Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electricity, AC and DC HELP

  1. Feb 18, 2004 #1
    electricity, AC and DC...HELP!!

    i hate science fair projects.... i need information. i am doing a project on Complete circuits and it is a cheap project. all i have are a few small light bulbs (one 6 volt, one 12 volt, and one 1.5 volt, and all are WAY old), a 6 volt battery, some wires with alligator clips, and a regular household light bulb. i understand that i cannot light up the regular household light bulb because it needs an AC current, and the current i am using is DC. But that is really all i have... i don't understand watts, volts, amps, coulombs, and all that! can someone help me? i have no idea where to go with this stupid project....

    thanks!

    :smile:
     
  2. jcsd
  3. Feb 18, 2004 #2

    dduardo

    User Avatar
    Staff Emeritus

    I moved this thread to electrical engineering. You'll probable get more help here.

    ----------

    Here are two was you can do this

    1. Get an AC wall plug and connect it to some lighbulbs. Use a rheostat (variable resistor) in various places in the circuit to show how resistence affects current.

    2. Build a DC to AC inverter. This can be a bit tricky, especially if you don't know much about electronics. There are various ways of going about building one, but the principle is basically the same. For a basic design you'll need some transistors, diodes, capacitors, resistors, and a transformer. Depending on the wattage, voltage and current you want to output, you'll need to pick the values for each component apporiately. I highly recommend doing some research on the internet about this or go to radio shack and get an electronics book

    Here is a simple version.

    http://www.aaroncake.net/circuits/inverter.htm

    Here is a more complicated version that has some voltage regulation circutry:

    http://www.interq.or.jp/japan/se-inoue/e_ckt8.htm

    If all else fails, you can always buy an inverter
     
    Last edited: Feb 19, 2004
  4. Feb 18, 2004 #3
    thanks DDuardo. i took a look at those sites. i will check out what you said also. thanks for the info! :smile:
     
  5. Feb 18, 2004 #4

    dlgoff

    User Avatar
    Science Advisor
    Gold Member

    Danae Legrow,

    This is a good idea but could be dangerous. Since the 120 volt potential from a household AC power receptical is measured relative to earth ground, becoming in contact with any exposed components could cause electrocution.

    Just wanted to make sure you understand.
     
  6. Feb 19, 2004 #5
    electrocution...

    electrocution would not be fun. thanks for informing me! i'm only in high school anyway, and probably won't be doing all that DDuardo said. thank you both!
     
  7. Feb 20, 2004 #6

    Cliff_J

    User Avatar
    Science Advisor

    Actually you can power the household light bulb with DC, BUT it has a high resistance so it would take many batteries to get enough voltage to overcome that resistance and get enough current to flow to heat it up and create light.

    That's all a light bulb does. You flow a certain amount of current through it, its resistance causes it to heat up and that heat produces light.

    The voltage on the bulb is indirectly telling you the resistance of the bulb, as per ohms law, since what it is telling you is how much voltage will be needed to allow enough current to flow to produce the amount of light it was designed to make.

    So you could wire the battery to the 6V bulb, it should be fairly bright. You could run it to the 12V bulb, it will not be as bright. Why?

    The household 120V bulb will be how bright? Why?

    The 1.5V bulb would burn out quickly. Why?

    If you use the variable resistor suggested above, why does adding resistance make the light dimmer?

    Simple safe experiments to demonstrate ohm's law. Borrow a multimeter if you want to verify the findings.

    Cliff
     
  8. Feb 20, 2004 #7

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Danae Legrow,

    I don't know what you intend to do (or are supposed to do) with those components. Can you tell us what you are trying to do?

    - Warren
     
  9. Feb 22, 2004 #8
    my project before and now

    thanks cliff! that was superfluously helpful! i shall consider those questions.

    chroot- this is and was my project-- i had a 6v battery, a 120v light, and some 12 gauge wire. i was going to run the circuit i was to create through some substances (conductors, semi-condustors, and things that weren't conductors). then i was going to write down which substances, when the circuit went through it, lit the bulb. then, come to find out, my wire was too large for the alligator clips i purchased. and the light bulb wasn't lighting up. i went to my grandfather and he cleared everything up, yet he changed my project. he gave me some light bulbs that he used when he worked on cars when he was younger. they are the smallest bulbs i have ever seen, and old, but they work. My grandfather told me why the 120v light wouldn't light: i was putting a direct current through to it, and it needed and Alternating current. although i think Cliff begs to differ... . So now, my project is a 6v battery, 4 little light bulbs (1.5v, 6v, and two 12v). i am going to try to explain why the battery i purchased would not light up 120v light bulb, using my grandfather's answer: thati needed AC instead of DC. i was going to then expound on the subject of AC/DC and then use volts and watts and amperes and stuff to explain what AC/DC was. then define what volt, watt, amperes are. that is all i have. i don't think that i have a very good hypothesis, enough to explain, or anything like that. my teacher wants us to expound on the topics we have picked and this is all i have. i am going to a friends house tomorrow to speak to her father ( her dad is an electrician ). he is going to help me actually put together what ineed and hopefully give me enough information to present maybe a little. but some more info may be nice. Cliff's questions were VERY helpful. good questions for me to look up and bring to my friends dad. but i hope that helps you Chroot. if this isn't enough, post again and say you need more, although i don't know what more you would need. thanks!:smile:
     
