Archive for experiment

How to Get Far Without a Car

Some of you readers may recall when I made a pledge to sell my car in order to green my travel around the city.  It’s been more than three years now, and I’m happy to report that I haven’t died from lack of access to basic goods yet, so clearly, it IS possible to make work, even in a city as sprawling as Los Angeles.  It’s fairly easy to trade in the frustrations of driving, paying for inevitable parking tickets, car insurance, gas, crazy-driver door dings and side view mirrors lopped off by passing cars for the peace of mind that comes with regular exercise and time spent enjoying LA’s incredible outdoor clime.  Of course it does have a few drawbacks, the greatest of which being that it’s harder to get out of town to places which are far enough away to necessitate a car but not far enough to be serviced by the Greyhounds and Metrolink trains of the world.  There are a few strategies I’ve employed over time to make it work without feeling deprived.

First, I took a good look at the places I travel in a normal day.  Since I work “from home” but live off-grid without power, my primary need in the work department is occasional access to an outlet to recharge the computer and internet to post stuff like this, converse with clients, etc.  About a year and a half back, I purchased a netbook with a seven hour battery life.  Best investment ever! This means that I only have to find an outlet for an hour or so daily to have my portable office up and running for more hours than I can practically stare at a screen.  So I hit a local coffee shop each morning, sip tea, upload posts, and download relevant research for the next edition or client.  The mile or two walk to and from the shop each morning gives me a chance to start my day outside, practicing walking meditation (a post on this coming soon!) and organizing in my head what I need to accomplish.  As a photographer, I carry my camera with me everywhere I go, and this walk also allows me to get interesting shots in the golden light of early morning before most people wake up.  What started as an obligation to get to a destination has actually become one of my favorite daily activities!

Over time, I’ve discovered local alternatives to my daily purchases.  The other day, I found the best little pupuseria while walking by on an errand, saving me a bus trip across town to my other favorite streetside vendor.  How’s that for ultra-localizing life!  Many people drive all over creation going to stores that they are used to frequenting when there exist alternatives right within their own communities.  By shopping locally, not only will you save frustration and gas/insurance money, you might also get to know your local business owners better, which helps build stronger community ties.  Of course, supporting your local Best Buy over a family run electronics shop just because it’s down the road isn’t necessarily what I’m talking about, but even franchise businesses are run by individual owners who may be from your community.  Take the time to ask, it can often lead to an enlightening conversation.

When needing to get out further than walkable distance, I can get most places for $3, the current price of a round trip bus or metro ticket in these parts.  Sure, it takes about fifteen minutes to walk to or from the metro station, but I simply view it all as exercise and think about the money I save by not having a gym membership while I walk.  If the destination lies off a main bus or metro line, then I might ride my bike to the station, which cuts the travel time down even more.

In order to head out of town/city limits, which is an occasional necessity given my other-other day job as a treasure hunter, I’ve had good luck by posting on Craigslist for someone to drive to a given destination, even one off the beaten path.  Usually it costs me gas money and the price of lunch, maybe an honorary token payment, far less than it would to rent a car for the day and I don’t even have to drive.  (yet another option is signing up for a shared-car service such as Zipcar, which I’ll cover in an upcoming post)  There are several rideshare sites which can be used in similar fashion, especially if one is not tied to a particular moment of travel and can be a little flexible.  Of course as a woman I am careful about this, bringing a buddy with me to share the ride and always being on top of knowing the exact directions to where I’m heading.  You can also run a classified ad for people to pick up items from further locales and deliver them to you for a nominal charge if they are headed some direction anyway.  Given the state of public transport here expanded by an additional biking radius, both this and the ride for hire scenario are rarely utilized but useful tools to have in the arsenal.

