Measure the Speed of Light using a Chocolate Bar

Step 1. check the Shopping List:

This is a very short shopping list for a super-cool activity that is used in college-level physics labs!

• A large 1 lb. bar of chocolate (I use Hershey's, but any kind should do)
• A ruler, pencil and paper
• A microwave oven and a plate

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Step 2. Do the activity yourself:

Measure the Speed of Light using a Chocolate Bar

When you warm up leftovers, have you ever wondered why the microwave heats the food and not the plate? (Well, some plates, anyway.) It has to do with the way microwave ovens work.
Microwave ovens use dielectric heating (or high frequency heating) to heat your food. Basically, the microwave oven shoots light beams that are tuned to excite the water molecule. Foods that contain water will step up a notch in energy levels as heat. (The microwave radiation can also excite other polarized molecules in addition to the water molecule, which is why some plates also get hot.)

One of the biggest challenges with measuring the speed of light is light travels really fast… too fast to watch with our eyeballs.  So instead, we're going to watch the effects of microwave light and base our measurements on the effects the light has on different kinds of food.  What's really cool about this experiment that you can see the size of the wave for yourself by measuring the burn marks in the chocolate. Microwaves use light with a wavelength of 0.01 to 10 cm (that's the size of the wave itself).

Key Concepts

Energy can take one of two forms: matter and light (called electromagnetic radiation). Matter is what stuff is made from, like a chair or a table, and we'll talk a lot more about matter when we get to chemistry.
Light is energy that can travel through space and through some kinds of matter, like glass. Another word for light is “electromagnetic radiation”. Light can have high energy, lower energy, or anything in between… kind of like high energy kids (the ones who race all over the playground), lower energy kids (the ones reading a book in a corner), and kids whose energy is somewhere in the middle.
Scientists usually refer to the light energy you can see with your eyes as “visible light”, or just “light”, and it has middle-of-the-road amounts of energy – not high, not low. Just average. That kind of electromagnetic radiation is called “light”.

Lower energy electromagnetic radiation can have wavelengths longer than a football field, and those are called “radio waves”. These aren't the kind of waves that a guitar string makes when you pluck it. Radio waves are not sound waves. They are waves made out of electricity and magnetism (which we'll discuss later) that travel through space. Sound waves need something, like air, in order to travel because it does it by vibrating molecules. Electromagnetic waves work differently, but it's a little more complicated than we're going to discuss now, so just remember that light waves are different than sound waves. If you've ever seen a lightning storm, you know this is true, because you see the lightning way before you hear the thunder. Which wave do you think travels faster? Light or sound? Other examples of lower energy waves are the kind found in your microwave oven called “microwaves” (surprised?) Your TV remote uses infra-red electromagnetic radiation, which has a little more energy than microwaves. What about high energy waves? If you've ever been curious about why the dentist puts a heavy lead apron on you before x-raying your teeth, it's because they're about to use high-energy electromagnetic radiation called “x-rays” to see through your mouth tissues to get to the bones and teeth. Since high-energy rays can destroy living tissue, you have to wear that apron. Lead stops most high-energy electromagnetic radiation in the x-ray range. Black holes, supernovae, and quasars in the deep reaches of space emit deadly x-rays and even higher-energy gamma rays.

Experiment 

Video  http://www.superchargedscience.com/lnc813-16.htm

Materials:

• chocolate bar (extra-large bars work best)
• microwave
• plate
• ruler
• calculator
• pencil and paper

 

1. First, you'll need to find the ‘hot spots' in your microwave. 
2. Remove the turntable from your microwave and place a naked bar of chocolate on a plate inside the microwave. 
3. Make sure the chocolate bar is the BIG size – you'll need at least 7 inches of chocolate for this to work.
4. Turn the microwave on and wait a few minutes until you see small parts of the chocolate bar start to bubble up, and then quickly open the door (it will start to smoke if you leave it in too long). 
5. Look carefully at the chocolate bar without touching the surface… you are looking for TWO hotspots, not just one – they will look like small volcano eruptions on the surface of the bar.  If you don't have two, grab a fresh plate (you can reuse the chocolate bar) and try again, changing the location of the place inside the microwave. 
6. You're looking for the place where the microwave light hits the chocolate bar in two spots so you can measure the distance between the spots. Those places are the places where the microwave light wave hits the chocolate.
7. Open up the door or look on the back of your microwave for the technical specifications.  You're looking for a frequency in the 2,000-3,000 MHz range, usually about 2450 MHz. 
8. Write this number down on a sheet of paper – this tells you the microwave radiation frequency that the oven produces, and will be used for calculating the speed of light. (Be sure to run your experiment a few times before taking actual data, to be sure you've got everything running smoothly.  Have someone snap a photo of you getting ready to test, just for fun!)