  10. Feb 22, 2004 #9

    chroot

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Cliff is correct. A 120V lightbulb will light just fine with DC, but not 6V DC. It would need more like 120V DC.

    - Warren
     
  11. Feb 22, 2004 #10

    Cliff_J

    User Avatar
    Science Advisor

    It would be responsible at this point to at least one important point:

    50 volts DC --OR-- 36 volts AC are considered LETHAL by some standards under the exact correct conditions. Be careful with anything near those levels.

    With a 6 volt battery and wires, you're fine, but you could always hook up an ignition coil from an old car and create 10,000 volts too. So we could easily leave experimenting with high voltage alone for now (good idea) and I'll just give you a quick history on why AC and higher voltages are common and DC and lower voltages are common associations.

    DC is most often found with batteries. A battery creates a voltage from a chemical reaction. This reaction only creates so much voltage, usually something like 1.5 volts. If you look at an really old car battery you can see the filling caps for each cell. Each cell only makes so much voltage, so many are placed in series to get the desired final voltage.

    AC is typically everything else, even though Edison orginally didn't want this. The reason Telsa's AC won over Edison's DC for powering our homes has an easy answer to it, and it has little to do with the electricity inside the home. Note we talk about 60 watt light bulbs, or 900 watt microwave ovens, and so on. A watt is a measurement of work performed, and a watt can come from DC the same as AC.

    So why does a light bulb, commonly remembered as Edison's invention by even school kids, powered by AC coming from Telsa partnered with Westinghouse near the turn of the century? Economics. Using AC allowed for economies of scale and lower prices that left DC behind.

    AC allows for a transformer to change voltage/current. The transformer is like a car transmission, in first gear you have lots of acceleration force but low speed, in high gear you have lots of speed but low acceleration force. The force is like voltage and the speed like current. Why is this important? Consider the Niagra Falls power plant. Not many people live near there, but NYC is close enough it can use that power. So some of that power needs to go a few hundred miles.

    But if you send a lot of current over a wire (like current through a light bulb) you create heat and lose electricity. But near a power plant they take the voltage and step it up to 500,000 volts with a transformer and send it over those big wires you see near some highways. Now the electricity travels hundreds of miles without making too much heat since its a lot of voltage but low current. After getting to the destination, another set of transformers steps that 500,000 volts back down to 100,000 and then 13,000 and then the 240 volts and 120 volts you have in your house. You see the transformer near your home because the electric company keeps the voltage high as long as it can to keep the losses in heat to a minimum.

    So AC wins because the transformer allows the electricity to be transmitted long distances with low losses. Which means just a few power plants can power large areas, very evident with the recent blackout in the northeast part of the US from OH to NY or California a few years back. Had Edison won, there would be a power plant every 5-10 blocks, and the rural population would still be lighting lanterns at night or using tons of batteries since it would cost too much to build a power plant for 20 people.

    Now, lets say you want to make high-voltage DC. Take an audio amplifier - its a pretty complicated device. A high-power car stereo amplifier takes the DC from the car battery, converts it to AC to run through a transformer to make a higher AC voltage, and then converts the transformer's AC output back into a high DC voltage, then turns that DC back into an AC signal that follows the music and sends that AC to the speakers. They don't seems like such different worlds anymore do they, AC and DC?

    Hope that helps clear up why AC is usually associated with high voltage and DC with low voltage, even though they are both able to do the same things and each have useful and unique features.

    Cliff
     
    Last edited: Feb 22, 2004
  12. Feb 23, 2004 #11
    cliff, that was awesome!

    thank you so much clff for all that wonderful information! i just got home from my friends dad's house and he expounded a little on the power lines thing, but you were awesome! thanks! i will use that in my report.

    -danae :smile:

    boy am i tired... haha [zz)]
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Electricity, AC and DC HELP
  1. Help with AC and DC (Replies: 15)

  2. Help need Fo DC ANd AC (Replies: 1)

Loading...