One final thing that I’d like to mention here is that of motivation.  If you’re going to be walking or biking, why not reward yourself for putting in miles toward the sustainable cause? There are many websites that let you track your exercise miles over time and provide like-minded communities for motivation and friendly competition.  I started using dailymile.com a few months back to log miles walked in order to see how much gas I would theoretically save each month by not driving.  It nicely computes my calories burned, keeps track of the amount of gas I’ve saved by not driving, and even tells me other fun stats like how many donuts I can now afford to eat after all that walking!  Though the site is primarily designed for athletes who are training for things to share inspirational workout routes, it serves well too as a general tracker of miles logged, featuring interactive route maps which calculate your mileage based upon the path you draw on a Google map.  One of my favorite features of the site is the challenge page, where you can sign up to try and complete a certain number of miles or hours spent exercising during a given time span in friendly competition with other athletes on the site.

The luxurious abode that is Trimpi Shelter.

Last Thanksgiving I signed up there for a virtual Appalachian Trail hike, in which walkers try to log the 2179 miles of the AT within a year’s time.  I use my distance data from the site (it keeps track of which types of exercise qualify, in this case walking and hiking) and compare it to a distance map of the trail to see where I am on a given day.  Today, two and a half months after starting out my “hike”, I’ve walked through Georgia, North Carolina, Tennessee, and am venturing up through southern Virginia toward the Trimpi Shelter, pictured above, where I will virtually slumber this evening.  Right now things are on track to finish the trail with a few weeks to spare, which at the necessary rate of 5.5 miles daily is no small feat!  By looking up each county I travel through on Wikipedia and reading about what the areas are known for (the Trimpi shelter is in Grayson County, VA, mountainous home to several annual bluegrass and fiddle music festivals and a yearly through-hiker festival which celebrates those trying to complete the AT), my daily walking chores have changed from a simple necessity into an exciting and educational activity which feels more like a vacation.

The location of the Trimpi shelter along the Appalachian Trail.

Well, those are a couple things I have found useful.  What strategies do you employ to cut down on extraneous daily travel? How have they worked for you?

Comments (2) »

Resolutions for 2009

It’s that time of year again… time to dust off last year’s resolutions and slap a new title on ’em.  No, of course not!  To me, the best thing about writing down resolutions is revisiting them in the far future as a sort of diary of where you were in life at that moment. I’ve gone every way – make one and stick to it, make fifty and try to hit as many as possible, and pretty much everything in between.  In doing so, I’ve hit on a system that seems to work pretty well in terms of actual achievement:  these days, I make as many as will fit on the front of one piece of paper, then post it on the wall of my clothes closet.  In the mix are at least two very easy things to achieve, at least one hard one, and at least one long-term carry over from years past.  Oh, yeah, and ushering in world peace, which I can only hope will be achieved in my little lifetime!

So what does 2009 bring? The Solarious experiment has been going strong for ten months now, making this the first Jan 01 I’ve encountered here.  From a starting posting frenzy, posting has fallen into a few lulls as life business crowded its way into the forefront.  So my first resolution is to find a comfortable posting schedule that will allow you to get all the latest info while still keeping food on my table.  Isn’t that the great game of life anyway? But on to the good stuff… what’s new here at Solarious!

Interviews Galore!

I resolve to make this site a premier destination for people who are looking to reduce their burden on the planet.  I will introduce a monthly interview series with political and environmental leaders and with people who are making great changes in their own lifestyles so that you can hear firsthand how easy taking the green path can be.  I’ll also be profiling green (and not so green) cities and communities to show you real-world examples of places taking action against global warming and other such monsters.  If there’s someone you’ve been dying to hear from, let me know, and I’ll try to make it happen.

Second, I will be introducing an organic series discussing gardening tips, food purchasing tips, home decorating ideas and interesting low-cost ways to bring organic products into your home.  Check back every few weeks for a new installment.

I’ve been reading (and reviewing) books like crazy this year. And until the library runs out of titles, you can expect more of the same in the coming months.  Look out for an improved rating system which helps define which titles are good for general info versus one which give you practical tips you can implement now, and also a library page which will allow you to search reviews by topic.

Class Time!

