B and F Blocks discussed the topic of electric power and why companies deliver electrical energy at high voltages rather than high currents to reduce the energy per time (power) that is converted to heat and lost as usable energy. We took a look at a sample electric bill and how the unit of the kilowatt-hour compares to the unit of the Joule for energy. Tomorrow, F Block works a lab to better understand Ohm's Law and the difference between ohmic and non-ohmic substances, while B Block starts their work on electrical circuits.
E Block started their electrical circuits discussion today with an overview of the nature of circuits, the structure and function of a schematic diagram, the difference between open and closed circuits and the danger of short circuits. Tomorrow, we'll look at one specific type of circuit - the series circuit - and investigate its properties both conceptually and mathematically.
C Block took up the topic of resistance today with a discussion about the nature of resistance, the factors that affect a material's resistance and Ohm's Law. We used our previous work in the Ohm's Lab to better understand the relationship between potential difference and current that Ohm's Law describes and what was different about substances that were classes as non-ohmic. We ended the class with an overview of the property of superconductivity and how it could revolutionize technology, if only we could find materials with reasonable critical temperatures. Tomorrow - electric power!
4/30/12
4/29/12
4/27/12
We're Everywhere
Classes are in different places now, but that's fine. Everyone will end up at the finish line on time.
B and F Blocks took up the idea of electrical resistance and Ohm's Law. For B Block, this came on the heels of yesterday's Ohm's Law lab, so that lab was used to illustrate the principles in this section. Make sure you understand the concept of resistance, what Ohm's law says about the relationship between resistance, voltage and current, the difference between ohmic and non-ohmic substances and factors that influence an object's resistance. We also jumped into the arena of superconductors, touching on their properties and potential uses.
C Block moved officially into the electrical current zone with a discussion of the nature of current, the concept of drift velocity and the difference between alternating and direct current. On Monday, we add resistance to the mix and remind ourselves of the results you obtained in your Ohm's Law lab.
E Block looked at the idea of electrical power. We're still talking about the rate at which work is done, but this time the work is being done by or on electrical charges through transformations of energy. Joule heating (also called I2R loss) was examine and used to explain why power companies deliver electricity at high voltages and not high currents. On Monday, we take up the task of examining the fundamentals of electric circuits.
B and F Blocks took up the idea of electrical resistance and Ohm's Law. For B Block, this came on the heels of yesterday's Ohm's Law lab, so that lab was used to illustrate the principles in this section. Make sure you understand the concept of resistance, what Ohm's law says about the relationship between resistance, voltage and current, the difference between ohmic and non-ohmic substances and factors that influence an object's resistance. We also jumped into the arena of superconductors, touching on their properties and potential uses.
C Block moved officially into the electrical current zone with a discussion of the nature of current, the concept of drift velocity and the difference between alternating and direct current. On Monday, we add resistance to the mix and remind ourselves of the results you obtained in your Ohm's Law lab.
E Block looked at the idea of electrical power. We're still talking about the rate at which work is done, but this time the work is being done by or on electrical charges through transformations of energy. Joule heating (also called I2R loss) was examine and used to explain why power companies deliver electricity at high voltages and not high currents. On Monday, we take up the task of examining the fundamentals of electric circuits.
4/26/12
Current and Resistance Onward
B Block was introduced to the concept of electrical resistance through a lab on Ohm's Law. For some substances, the ratio of potential difference to current is fixed and the proportionality constant is the resistance of the system. Not all substances follow this relationship for all potential differences and these substances, like light bulb filaments, are termed non-ohmic. You found that the slopes of the lines for the resistors were close to the stated resistance values, and the light bulb showed two resistances, one at low voltages and another at higher values. Folks also tested an LED and a Zener diode to see their how they played in the current/voltage pool and found that current flowed in one direction. Diodes can be thought of as valves, permitting current flow in one direction. The Zener diode, however, did let current flow when you crested 5V. Zener diodes have a breakdown voltage that will allow the release of current above a certain value, without damaging the component. Standard diodes can be damaged if current is forced backwards. Tomorrow, we'll discuss the nature of resistance, factors that affect an object's resistance and dip our toes into the topic of superconductivity, where zero resistance can be reached when we dip below a certain critical temperature.
