some regions and not in others (see image above). But don’t worry this is supposed to happen.
A microwave works by setting up a standing wave inside it.
The size of the oven is chosen so that the peaks and troughs of the reflected microwaves line up with the incoming waves and form a “standing wave”.
The above is a 1D analog of a standing wave, but a 2D standing wave looks like so:
And there are nodes and anti-notes in three dimensions throughout the entire oven.
At the anti-nodes is where the wave oscillates the most
And therefore a molecule placed at the anti-nodes will rub against each other more rigorously than the ones at the nodes.
More the rubbing, more the food the gets heated up.
This is why the chocolate in our image is melted in some regions (the anti-nodes) whether remains intact in others (the nodes).
If you take a ruler and measure the distance between two successive anti-nodes and plug it into the frequency-wavelength relationship, one can obtain the speed of light.
But the key insight that one can gather from this experiment is the visual feel for how long the wavelength of a microwave actually is!
It’s a lot of fun to do this experiment on your own.
So we encourage everyone to give it a shot. We will take a break here and we will dwell into more microwave physics in part-II.