Class Time!

The solar power class is up and running now (check out the Photovoltaic class page), but again, look for improvements such as a searchable list of places offering photovoltaic classes around the country and an expansion into wind and other renewable technology theories.  I’ll also be adding a practical projects gallery, complete with photos of completed installations and a rating system denoting how difficult each was to complete and how well it works. The other back pages will be getting more updating love too!

The summer sunshine seems like a distant memory right now after a week of rain, but the solar cooking section will also be getting its own page, complete with recipes and a larger variety of cooker and dehydrator projects for you to complete.  I’m hoping to get a few “beta testers” and a rating system for the dishes as well, so that you can get a better idea of how things taste.  My cats will be so disappointed to have their job outsourced, but sacrifices must be made in the name of science, no?

Thats a Lotta Carbon!

That's a Lotta Carbon!

I’ve also made a personal commitment to make this blog carbon neutral.  Every day, I will offset the carbon used while plugging in to post. Because there’s nothing I want less than to make MORE pollution!  If you want to do the same, check out my last post, “making you computer carbon neutral” for some tips on reducing your digital burden.

And the super long-term goal? Well, like many of you, I’d like to completely cut the power lines in life.  Having no power at home and having sold the car as outlined months ago, I’m already pretty far along with that goal… but until I get off my butt and install some real solar power, I’m still internet cafeing it (which entails eating some pretty long miles-to-plate meals, no doubt) and using municipal water for basic human needs.  So, those activities are on the chopping block as I look for ways to cut back even further.  Teaching people about the joys of alternative energy is one way I can reduce this burden without actually making life any more spartan. Every time you implement something you learned here or pass it along to someone else who does, the total planetary energy load is reduced by that much, which makes me so very happy.  So in closing, I ask you this: if you see something of interest here and implement it, share your experience with the rest of us or at the very least, tell your friends! Together, we can make 2009 the tipping point for renewable energy and sustainable living to bring both into the mainstream for a brighter, cleaner future. 

Blessings to all of you, and thank you for a wonderful year here at Solarious.

Leave a comment »

Thanks Everyone!

Just a quick thank you to all you wonderful readers out there: You helped make Solarious one of WordPress’ Fastest Growing blogs for the month of September 2008!  Thousands of people have followed my journey and hopefully started or continued on their own.  To each and every one of you, I salute you.  Together, we will reshape the future.  Thanks again!

Leave a comment »

Find Balance (or it will find you!)

What is it about balance, the great equalizer, that makes it so circumspect a teacher? In life I have always had a tendency to go overboard on things… not dangerously or nuttily so (hopefully!) but if I decide that nothing beats peach ice cream, well, three or four pounds of that stuff might make it into the shopping basket!   Which is where I find myself now: having discovered all of a sudden that there IS a corner fit to raise a few plants in the confines of my current tiny living space, I proceeded to buy about seven pots and plant all sorts of seeds that I’ve collected over the past few years while waiting for a spot to garden again.

I was feeling a little guilty about taking up so much available real estate with pots.  However, so busy was I watching the pretty little seedlings push up out of the soil and grow stouter and sturdier with each passing day that I neglected to notice that my kittens are also growing each day, and getting into more and more mischief along the way.  So it was that the other night there occurred a tragic plant homicidal incident that I knew was coming somewhere in the back of my head.  The kittens, having recently discovered the joy of heights, have taken to sleeping in my plant pots, tipping them wantonly, and chewing off the young greens.  Every morning, I awake to a new field of floral carnage and (literally!) soiled carpet. My plants have become refugees in their own biosphere, moving every few hours to places where they can be guarded against feline attack.  One kitten in particular has decided that nothing beats an aromatherapy nap in my basil, rosemary, and mint, and all three are currently trying to adjust to the daily stomp-down.  Not that I blame him, it DOES smell good there!  But at least it forced me to redecide on an appropriate amount of space to devote to growing, since several pots required replanting or retirement.  Ah, balance, the great teacher.