That last part was the focus of E-Blocks's work today. We defined resistance and looked at factors (length, diameter, temperature and identity of material) that impact an object's resistance. Make sure you know specifically how these factors affect resistance and be able to compare objects resistances based on their construction. We took on Ohm's Law, which sets the resistance value for a substance based on the ratio of supplied potential difference and observed current flow, and contrasted ohmic and non-ohmic substances. We then looked at the absence of resistance for the topic of superconductivity and some possible applications if we can only make superconductivity a financially-viable option for large-scale use. Tomorrow - electric power!
C Block reviewed their Ohm's Law lab then had time to work on test corrections. F Block started their journey into electric current through defining current, looking at the concept of conventional current and direction of charge-carrier motion and discussing why the actual velocity of charges in a system is much lower than we would predict. We ended by contrasting alternating and direct current and discussing examples of where each is used. Tomorrow, we add the property of resistance to our electricity grab bag and one new formula - Ohm's Law.
That last part was the focus of E-Blocks's work today. We defined resistance and looked at factors (length, diameter, temperature and identity of material) that impact an object's resistance. Make sure you know specifically how these factors affect resistance and be able to compare objects resistances based on their construction. We took on Ohm's Law, which sets the resistance value for a substance based on the ratio of supplied potential difference and observed current flow, and contrasted ohmic and non-ohmic substances. We then looked at the absence of resistance for the topic of superconductivity and some possible applications if we can only make superconductivity a financially-viable option for large-scale use. Tomorrow - electric power!
C Block reviewed their Ohm's Law lab then had time to work on test corrections. F Block started their journey into electric current through defining current, looking at the concept of conventional current and direction of charge-carrier motion and discussing why the actual velocity of charges in a system is much lower than we would predict. We ended by contrasting alternating and direct current and discussing examples of where each is used. Tomorrow, we add the property of resistance to our electricity grab bag and one new formula - Ohm's Law.
4/25/12
Electric Current
B and E Blocks began their journey through the wild and wacky world of electric current. We discussed that nature of current, the difference between charge motion and conventional current, the concept of drift velocity and the features characterizing direct and alternating current. Make sure you can work with the basic current formula and recognize that current is a rate function - the rate of charge motion through a particular area. Tomorrow, B and E Blocks add the idea of electrical resistance to the growing descriptors of charge motion. B Block will do it with a lab focusing on Ohm's Law and E Block will walk through the concept in lecture.
C Block conducted their Ohm's Law lab in class today. Ohm's law relates potential difference (voltage), current and resistance and this relationship, for some substances, is constant. Written in terms of resistance, Ohm's Law states: R = V/I and a graph of voltage versus current should yield a linear relationship for which the slope is the resistance. For your resistors, this was definitely the case, but for the light bulb, the early and later sections of the graph had different slopes. Some substances are non-ohmic, they do not behave Ohm's Law across all ranges of input voltages. We'll discuss this in more detail later in this chapter. Have the write-ups for me tomorrow and you'll have time in class to work on test corrections. That's what F Block did today, so you'll get the same chance.
C Block conducted their Ohm's Law lab in class today. Ohm's law relates potential difference (voltage), current and resistance and this relationship, for some substances, is constant. Written in terms of resistance, Ohm's Law states: R = V/I and a graph of voltage versus current should yield a linear relationship for which the slope is the resistance. For your resistors, this was definitely the case, but for the light bulb, the early and later sections of the graph had different slopes. Some substances are non-ohmic, they do not behave Ohm's Law across all ranges of input voltages. We'll discuss this in more detail later in this chapter. Have the write-ups for me tomorrow and you'll have time in class to work on test corrections. That's what F Block did today, so you'll get the same chance.
