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Monday, March 28, 2016

'Smarter Every Day' video on some different magnetic tidbits!

This comes to us thanks to Marc B., a former student who loved magnetism and still spends (too much, in his words) time watching anything he finds on the topic. It is perfect for us since we are wrapping things up with magnetism! Check it out! By the way, the website for the polymagnets company, which custom designs magnets with any configuration, is here.

Monday, March 21, 2016

Sir Ken Robinson on Creativity (or the lack thereof) in Schools

This is one of my favorite TED talks. Keep in mind creativity and innovation are two of the most important 'skills' or qualities students need to develop in this globalized, technological economy. Let me know what you think!

A few interesting EM induction examples

As we study electromagnetic induction, a developing technology application is wireless charging, which can go by the name of wireless power or inductive charging. This process uses electromagnetic fields to induce charge in devices, so there is no need for physical contact (hence the use of 'induction'). Presumably this would need to make use of AC currents, in order to cause changes in flux (and apply Faraday's law of em induction).

How do inductive stoves work, where the stove would not necessarily be warm/hot to the touch, but put a copper pot on it and the pot heats up rapidly?!

Another famous example is an electromagnetic pulse, or EMP. These are bursts of electromagnetic energy, and many phenomena can produce such bursts, from lightning to solar flares to nuclear blasts. These can cause damage to electronics systems, for instance, since currents will be induced in circuitry.

Think about where else there could be induction phenomena in your life!

Friday, March 18, 2016

For Classes on March 18

Happy Friday everyone!

Periods 1-2, 8-9:
Yesterday you saw something on Faraday's law for a moving hoop/changing area example. This is the case where induced voltage = B dA/dt. Today extend on this by looking at cases where a second force is trying to push a circuit through magnetism, such as dropping a metal hoop into a B-field. What you will see is that, because this process depends on speed, it ends up looking a lot like air friction and terminal velocity from last year! Weird, but true. Remember the case of you trying to swing the metal hoop through the big magnet, and you felt the forces on it trying to slow it down (this is a magnetic brake). Take good notes so you can try to make sense together of the home work problems - see if you can complete things before leaving.

Homework set: 
The glider problem on page 6 is based on yesterday - use the notes on page 2 and 3, could be helpful
The 1990 problem on page 7 - notes on page 4 could be helpful
The challenge problem is on page 9! Have fun!

Periods 3-4:

Take a look at the problems for yesterday, and see if there is any consensus. Ampere's law depends on the current inside the region you are looking at, analogous to Gauss's law depending on teh charge inside the region.

One application of Ampere's law for straight wires, where B = (mu)I/(2*pi*r), is to get the force between two currents. Check out a video on the forces between two long wires with currents - they are both producing magnetism, so the wires should either attract or repel each other! Take good notes, this will be needed for some of the homework. Note that the force on currents is F = IL x B, where L is the length of a segment of the wire.

Then, take a look at a video on the initial exposure to Biot-Savart law. This is the rule that allows us to determine the magnetic field for things more exactly (Ampere is only for long wires, solenoids, and toroids, so it is limited). We will look at what a single moving particle does in terms of producing a magnetic field. Take good notes, because we will build on this.

Try the following from the packet:
Ch. 28 #8 (B-S law), 31 on page 7
AP Prob from 1983, page 11

Thursday, March 17, 2016

Classes for March 17

Periods 1-2 and 8-9:

We will dive into the electromagnetic induction material! Check out two videos, for the case where we have a constant magnetic field and a moving chunk of metal or circuit. This is the case of
emf = induced voltage = -B dA/dt. The first is about just moving a piece of metal through a magnetic field. The second is about moving a circuit into or out of a B-field, where the area is changing. Take good notes, and you can try AP problems from 1981 and 1984 (pages 5 and 8 in the packet).

Also, start doing an error analysis on the last magnetism quizzam (solutions have been on the web site).

Periods 3-4:
3rd period you will need to do the school survey. After this, check with each other about answers to last night's set. Once done, then watch a video and take notes on Ampere's law - this is similar to Gauss's law for electric fields, only for magnetism!

Try the AP problems on pages 8 and 9 in the packet from yesterday.

Monday, March 7, 2016

Some links for classes the week of March 8-11

While Doc V is out of town, here are some links:

Periods 1-2, 6-7, 8-9:

On Tuesday, after reaching consensus on the homework problems, check out a video on rolling without slipping. This is the type of motion we would expect to have for things that roll. When there is NO SLIPPING, this means we have no heat being generated, and we can use the relationships s = R*(theta), v = Rw, a = R*(alpha). Take good notes, and feel free to replay any parts that are confusing. Also, on the blog is a video on the equilibrium stuff we did last week (balancing torques), in case anyone wants to see another example of left = right, up = down, and cw = ccw.

After watching the video, see if you can make it through the 1997 problem on page 18 of our packet; work in small groups to see if the video made any sense. Then you can try some of the homework problems before leaving: Page 13 of packet, Ch. 9 #83 or 84 (choose one); and page 14 of packet, the AP Problem from 2002. These all make use of energy! Remember, the only new thing is adding in (1/2)Iw^2 for rotational motion.

On Wednesday and Thursday, Adam is in!! For links to the lesson, go to Adam's web page. Have phun!

On Friday, someone can pull up the solutions to the 2002 problem from Tuesday and see how it went together. Then check out a video on something tipping over, with NON-constant angular acceleration. Take notes on this. You will then have time to try a problem from 1999, on page 15, which builds off the video. Also, you can take a look at the problem on page 19, from 1994, making use of a few ideas from energy.

Periods 3-4:

On Tuesday, before going back to the lab, check out a video on charged particles moving through magnetic fields (B-field). Take good notes, we will be using those later. Then get back into the lab and try to complete it before leaving. You will need the data from the graph portion for when Adam is here Wednesday and Thursday.

For homework, try to make sense of the Band Theory Review on page 3 of our packet. This gets into the difference between conductors, insulators, and semiconductors from a quantum point of view. Check out the video on this band gap theory as a guide, and try to summarize it on page 3.

On Wednesday and Thursday, Adam is in!! For links to the lesson, go to Adam's web page. Have phun!

On Friday, watch the Nova video called "Magnetic Storm," and answer the questions on page 10 of the packet. These will be collected next week. If there is time, there is also a video on mass spectrometers which you should watch in class (or at home if not enough time), in order to do the homework problem on page 13 (from 1984).

Thank you all for your cooperation this week, and for all the support! I am really proud of and thankful for each of you! I cannot wait to come back and have some discussions about all we are working on out in Dubai.