Going further: You can experiment with other easy-to-melt foods, like cheese, buttered bread, chocolate chips, peanut butter, or marshmallows! Just pop in the first food type on a plate (without the turntable!) into the best spot in the microwave, and turn it on.  Remove when both hotspots form, and being careful not to touch the surface of the food, measure the center-to-center distance using your ruler in centimeters.
TIP: If you're using mini-marshmallows or chocolate chips (or other smaller foods), you'll need to spread them out in an even layer on your plate so you don't miss a spot that could be your hotspot!

How to Calculate the Speed of Light from your Data

Note that when you measure the distance between the hotspots, you are only measuring the peak-to-peak distance of the wave, which means you're only measuring half of the wave.  We'll multiply this number by two to get the actual length of the wave (wavelength).  If you're using centimeters, you'll also need to convert those to meters by dividing by 100.
So, if you measure 6.2 cm between your hotspots, and you want to calculate the speed of light and compare to the published value which is in meters per second, here's what you do:

2,450 MHz is really 2,450,000,000 Hz or 2,450,000,000 cycles per 1 second

Find the length of the wave (in cm):

2 * 6.2 cm = (12.4 cm) /(100 cm/m) = 0.124 meters

Multiply the wavelength by the microwave oven frequency:

0.124 m * 2,450,000,000 Hz = 303,800,000 m/s

The real (published) value for light speed is 299,792,458 m/s = 186,000 miles/second = 671,000,000 mph. How did you do?

Questions to Ask

1. What would happen if you used cheese instead of chocolate?
   
2. Does it matter where in the microwave the chocolate is located? Does placement of the chocolate affect the wavelength?
   
3. Can you explain what the burn marks on the chocolate bar are from?
   

BIg Chem; Big Harm? (NYT)

Son, this is one reason I have worked so hard to find a place to shop that doesn't have ANY harmful chemicals in their products.  You know my favorite store.  You may also want to click here after reading this article. ;-) This is an important science lesson.The assignment details follow the article.

BIG CHEM; BIG HARM?

by Nicolas Kristof

                                                                  edited by Mom

NEW research is demonstrating that some common chemicals all around us may be even more harmful than previously thought. It seems that they may damage us in ways that are transmitted generation after generation, imperiling not only us but also our descendants.

Yet following the script of Big Tobacco a generation ago, Big Chem has, so far, blocked any serious regulation of these endocrine disruptors, so called because they play havoc with hormones in the body’s endocrine system. 

One of the most common and alarming is bisphenol-A, better known as BPA. The failure to regulate it means that it is unavoidable. BPA is found in everything from plastics to canned food to A.T.M. receipts. More than 90 percent of Americans have it in their urine. 

Even before the latest research showing multigeneration effects, studies had linked BPA to breast cancer and diabetes, as well as to hyperactivity, aggression and depression in children.

Maybe it seems surprising to read a newspaper column about chemical safety because this isn’t an issue in the presidential campaign or even firmly on the national agenda. It’s not the kind of thing that we in the news media cover much. 

Yet the evidence is growing that these are significant threats of a kind that Washington continually fails to protect Americans from. The challenge is that they involve complex science and considerable uncertainty, and the chemical companies — like the tobacco companies before them — create financial incentives to encourage politicians to sit on the fence. So nothing happens. 

Yet although industry has, so far, been able to block broad national curbs on BPA, new findings on transgenerational effects may finally put a dent in Big Chem’s lobbying efforts. 

One good sign: In late July, a Senate committee, for the first, time passed the Safe Chemicals Act, landmark legislation sponsored by Senator Frank Lautenberg, a New Jersey Democrat, that would begin to regulate the safety of chemicals. 

Evidence of transgenerational effects of endocrine disruptors has been growing for a half-dozen years, but it mostly involved higher doses than humans would typically encounter.

Now Endocrinology, a peer-reviewed journal, has published a study measuring the impact of low doses of BPA. The study is devastating for the chemical industry.

THE EXPERIMENT:
Pregnant mice were exposed to BPA at dosages analogous to those humans typically receive. 

WHAT HAPPENED:
1) The offspring were less sociable than control mice (using metrics often used to assess an aspect of autism in humans), and various effects were also evident for the next three generations of mice. 

WHY?

The BPA seemed to interfere with the way the animals processed hormones like oxytocin and vasopressin, which affect trust and warm feelings. And while mice are not humans, research on mouse behavior is a standard way to evaluate new drugs or to measure the impact of chemicals. 

CLARIFICATION & COMMENTS by authors of the report

“It’s scary,” said Jennifer T. Wolstenholme, a postdoctoral fellow at the University of Virginia and the lead author of the report. She said that the researchers found behaviors in BPA-exposed mice and their descendants that may parallel autism spectrum disorder or attention deficit disorder in humans. 

Emilie Rissman, a co-author who is professor of biochemistry and molecular genetics at University of Virginia Medical School, noted that BPA doesn’t cause mutations in DNA. Rather, the impact is “epigenetic” — one of the hot concepts in biology these days — meaning that changes are transmitted not in DNA but by affecting the way genes are turned on and off.  These results at low doses add profoundly to concerns about endocrine disruptors,” said John Peterson Myers, chief scientist at Environmental Health Sciences. “It’s going to be harder than just eliminating exposure to one generation.” 

SCIENCE HISTORY NOTE:  In effect, this (epigenetic impact) is a bit like evolution through transmission of acquired characteristics — the theory of Jean-Baptiste Lamarck, the 19th-century scientist whom high school science classes make fun of as a foil to Charles Darwin. In epigenetics, Lamarck lives. 

The National Institutes of Health is concerned enough that it expects to make transgenerational impacts of endocrine disruptors a priority for research funding, according to a spokeswoman, Robin Mackar.

In his conclusion, the author of this New York Times Article offers his two cents:

Like a lot of Americans, I used to be skeptical of risks from chemicals like endocrine disruptors that are all around us. What could be safer than canned food? I figured that opposition came from tree-hugging Luddites prone to conspiracy theories.

Yet, a few years ago, I began to read the peer-reviewed journal articles, and it became obvious that the opposition to endocrine disruptors is led by toxicologists, endocrinologists, urologists and pediatricians. These are serious scientists, yet they don’t often have the ear of politicians or journalists.

I’m hoping these new studies can help vault the issue onto the national stage. Threats to us need to be addressed, even if they come not from Iranian nuclear weapons, but from things as banal as canned soup and A.T.M. receipts.

ORIGINAL SOURCE:
New York Times Article - Big Chem; Big Harm?
by NICHOLAS D. KRISTOF
Published: August 25, 2012

ASSIGNMENT:  
1) Read this New York Times article. Read a second time and take key word notes
I have edited with notes in red to keep you focused on important points.
2) VOCABULARY: Define and memorize the 20 bolded words or terms.  You already know many of the words and numerous other words can defined contextually.
3) Make sure you understand and memorize the 2 bolded sentences.
4) Become familiar enough with the article that you are ready to discuss it.
5)  Complete a re-write in your own words by Monday.
5) We can discuss this after dinner tonight.  :-)


Also see: http://kristof.blogs.nytimes.com/
 

Franklin Bell & Leyden Jar

Franklin bells are an early demonstration of electric charge designed to work with a *Leyden jar. They were invented by Benjamin Franklin in the 18th century during his experimentation with electricity. Franklin bells are only a qualitative indicator of electric charge and were used for simple demonstrations rather than research.

The bells consist of a metal stand with a crossbar, from which hang three bells. The outer two bells hang from conductive metal chains, while the central bell hangs from a nonconductive thread. In the spaces between these bells hang two metal clappers, small pendulums, which hang from nonconductive threads. A short metal chain hangs from the central bell.

The central bell's chain is put in contact with the inner surface of a * Leyden jar, while the outside surface of the jar is put in contact with the metal stand. The central bell takes its charge from the inner surface of the jar, while the outer surface charges the two bells on the conductive chains; this causes the bells to have a potential difference equal to that between the inner and outer surfaces of the jar. The hanging metal clappers will be attracted to one bell, will touch it, pick up its charge, and be repelled; they will then swing across to the other bell, and do the same there. Each time the clappers touch a bell, charge is transferred between the inner and outer surfaces of the *Leyden jar. When the jar is completely discharged, the bells will stop ringing.

Electric Fly Swatter + Coke Can = Franklin's Bell 

http://www.youtube.com/watch?v=jIL0ze6_GIY&feature=related 


What is a Leyden Jar?

A Leyden jar, or Leiden jar, is a device that "stores" static electricity between two electrodes on the inside and outside of a glass jar. It was the original form of the capacitor.

It was invented independently by German cleric Ewald Georg von Kleist on 11 October 1745 and by Dutch scientist Pieter van Musschenbroek of Leiden (Leyden) in 1745–1746.^[1] The invention was named for this city.

The Leyden jar was used to conduct many early experiments in electricity, and its discovery was of fundamental importance in the study of electricity. Previously, researchers had to resort to insulated conductors of large dimensions to store a charge. The Leyden jar provided a much more compact alternative.