4/24/12
Test Day
Today was everyone's Chapter 17 and 18 exam and everyone starts with Chapter 19 tomorrow. This next chapter centers on electric current and resistance, a prelude to our work with electric circuits in Chapter 20. C Block has lab tomorrow and that investigation will focus on Ohm's Law, which pulls the three biggies in electricity together in one package - voltage, current and resistance. The reading you were assigned for tonight (p. 700-701) goes over Ohm's Law and should help you with the discussion questions/conclusion for the lab.
4/23/12
And... We're Back
Today was a big' ol review day for tomorrow's exam for B, C and F. Do make use of the previously-posted videos for electric fields and forces and look through the ones in the last post for general review, especially if you weren't in class today.
E Block worked on their Capacitors lab for which the write-up isn't due until Thursday. Capacitors separate charges when exposed to a potential difference and, therefore, act as storehouses of electrical potential energy when the plates are reconnected by a conducting wire. The RC-time constant concept won't appear on the test tomorrow, but basic ideas about capacitance, capacitors and potential energy will be addressed.
On Wednesday, we all start electric current with C Block working on a lab centering on Ohm's Law.
E Block worked on their Capacitors lab for which the write-up isn't due until Thursday. Capacitors separate charges when exposed to a potential difference and, therefore, act as storehouses of electrical potential energy when the plates are reconnected by a conducting wire. The RC-time constant concept won't appear on the test tomorrow, but basic ideas about capacitance, capacitors and potential energy will be addressed.
On Wednesday, we all start electric current with C Block working on a lab centering on Ohm's Law.
4/21/12
Chapter 17-18 Review
Here's are a couple of videos for reviewing Chapter 17 and 18 material. Get your book out and follow along - it's the same thing we do in class, but maybe it will help some folks. You can up the size to full screen if you want, but don't expect great resolution either way. I'm too lazy to experiment much with my new software while I'm still on vacation, so cut me some slack. Don't forget that there were videos to help you with some of the problem solving that were posted earlier. Jump back to older posts (use The.Archive in the sidebar) to find those videos.
4/20/12
Very Well Said, Sir
This is the text of Tom Hiddleston's article in the UK's Guardian in defense of superhero films. He played Loki in Thor and reprises the role in the upcoming Avengers. If more actors were this articulate, I think critics would have a much harder time trashing movies like those...
Earlier this year, beneath the wind-whipped tarpaulin of a catering tent in Gloucester, I was working on a film with the actor Malcolm Sinclair. Over scrambled eggs at an ungodly hour, he told me something I had not previously known: when Christopher Reeve was young, barely out of Juilliard, he was roundly mocked by his peers on Broadway for accepting the role of Superman. It was considered an ignoble thing for a classical actor to do.
I grew up watching Superman. As a child, when I first learned to dive into a swimming pool, I wasn't diving, I was flying, like Superman. I used to dream of rescuing a girl I had a crush on (my Lois Lane) from a playground bully (General Zod). Reeve, to my mind, was the first real superhero.
Since then some of the greatest actors have turned superheroes into a serious business: Michael Keaton and Jack Nicholson in Batman; Ian McKellen and Patrick Stewart, the first venerable knights of the X-Men, who have now passed the baton to Michael Fassbender and James McAvoy. In spite of 20 years of mercurial work in the likes of Chaplin and Kiss Kiss Bang Bang, it was his rock-star-charismatic yet somehow humble Tony Stark in Iron Man that helped wider audiences finally embrace the enormous talent of Robert Downey Jr. And Heath Ledger's performance in The Dark Knight quite simply changed the game. He raised the bar not just for actors in superhero films, but young actors everywhere; for me. His performance was dark, anarchic, dizzying, free, and totally, thrillingly, dangerous.
Actors in any capacity, artists of any stripe, are inspired by their curiosity, by their desire to explore all quarters of life, in light and in dark, and reflect what they find in their work. Artists instinctively want to reflect humanity, their own and each other's, in all its intermittent virtue and vitality, frailty and fallibility.