Growing an herb garden is shockingly easy, as herbs generally tolerate spottier care than other plants and they smell so wonderful along the way.  Of course, each has its own desired care prescription (planting mint, a water lover, and sage or lavender (drought lovers) together in the same pot might not be the best idea, unless you like seriously wilted sage!), and likes differing amounts of light.  But in general, all will stand up to more abuse than a “pretty flower” plant.  (If your growing conditions are seriously strenuous, consider cactus gardening.  Mine have survived and even thrived in trying conditions, and they require little to no water except when flowering.)  An added bonus of a kitchen garden is that fewer pests will be able to find your tender plants and unleash their destructive forces.  Of course, as I’ve found, you might have bigger pests to deal with!  Also, you’ll be able to enjoy fresh herbs for cooking year-round.  Basil, mint, lavender, wild strawberries, rosemary, ginger, and garlic are reliable performers for the beginning gardener.  To find out more about planting an herb garden, see the WikiHow article link in the gardening section of the links panel.  In no time, you’ll be kicking those packaged 1500-mile-to-plate supermarket herbs to the curb.

Comments (1) »

Getting the Mail

Reducing your life footprint on the earth sometimes means making a few more… by walking instead of driving to local destinations.

Having sold the car a few months back as part of this solarious experiment, I’ve been hoofing it all over the city this summer. It’s been great for getting a tan, and also a refreshing way to view the neighborhoods in my area. A good walking street does not necessarily mean the same for driving, and since you have plenty of time to examine things as you go by, you’ll probably find yourself seeing details you never noticed right in your own stretch of town. I use the time to look for edible and native plants along the street… in Los Angeles, there is an old law that states any tree or plant that overhangs the sidewalk is fair game for harvesting by the general public (see FallenFruit.org, a great website complete with “Fruit maps” and a commendable mission statement for more on this). Yesterday, as I trekked to get my mail from the post office, a stretch of about 1 3/4 miles that I used to cover by car in about 5 minutes without more thought or notice than to curse the traffic gods, I recorded the following:

Walking down Santa Monica Blvd, sharing the sidewalk with transvestite hookers and average Joe and Jane shoppers peacefully co-mingling around large retail storefronts, I turn back onto a neighborhood street once known as an artists’ mecca, but which is now a darkly comical mix of homeless people camping near the lawns of middle income family homes. There are ample opportunities for herb stalking here, which occupies me for the remainder of the block (a funny thing about LA is that regardless of its immense size, the cultural landscape changes drastically every couple of blocks, kind of like a permanent Olympic Village).

I make my way to Melrose Ave, past a sea of tourists waiting in a never-ending line for Pinks Hotdogs, and past the local halfway house for adults with developmental disabilities which shares its corner with one of the most popular Cuban restaurants in town. As I walk by, the halfway house residents are watching the arrival of a Hollywood celebutante and her entourage at the restaurant, who, needless to say, are not watching those watching them. Melrose is awash with foreigners who haven’t yet heard about the street’s decline and think that they’ll find the next hot designer outfit there. These days, you’re more likely to find a ten dollar clubbing outfit or a glass bong, though a few brave designers have shops there still. Mixing with the exotic foreigners’ accents are the rough voices of immortal punk rockers, the giggles of wannabe high school hipsters, and the rolling grumbles of Persian and Asian store owners who still work the sidewalks attracting customers. Turning off Melrose, I walk down the alley through an open air art museum, courtesy of the talented taggers and spray can artists who’ve made the alleys their gallery for years, and hopefully for many more to come. This is one of my favorite spots in the city, and I linger for a few moments to appreciate the ever-changing canvas.

Beyond there is another neighborhood, this one the domain of the local Orthodox Jewish population, where men in Yarmulkas drive nice cars (except on Shabats) and women in long black skirts push double wide strollers down the sidewalks. This is another foraging mecca, lots of date palms and fruit trees, undoubtedly because the second-generation families who live there still appreciate the historic reality of food shortages and self-sufficiency. The houses themselves are historic craft services houses from the golden days of Hollywood, each with their own character and story.

