College-Prep Physics: Today we used the data from our sunspot log to determine how fast the sun rotates. Do the sunspots speed up, slow down, or move at constant speed? Do all places on the sun rotate at the same rate or does it depend on latitude? The lab handout is here: LAB Solar Rotation 2013
Conceptual Physics: Students used the PhET circuit simulation to explore how current and voltage behave differently in series and parallel circuits.
AP Physics C: Practice AP free response questions on Faraday’s Law.
College-Prep Physics: It was sunny out today! So we poked a hole in the side of a copy paper box to make a pinhole camera. Aimed our cameras at the sun and measured the resulting image in order to determine the true size of the sun. The copy paper box worked beautifully: the sides with the hole and the screen are always parallel; it’s easy to aim the camera directly at the sun — lay box on ground and lift up/turn until box shadow is square; for the size of the box, the image of the sun is exactly 1/2 cm across (so it fits perfectly within 1/2 cm graph paper). We didn’t do anything fancy with foil like I’ve seen for other pinhole cameras on the internet. Should we have? Why?
Conceptual Physics: Students finished the diode circuit simulation activity from yesterday. One group came up with a possible bike generator circuit that will charge the battery and light the bulb while pedaling, and will also use the battery to light the bulb when the pedaling stops.
College-Prep Physics: A wax photometer (two parafin blocks taped together with foil in between) is a neat little device which can show you the relative light intensity of two light sources. When the light intensity is equal on both sides of the photometer, the wax blocks are illuminated equally:
When one of the lights is moved twice as far away, the wax blocks are of unequal brightness:
How many light bulbs would need to be added to the left side so the light intensity on both sides of the block would be equal again? Based on yesterday’s investigation, we saw that when distance changes by factor n, the light intensity changes by factor 1/n2. So, in this case, we’d need four bulbs on the left side:
What was amazing was that a student then asked, “Could we do this comparison with the sun?” … which is exactly what I had planned 🙂 . Groups of students took turns going outside and repeating the experiment with the wax phototometer and a 200 watt bulb in order to calculate how many 200 watt lightbulbs would be as bright as the sun (first picture).
Conceptual Physics: Students began drafting possible circuit designs to modify the bike light generator so that: 1) a battery lights the bulb when the rider is not pedaling and 2) that battery gets recharged while the rider is pedaling.