I have never been more inspired than when I watched Harold Pinter speak in a direct address to camera in his Nobel lecture in 2005. "Truth in drama is forever elusive. You never quite find it but the search for it is compulsive. The search is clearly what drives the endeavour. The search is your task. More often than not you stumble upon the truth in the dark, colliding with it or just glimpsing an image or a shape which seems to correspond with the truth, often without realising that you have done so. But the real truth is that there never is any such thing as one truth to be found in dramatic art. There are many. These truths challenge each other, recoil from each other, reflect each other, ignore each other, tease each other, are blind to each other. Some times you feel you have the truth of a moment in your hand, then it slips through your fingers and is lost."
Big talk for someone in a silly superhero film, I hear you say. But superhero films offer a shared, faithless, modern mythology, through which these truths can be explored. In our increasingly secular society, with so many disparate gods and different faiths, superhero films present a unique canvas upon which our shared hopes, dreams and apocalyptic nightmares can be projected and played out. Ancient societies had anthropomorphic gods: a huge pantheon expanding into centuries of dynastic drama; fathers and sons, martyred heroes, star-crossed lovers, the deaths of kings – stories that taught us of the danger of hubris and the primacy of humility. It's the everyday stuff of every man's life, and we love it. It sounds cliched, but superheroes can be lonely, vain, arrogant and proud. Often they overcome these human frailties for the greater good. The possibility of redemption is right around the corner, but we have to earn it.
The Hulk is the perfect metaphor for our fear of anger; its destructive consequences, its consuming fire. There's not a soul on this earth who hasn't wanted to "Hulk smash" something in their lives. And when the heat of rage cools, all that we are left with is shame and regret. Bruce Banner, the Hulk's humble alter ego, is as appalled by his anger as we are. That other superhero Bruce – Wayne – is the superhero-Hamlet: a brooding soul, misunderstood, alone, for ever condemned to avenge the unjust murder of his parents. Captain America is a poster boy for martial heroism in military combat: the natural leader, the war hero. Spider-Man is the eternal adolescent – Peter Parker's arachnid counterpart is an embodiment of his best-kept secret – his independent thought and power.
Superhero movies also represent the pinnacle of cinema as "motion picture". I'd like to think that the Lumière brothers would thrill at the cat-and-mouse chase through the netherworld streets of Gotham in The Dark Knight, with helicopters tripping on high-tensile wires and falling from the sky, and a huge Joker-driven triple-length truck upending 180 degrees like a Russian acrobat. I hope that they would cheer and delight at the rollercoaster ride through the skies of Manhattan at the end of Avengers Assemble. These scenes are the result of a creative engine set in motion when the Lumières shot L'Arrivée d'un Train en Gare de la Ciotat in 1895. The trains just move a lot faster these days. And not just trains; trucks, bikes, bat-mobiles and men in flying, shining iron suits. The spectacle is part of the fun – part of the art, part of our shared joy.
How far I hope we have come since the judgment of Christopher Reeve's peers. Maybe playing superheroes isn't such an ignoble undertaking after all. "I still believe in heroes," says Samuel L Jackson's Nick Fury in Avengers Assemble. So do I, sir. So do I.
4/19/12
RIP Jonathan Frid
This one hurts. Jonathan Frid was the vampire most folks my age grew up with because we watched Dark Shadows religiously. This was the most bizarre show on television - a daytime soap opera that revolved around a 200-year old vampire and his "modern day" family. The show ran from 1966 - 1971 and the character of Barnabas Collins was actually introduced in 1967, to help with flagging ratings. The show was, up to that point, a gothic mystery sort of thing and Barnabas was only supposed to be in the show a short while. The character wound up being the star and... it was just great. I had the board game and it was my absolute favorite:
There was a revival of this show in the 90's starring Ben Cross that wasn't bad, but it only lasted one season. The original also spawned a couple of tie-in movies that are more campy fun. Netflix has the original series for streaming, so you can check out what the fuss is about. Barnabas Collins is officially introduced in episode 210, but really makes his entrance in episode 211. You can watch that episode by following this link:
Dark Shadows Episode 211
The previews for the new Dark Shadows movie are strange, to say the least. I hope Jonathan would be proud (has a cameo in that film - last appearance before his death).