Turning onto Beverly Blvd, I start to notice Ferraris and Porsches parked street-side, indicating I’m now in the realm of the hipster designers. Trendy cafes and coffeehouses are interspersed with interior design firms and Fashion Week designer boutiques. Writers peer intensely at passers by from behind their laptops and eavesdrop on actors who gather to share “I’m too cool” party tales with other actors with whom they are, no doubt, too cool to be hanging out. Finally, I pass the local public park, a haven for youth sports leagues, middle aged joggers, and boheme-chic refugees from CBS Studios’ resident neighborhood actor population and the renowned Farmer’s Market (which is now more like a shopping mall) just beyond. Inside the park’s entrance stands a largely ignored Holocaust monument to those who died in the great war and the remnants of an old amphitheater that, despite being in the heart of thespian territory, today only serves as a frisbee park for local dogs and the meeting spot for several Hollywood fitness boot camps.

In twenty minutes, I feel like an ambassador at the United Nations, having traveled half the globe without ever leaving town! As a bonus, I’ve gathered enough seeds from passing plants to start a respectable guerrilla garden somewhere, got a good workout, and it took no fossil fuels to get to my destination, save whatever was used in making the rubber soles of my shoes. Most importantly, I got to interact with my neighborhood on a personal level, rather than simply staring out the window at a traffic light.

Is there somewhere local that you generally drive that would be a good candidate for a walk? If time is a luxury, then treat yourself to a little jaunt through your local world. Picking a regularly scheduled destination you already frequent will help encourage you to ditch the car and get out more often than simply saying “I will go for more walks”, at least if the shattered remains of many new years resolutions are any indication. When you do decide to hoof it, keep a mental trip journal and post your best tales here! See you on the street~

Leave a comment »

Solar Power Class: Formulae Roundup

Okay, so back to the classroom, while it’s fresh on your mind. Yesterday we talked about Kirchoff’s Laws, as well as a few other formulas that you’ll use when trying to figure out your electrical generation setup and capacity. To review, here’s a listing of formulas:

Voltage = “Electromotive Force” = E
Current = “Amperes” = I
Resistance = “Ohms” Ω = R
Power = “Watts” = P

Ohm’s Law (for DC power): voltage = current * resistance ( E = I * R ),
power = current * voltage ( P = I * E )

Total Circuit Resistance: SERIES: Rt = R1 + R2 + … + Rn
PARALLEL: 1/Rt = 1/R1 + 1/R2 + … + 1/Rn

Voltage Divider Formula (Series): Erx = Et ( Rx / Rt ) (solve for resistor “x”)
Current Divider Formula (Parallel): Irx = It ( Rt / Rx ) (solve for resistor “x”)

Kirchoff’s Voltage Law (Series): Et – E1 – E2 – … – En = 0 (circuit w/ “n” resistors)
Kirchoff’s Current Law (Parallel): It – I1 – I2 – … – In = 0 (circuit w/ “n” resistors)

Whoa, boy, that’s a lot of formulas! Using these, you can pretty much figure out whatever you want about a simple series or parallel circuit. Of course, the circuits designed for power generation are rarely simple like the above, but we’ll get to that in a second!

So now that you’ve beat these formulas in your head, how do you use them? Here’s a sample problem:

“A 220V series circuit has three resistors. The first has a resistance of 25Ω, the second has a resistance of 50Ω, and the third has a resistance of 35Ω. What is the current and resistance of the circuit, and what is the voltage drop across each resistor? How much power will it produce?”

First, you diagram everything to see what you’re working with. You see that it’s a series circuit, which means that the current is common and the total resistance is the sum of all the partial resistances.

Rt = 25Ω + 50Ω + 35Ω = 110Ω

and since E = I * R, 220v = I * 110Ω, or I = 220/110 = 2 amps.

