Physical Science: We started off talking about the last exam. Overall I was pretty happy with the results, and I think we will do okay in the future when we have to do measurements and make graphs. We also spent a bit of time talking about the Mythbusters video from yesterday and its relationship to the test question that referred to it. Having seen the video now, it was clear the differences in the Independent and Dependent Variables, even to kids who struggle with the concept.
Then to introduce them to our Chemistry units, I did a demo involving heavy gases. Basically I break my demos up into observations and then I let them throw in inferences while they formulate a hypothesis. This demo in particular has a flask of hexanes (5 drops in 50 ml E-Flask) that turns to vapor. I then pour this down an inclined track, which has a candle burning at the bottom. After a few seconds, a fire trail goes back up the ramp.
I like this demo for a few reasons. It draws out the ideas of states of matter, and lets us talk about those differences. In trying to figure out why the gas doesn’t escape the flask when I open it, and why it can be poured down the ramp, kids always say the gas is “heavier” or “more dense.” We then talk about what those words mean to them. Density is always cumbersome. They get the idea that more dense things sink, but verbalizing the concept alone is often very challenging. In fact one class never was able to tell me what density was.
We also talk about flammability, and how this is a property of some types of matter. We also talk about what is needed for something to burn: fuel, oxygen, and an ignition source. This brings up the idea for chemical reactions and how a chemical property is not the same as a physical one (though I do not call them this right now.)
It’s a neat demo to get the juices flowing.
Chemistry: We started the Pressure labs today. Today was Boyle’s Law (P v. V). We use Vernier Gas Pressure sensors hooked up via a LabPro to collect data and make the graphs. Students see that there is an interesting relationship, inverse to be specific. They can verbalize it to me, and as such I tell them to write up A) what is the relationship, and B) do particle diagrams that illustrate what is happening.
Tomorrow we look at the amount of gas and how it affects pressure.
Physics of Light: Today we looked at the results of their investigation from yesterday. For looking at and defining Real Images they came up with: Forms at the point where light rays converge, is upside down compared to the object, can bee seen with a screen, but is also viewable if you are within the “cone of light” that makes up the extreme boundaries of light that leaves the convergence points.
We also looked at the differences between the real image and the reproductions we saw earlier in the year. Reproductions require a screen, and can be seen at any screen position (real images can only be seen on the screen if the screen is placed at the point where the real image forms.)
They also found that covering up the lens only affects the brightness of the image (a reproduction would be cut in half. Also, putting foil with holes in it by the lens, still only makes 1 image (different from the pinhole reproductions.)
We also talked about the idea that the real image, since it is viewable without the screen, can be seen as “floating in air.” By looking closely at it, you can actually tell the depth of the image form the lens. We then went over to the lab station and kids tried to find the image by spying it in the air. This is why we also refer to real images as Aerial Images.
At this point, I passed out the new homework packet. I pointed out that I wanted to look closely at the second question. Question 1 is just like the handout they got on Monday, where the object is super far from the lens. Question 2 has the object super close (within the focal point.) Right away the kids noticed (at least those NOT working on Question 1) that the rays diverge after going through the Converging Lens.
“So what would you see if you looked at this setup?”
“Nothing. It must be total internal reflection!”
So we went back to the lab, and I said to look at the setup and see what things looked like. This turned out to be more difficult than anticipated. First, kids looked at the lens, and thought that what they were seeing on the other side of the lens was just the light source. The did not notice the difference in size, nor did they notice the difference in depth from the lens. There was also an issue of a secondary light source creating an extremely small and faint real image, that some kids just couldn’t ignore. So overall this did not go well.
So back to the drawing board, literally.
“Okay, for starters there is no real image, or at least there shouldn’t have been.”
“Can we figure out why there was?”
“Yeah some other day. NOW, lets focus on the problem at hand. The light diverges, but it would still hit our eyes right?”
“So here’s a news flash: Light travels in straight lines, unless it gets bent or reflected, but while we KNOW this, our brains DON’T know this. Our brains only see light as having traveled in straight lines. So if we trace these bent rays back ward…”
Then we see convergence points on the same side of the lens as the object. It also, if true, gives us an upright and larger object. It fits what we see when we look through the lens.
“This would be your classic magnifying glass.”
Tomorrow we are going to look at diagrams with Diverging Lenses.