There was a revival of this show in the 90's starring Ben Cross that wasn't bad, but it only lasted one season. The original also spawned a couple of tie-in movies that are more campy fun. Netflix has the original series for streaming, so you can check out what the fuss is about. Barnabas Collins is officially introduced in episode 210, but really makes his entrance in episode 211. You can watch that episode by following this link:
Dark Shadows Episode 211
The previews for the new Dark Shadows movie are strange, to say the least. I hope Jonathan would be proud (has a cameo in that film - last appearance before his death).
4/18/12
4/13/12
Finally!
Friday the 13th and the day before April vacation - quite a contrast...
B and C Blocks finished up their electrostatic unit with a discussion of capacitors and capacitance. Capacitors store charge to release on command. While the charges are separated on the capacitor plates, the capacitor also acts as a storehouse of electric potential energy, which can become useful work when the plates are connected by a wire so charges can move. We'll review the idea of capacitors and capacitance when we return from break.
F Block worked on their capacitor lab, examining how the combination of a resistor and capacitor affects the charge/discharge rate for the capacitor. Don't worry about working on these over break, you'll have time when we return.
E Block worked on some problems that tossed out little twists or brought back old friends, like kinetic energy. Nice relaxing period where the only thing at work was the brain...
Have a fun and safe vacation - see you in a week!
B and C Blocks finished up their electrostatic unit with a discussion of capacitors and capacitance. Capacitors store charge to release on command. While the charges are separated on the capacitor plates, the capacitor also acts as a storehouse of electric potential energy, which can become useful work when the plates are connected by a wire so charges can move. We'll review the idea of capacitors and capacitance when we return from break.
F Block worked on their capacitor lab, examining how the combination of a resistor and capacitor affects the charge/discharge rate for the capacitor. Don't worry about working on these over break, you'll have time when we return.
E Block worked on some problems that tossed out little twists or brought back old friends, like kinetic energy. Nice relaxing period where the only thing at work was the brain...
Have a fun and safe vacation - see you in a week!
4/12/12
Potential Difference and Capacitance
B and C Blocks took on the topic of batteries and potential difference. We discussed the structure and function of a battery (or other power supply) in an electric circuit and how that function was based on the concept of potential difference. Expose charges to a potential difference and you promote motion in the direction of the low electric potential area in the circuit which, for a battery, is the positive terminal. Tomorrow, we'll look at another component of electric circuits - the capacitor and show how they function as a storehouse of electric potential energy.
F Block had that discussion today, looking at the property 'capacitance' and how certain devices are built to have certain capacitance values, based on their function in a circuit. Capacitance describes how much charge can be stored for a specific potential difference and is independent of charge - more charge, more voltage; less charge, less voltage. We looked at some examples of capacitors and that will be the focus of our lab work in class tomorrow.
E Block reviewed their capacitors homework and took a walk back through the topics in Chapter 17 and 18 in preparation for the exam. Tomorrow, we'll get some more math practice on these topics and, on the Monday we return from vacation, there will be labwork on capacitors in electric circuits.
F Block had that discussion today, looking at the property 'capacitance' and how certain devices are built to have certain capacitance values, based on their function in a circuit. Capacitance describes how much charge can be stored for a specific potential difference and is independent of charge - more charge, more voltage; less charge, less voltage. We looked at some examples of capacitors and that will be the focus of our lab work in class tomorrow.
E Block reviewed their capacitors homework and took a walk back through the topics in Chapter 17 and 18 in preparation for the exam. Tomorrow, we'll get some more math practice on these topics and, on the Monday we return from vacation, there will be labwork on capacitors in electric circuits.
4/11/12
Batteries and Capacitors
C Block was the odd-man out today, as they worked through the ideas of electric potential energy, electric potential and potential difference. Make sure you are very clear about each definition and the associated formulas. Between this chapter and last chapter, formulas look very similar and it is easy to get them mixed up on a test. Tomorrow, we'll extend the discussion of potential difference to the concept of batteries and power supplies - what role does a battery have in an electric circuit? Stay tuned and find out.
B Block finished up their capacitor lab, with write-ups due on Friday. Capacitors store charge and discharge on command, which is why they are great for turn signals and computer keys. Think about the RC relationship and what that means for capacitors charging and discharging and why linking two capacitors in series altered the RC value for the circuit. Tomorrow, we'll jump back into our discussion of potential difference and look at that battery potion of your circuit in more detail.
E Block took on the topic of capacitors and you'll work on your capacitor lab on the Monday we return from break. Capacitors act as storehouses of charge and the associated potential energy. When you need work done, you release the charge. We discussed factors that affect an object's capacitance (size, shape, plate spacing, permittivity of materials) and how to calculate various properties of capacitors. We'll go over these problems tomorrow before starting a general review of the material for your next exam. Friday, we'll start your capacitor lab, which we'll conclude when we return from break.
F Block linked yesterday's work on potential difference to the concept of a battery or power supply. Batters offer points of high and low electric potential that create the potential difference to stimulate charge flow. We looked at different types of batteries and clarified what voltage means for a battery and took a little time to preview the ideas of direct and alternating current. Tomorrow, we'll hit the idea of capacitors and Friday's lab will use ideas about capacitors and potential difference to look at how capacitors function in circuits.
B Block finished up their capacitor lab, with write-ups due on Friday. Capacitors store charge and discharge on command, which is why they are great for turn signals and computer keys. Think about the RC relationship and what that means for capacitors charging and discharging and why linking two capacitors in series altered the RC value for the circuit. Tomorrow, we'll jump back into our discussion of potential difference and look at that battery potion of your circuit in more detail.
E Block took on the topic of capacitors and you'll work on your capacitor lab on the Monday we return from break. Capacitors act as storehouses of charge and the associated potential energy. When you need work done, you release the charge. We discussed factors that affect an object's capacitance (size, shape, plate spacing, permittivity of materials) and how to calculate various properties of capacitors. We'll go over these problems tomorrow before starting a general review of the material for your next exam. Friday, we'll start your capacitor lab, which we'll conclude when we return from break.
F Block linked yesterday's work on potential difference to the concept of a battery or power supply. Batters offer points of high and low electric potential that create the potential difference to stimulate charge flow. We looked at different types of batteries and clarified what voltage means for a battery and took a little time to preview the ideas of direct and alternating current. Tomorrow, we'll hit the idea of capacitors and Friday's lab will use ideas about capacitors and potential difference to look at how capacitors function in circuits.
4/10/12
Energy and Charges
C Block reviewed their lab work and homework from Friday and more time was allotted for practice with electric fields and forces. The video below is for the practice problem you worked on in class - use it if you get stuck trying to solve that problem. Tomorrow, we'll move on to electric potential energy, electric potential and potential difference.
B Block worked on their capacitor lab and will get more time to finish up tomorrow. Capacitors store charge and discharge when the right signal is given. The RC- time constant reflects the rapidity of the charge/discharge and that is influenced by the size of the resistor and capacitor. Wiring capacitors in series or parallel also has an effect (by altering the value for the overall capacitance) and you'll see that tomorrow. The write-ups will be due on Friday, so you might want to make sure to read the capacitors section in this chapter before scripting the conclusion section.
E Block took on the topic of batteries, today. Batteries are sources of potential difference in a circuit. They promote charge flow
B Block worked on their capacitor lab and will get more time to finish up tomorrow. Capacitors store charge and discharge when the right signal is given. The RC- time constant reflects the rapidity of the charge/discharge and that is influenced by the size of the resistor and capacitor. Wiring capacitors in series or parallel also has an effect (by altering the value for the overall capacitance) and you'll see that tomorrow. The write-ups will be due on Friday, so you might want to make sure to read the capacitors section in this chapter before scripting the conclusion section.