So now you know the voltage (220 V), the resistance (110 Ω), and the current (2 amps). To figure out the power produced, you simply use Ohm’s Law, (P = I * E), or P = 220 V * 2 amps = 440 watts. We’ll add that to the list: power (440 W).

The final part of the work is to figure out the voltage drops across the circuit at each resistor. This will require the voltage divider formula, since it’s a series circuit. ( Ex = Et ( Rx / Rt ) )

Here are the values plugged in for resistor 1: Er1 = 220V ( 25Ω / 110Ω ) = 50V.
Here are the values plugged in for resistor 2: Er2 = 220V ( 50Ω / 110Ω ) = 100V.
Here are the values plugged in for resistor 2: Er3 = 220V ( 35Ω / 110Ω ) = 70V.

You can check your work on this by adding all the voltage drops together: they should equal the voltage given in the problem: 50V + 100V + 70V = 220V. Good! Now for extra credit you can figure out the power produced at each resistor by using your power formula and the voltage and resistance of each resistor in the circuit. If you do, post your answer in the comments section!

This is basically the same process as for parallel circuits. Let’s use the same problem as above, but now the circuit is hooked up in parallel:

In this case, to get total resistance, you use the formula 1/Rt = 1/R1 + 1/R2 + 1/R3. This looks scarier than it is. to get a reciprocal (one divided by a number) on a calculator, you simply plug in the number, hit the divided by sign, then the equals sign. The calculator will do all the dirty work for you, but you should try doing them in your head sometimes, ’cause you never know when the calculator might stop working when you need to figure something out! So:

1/Rt = 1/25Ω + 1/50Ω + 1/35Ω = .04 + .02 + 0.0286 = 0.0886

This is the reciprocal of the total resistance (this is also called the “conductance”), so we take the reciprocal of this and get a total resistance: 11.287Ω. A total resistance of less than each of the parts? Yes, this example illustrates two things about parallel circuits: first, the numbers are rarely as “pretty” as in series circuits. Secondly, the total resistance of a parallel circuit is always less than the lowest partial resistance. If it’s not, then you calculated something incorrectly.

So now, as before, we know the voltage (220V) and the resistance (11.287Ω). To figure out the total current, we use Ohm’s Law ( E = I * R ): 220V = I * 11.287Ω so I = 19.49 amps. You can now easily figure out the power produced: P = 19.49A * 220V = 4287.8 watts of power (or 4.3 kW).

Using the same resistors and voltage, you’re generating more than ten times the power by hooking things up in parallel!

Rounding out the lesson, you’re now trying to figure out the current drop across the resistors (remember, in a parallel circuit, current is divided, not voltage). Use the Current Divider Formula: Irx = It ( Rt / Rx )

Here are the values plugged in for the first resistor: Ir1 = 19.49A ( 11.28Ω / 25Ω ) = 8.794 A.
Here are the values plugged in for the second resistor: Ir2 = 19.49A ( 11.28Ω / 50Ω ) = 4.397 A.
Here are the values plugged in for the third resistor: Ir3 = 19.49A ( 11.28Ω / 35Ω ) = 6.281 A.

To check your numbers, use Kirchoff’s Current Law, and add up the current drops:
8.794 A + 4.397 A + 6.281 A = 19.472 A, which is the same as above, save my rounding. This is why it’s important to keep numbers true to the highest number of decimal places you can… your work will be that much more accurate.

Again, if you want to figure out the power available at any point, use the same process as for the series circuit.

Congratulations! You’ve now mastered simple series and parallel circuits. That’s a lot to know. Next time, we’ll take a look at how to deal with more complex circuits, like the ones you might encounter in your alternative energy generating system, and also talk about why all this math is important to you when all you want to do is drop off the grid and tune out. I found that this stuff didn’t really cement in my head until I tried figuring out practical problems with them, so I’d recommend you do a little practice session, perhaps using the problems found at Open DNS: Ohm’s Law Practice 1, and Ohm’s Law Practice 2. Or try this site if you like to “play and learn”: Ohm’s Law Battleship Game, where your shots won’t land unless you can solve some problems along the way. See you next time, captain!