E Block took on the topic of batteries, today. Batteries are sources of potential difference in a circuit. They promote charge flow
4/9/12
Charging on With Charge
B and E Blocks entered the world of electric potential energy today. Particle have potential energy based on their position in an electric field and changing that position will cause the value of the potential energy to change. Since work is being done on or by an object when potential energy changes, we can liken this to charges doing work (like powering a lightbulb) or having work done on them (moving through a battery). We distinguished PEelec from electric potential (PEelec/q) and potential difference (ΔPEelec/q). We'll work with potential difference a lot in the coming weeks as we move through ideas of electric current and circuits. In lab tomorrow for B Block, potential difference will help students investigate the properties of a capacitor, calculating the RC time constant for a variety of capacitor-resistor combinations. E Block jumps into the area of batteries and how potential difference makes them work.
C Block conducted their static electricity lab, investigating how objects can acquire charge through friction, conduction and induction, and how the resulting forces can cause changes in the motion of matter. If you didn't hand this in today, remember to have it tomorrow, along with the additional homework items I put on the board.
F Block spot-checked their problem-solving skills for electric fields and forces. make sure you can calculate the net electric field at a point in a field of particles and the force on a charge particle resulting from multiple charges. Tomorrow, we expand on our discussion of charges to bring in energy and changes in energy due to particle motion.
C Block conducted their static electricity lab, investigating how objects can acquire charge through friction, conduction and induction, and how the resulting forces can cause changes in the motion of matter. If you didn't hand this in today, remember to have it tomorrow, along with the additional homework items I put on the board.
F Block spot-checked their problem-solving skills for electric fields and forces. make sure you can calculate the net electric field at a point in a field of particles and the force on a charge particle resulting from multiple charges. Tomorrow, we expand on our discussion of charges to bring in energy and changes in energy due to particle motion.
4/6/12
One Stunted Day
With the half-day schedule, only B and C Blocks met. B Block was given some brain-buster problems dealing with electric forces and fields that tied in some former labwork with our newly-practiced vector skills. C Block, with an extend period, got to investigate electric circuits with SnapCircuits kits. Students built a conductor meter, a UFO launcher, a doorbell and two other projects of their choice. We'll spend quite a bit of time looking at electric circuits in a later chapter and work with the associated math, but this gives you nice preview of what electric circuits are and what they can do.
4/5/12
Electric Fields
B, C and F Blocks took time to discuss electric fields. Electric forces are generated when charges enter another charge's electric field. To measure fields, we use a tiny positive test charge and watch the effects. We looked at how to determine the direction of an electric field and what to do when multiple charges contribute to an electric field. Time was also taken to address the influence of an object's shape on its electric field. Sharp points have stronger electric fields and that explained why certain things are more prone to get struck by lightning that others. B and C Blocks will start electric potential and electric potential energy tomorrow, but F Block will have to wait until Monday, since they won't be in class due to the half-day release schedule.
E Block worked on their Discharge Rate lab during the long block. When scientists make observations, they have to find ways to describe them quantitatively and there may be more than one way, depending on the information they have. You looked at several ways of calculating the size of the electric force acting on a particle and then how to use that information to calculate a particle's charge. As objects lose charge to the environment, we would expect the size of their electric field and force would diminish and that, for this lab, meant the charged spheres would draw closer together. The discharge rate documents how quickly or slowly an object loses its charge and an analysis of your graphs and equations gave you that information. We'll discuss the lab on Monday before jumping into the idea of electric fields.
4/4/12
A Day of Variety
Code Blue drill during A Block, electric force practice during B Block, test correction work during C Block, electric fields during E Block and F Block worked on a plethora of static electricity labs... whew...
B Block - make sure you nail down those electric forces problem-solving skills. Good review of vector techniques and properties of electric forces. If you need to, review the videos presented a few posts ago for problem-solving ideas. Tomorrow - electric fields.
E Block took on electric fields today after tying up loose ends with electric forces. You should be able to determine the size of an electric field at a location when it is created by a single charge or is the product of multiple charges. Be comfortable with evaluating electric field lines and discussing how charges distribute themselves on different shaped objects. We'll go over the homework tomorrow before moving to the next chapter and starting a discussion of electric potential energy.
F Block spent the long block conducting a number of experiments that highlighted aspects of static electricity. Different methods of charging were used to generate charge on neutral objects and the action of electric forces, both attracting and repelling, were observed. Tomorrow, we'll look at what is behind the generation of electric forces - electric fields.
B Block - make sure you nail down those electric forces problem-solving skills. Good review of vector techniques and properties of electric forces. If you need to, review the videos presented a few posts ago for problem-solving ideas. Tomorrow - electric fields.
E Block took on electric fields today after tying up loose ends with electric forces. You should be able to determine the size of an electric field at a location when it is created by a single charge or is the product of multiple charges. Be comfortable with evaluating electric field lines and discussing how charges distribute themselves on different shaped objects. We'll go over the homework tomorrow before moving to the next chapter and starting a discussion of electric potential energy.
F Block spent the long block conducting a number of experiments that highlighted aspects of static electricity. Different methods of charging were used to generate charge on neutral objects and the action of electric forces, both attracting and repelling, were observed. Tomorrow, we'll look at what is behind the generation of electric forces - electric fields.
4/3/12
Electric Forces and Fields
B Block jumped into the arena of electric forces today. We tied up some loose ends from yesterday with a discussion of methods of charging neutral objects, then turned towards Coulomb's Law. We looked at the factors influencing the magnitude of electric forces (charge and distance) and how to assess the direction of a force on a single charge. We then layered on some complexity by looking at systems with multiple charges and how to determine the equilibrium position for a charge placed in a linear system. We'll go over these in class tomorrow, but don't forget to check out the videos in the last post for some help if you get stuck.
E and F Blocks had more practice with Coulomb's Law and how to work with multiple charges arranged in a line. A little time was given for students to challenge themselves by finding the net force on a charge where the neighboring charges are not on a nice, tidy line. Tomorrow, electric fields!
E Block reviewed their electric forces problems and more practice was given for those problem types, since vector operations are also going to come in to play with electric fields. Some folks didn't write down #3, so make sure you can solve for the equilibrium position of a -8μC charge placed between a 15 μC and a 3 μC charge that are 1.2 meters apart. The solutions for those problems (check yesterday's videos if you're still stuck):
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- -4 μC charge: 2.4 x 103 N along positive x-axis
- 7 μC charge: 2.2 x 103 N along negative x-axis
- -2 μ charge: 235 N along negative x-axis
- 1.86 x 10-5 N; 9.95° above negative x-axis
- 0.83 m from 15 μC charge
4/2/12
Third Video
Finally! The video for working with electric forces as vectors, when charges are not in a nice, tidy line:
Electric Forces Videos
Here's two videos. I've been trying for hours to get videos to upload and only managed to get these two to work. Somethings amiss in the great Internet today... (Note: videos can be rewound, if necessary)
For finding the net force for a charge in a line with other charges:
For finding the equilibrium position of a charge in a linear series of charges:
For finding the equilibrium position of a charge in a linear series of charges:
Electric Forces
B Block took time to go over their last test, Friday's lab and then jumped into the world of electrostatics. We discussed the property of charge and what being charged imparted on an object. The methods of generating charge on an object were described and the basic nature of electric forces was broached.
C, E and F Blocks took the electric forces ball and ran with it. Folks were reminded that electric forces were field forces, vectors and could both attract and repel, depending on the nature of the charges involved. We took time to look at Coulomb's Law for single pairs of charge and saw that electric forces are based on the magnitude of the charges and their separation distance (in an inverse-square relationship). We used Coulomb's Law to determine the size of the force between two charged particles, then extended that technique to the situation where more than two charges were present. For C and F Blocks, you can rest assured your charges will be in a line. E Block had to dig deeper into the vector nature of electric force and contend with particles that were not linearly arranged. They also had to determine the equilibrium position of a charge added to an established system. I'm trying to get a couple of videos uploaded to help you guys, but the host server is being a pain in the neck. Check back later, but if I can't get them posted... don't fret. Do your best - you do have all the necessary skills - and we'll go over them in class tomorrow.
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