Comments (1) »

Solar Power Class: Kirchoff’s Laws

Whew! It’s been a busy couple of weeks in my photo-voltaic class. I was starting to fear that I’d have to take a math class to keep up with all the formulas! When I posted the first week’s lesson, I realized later that I’d given out misinformation, which is the danger of posting about something you don’t yet understand! So, from this point out, I’ll just post the lessons after I’ve been tested in the contents, that way you’re always getting the information someone has TOLD me I understand. Since we had a test this past weekend, here’s a new dose of mathematical fun!

This week: Kirchoff’s Laws. Last time, I discussed Ohm’s Law of DC power, which interrelated voltage, current, amperage, and power, and provided several formulas you can use to figure out any of the above for a circuit. If you’d like to review, check out the original post here. Now, let me repeat a few pertinent facts: a series circuit is when you basically hook everything up in a big loop, positive end to negative end in a chain. See the diagram below:

A parallel circuit is one in which the positive and negative ends are “shunted” together (parallel circuits are sometimes called shunts) creating a ladder effect. Again, see the diagram below:

Series circuits are called voltage divider circuits, because though a common current flows across the wire, at each stop along the way, voltage is dropped. These are two important concepts: 1. current is common. 2. voltage is divided along the circuit. Parallel circuits are the opposite. Though a common voltage flows through all the wires, the current is divided between the different potential paths. Therefore, in a parallel circuit, 1. voltage is common, and 2. current is divided along the circuit. Series circuits are called “voltage dividers” and parallel circuits are called “current dividers”. VERY IMPORTANT is you want to know how to manipulate these circuits later on.

There are even two formulae which will help you to calculate a voltage or current at any particular point along a circuit. Say you have three resistors along your circuit. In a series circuit, a voltage divider, if you want to know the voltage of resistor “b”, you would use the voltage divider formula: Erb = Et (Rb/Rt), where t represents total and Er is the voltage drop. Here’s an example:

In a series circuit with a total resistance of 100 Ohms, and a voltage of 120V, resistor b has a resistance of 25 Ohms. The total voltage drop across resistor b would be:

Erb = 120 v ( 25 Ohms / 100 Ohms ) = 30 V

Now, if you aren’t sure what the resistance of a particular resistor on the circuit is, then Kirchoff’s Law of Voltage (for series circuits only!) comes into play. His law states that the total voltage minus the voltage of each resistor, etc on the circuit will always equal zero. In other words, the Total Voltage equals the sums of all the voltage drops along the path. Here’s the official equation: Et – E1 – E2 – … – En = 0, where the circuit has n resistors. So if you know that one resistor has a voltage drop of 25 v and the third has a voltage drop of 50 v, and the total voltage is 130 v, then 130 – 25 – E2 – 50 = 0, and E2 = 55 v. Got it?

Now, on to parallel circuits, ones you’ll see a lot of in battery configurations. Because parallel circuits are current dividers, they need a separate formula for figuring out current drops around the circuit. This is called the Current Divider Formula (using Current at Resistor b): Ib = It ( Rt / Rb ). As with the voltages of a series circuit, if you need to know the current drop at a particular point, Kirchoff had a law for that, too. It’s called Kirchoff’s Current Law (for parallel circuits), and it states that the total current minus the current drops along the way, equals zero. So It – I1 – I2 – … – In = 0, where the circuit has n resistors.

Now, this is a LOT of information to absorb, especially in practice, so let me stop here for now, and we’ll pick up here tomorrow with the rest of the lesson. It seems like way too formulas to ever be useful, but once you get to solving practical equations with them, it’s not too bad. But let’s save that for the next lesson, sleep on it, and I’ll see you in class tomorrow~

Comments (2) »

%d bloggers like this: