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

Electrical B.S.ing

  1. Nov 17, 2004 #1
    I'm for the most part an electrical newbie, although I have made a guitar amp. I am the type of person who doesn't like to do things when I don't understand what I'm doing. I was wondering how many electrical hobbyists/engineers actually understand electronics, and how many are just working with numbers, symbols, and formulas. Throughout the building of my amp I asked my physics teacher(he's the best I have, I'm in highschool) about how certain components work, and what amperage and voltage really mean. I have a ton of questions, if anyone could direct me to a site that could explain these things I would be grateful. I understand the flow of electricity and stuff, but, for example, if you change the resistance in a circuit, does that also change the current or the voltage? And do resistors really just turn energy into heat, like my teacher said, or do the just restrict it's flow?
  2. jcsd
  3. Nov 17, 2004 #2


    User Avatar
    Science Advisor
    Homework Helper

    I might try getting a subscription to something like Nuts & Volts.

    >And do resistors really just turn energy into heat, like my teacher said, or do the just restrict it's flow?
    That is how resistors work.
    The point of having one in a circuit might be to restrict the flow of energy.
    Or the point might be to create a voltage divider where energy flow is not important.
    Or some other use.
    Also there are ways to restrict energy flow without using resistors.
  4. Nov 18, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Last edited by a moderator: Apr 21, 2017
  5. Nov 18, 2004 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    What you call voltage (more properly known as potential difference) is, loosely speaking, a measure of how much "force" is applied to electrons. The more force you apply, the more movement you will produce. The movement of electrons is amperage (more properly known as current).

    Both units can be easily understood by first understanding the meaning of a "coulomb" of charge. A coulomb of charge is the charge on a specific number of electrons -- approximately 6.25 x 1018 of them.

    An ampere is a unit of current; one ampere is defined as one coulomb of charge moving past a given point in one second. It's analogous to the flow of water in a pipe; a larger amount of water moving past a given point in a given time is a larger flow.

    A volt is the same unit as a joule per coulomb; if you subject a coulomb of charge to a potential difference of one volt, the electrons (or protons, or whatever) bearing that charge will gain one joule of energy when moving from the high potential to the low. In much the same way, a ton of bricks will gain a specific amount of energy when released from the top of a building and allowed to move from a high gravitational potential to a low one.

    - Warren
  6. Nov 18, 2004 #5
    And to answer your question regarding the resistance changing in a circuit, we will look at Ohm's Law.

    E = IR

    E = Electric Potential (Voltage) (Volts)
    I = Current (Amps)
    R = Resistance (Ohms)

    This shows that Voltage is directly proportional to both current and resistance. If you raise I and/or R, E raises as well.

    So, for your question above, if you increase the resistance of a circuit and hold the current constant, the voltage will increase.
  7. Aug 12, 2005 #6
    Something isn't quite right here....a volt IS the same unit as joule per sec. Also, when 1 coulomb of charge passes through 1 volt of potential difference it does in fact gain energy, since even though the distance of separation between 2 charges decreases, the E-field increases at a greater rate due to the decrease in separation distance (e-field is inversely proportional to distance). Integrate E*dl for a given e-field and you'll see that potential is inversely proportional to distance, which means that as distance decreases as the charges passes through the potential difference, the energy will increase.

    However, gravitational potential energy is not a direct analogy to this because gravitational force is constant (constant accelleration for a given mass) unlike electric field, which varies inversely with the square of the distance. So, if you decrease the height by dropping an object, you are going to decrease the GPE. for electrical potential, this is not the case, since e-field strength increases at a higher rate than distance decreases when a charge passes though a potential difference.

    So, electrical potential and gravitational potential are sort of reverses of one another, since gravitational force is constant for a given mass as distance varies , whereas electric force varies for a given charge as distance varies. T
    Last edited: Aug 12, 2005
  8. Aug 12, 2005 #7
    This is one of my favorite references for electrical questions. Bill breaks the definitions down into precise terms and his explanation of how transistors work is a heck of a lot better than what I was originally taught.

    I know a few hobbyists who don't have a real understanding of the principles behind the electronics they play with... as for myself, I've been taught electronics three times and I'm ready to go learn it again, for a degree this time. :rolleyes:
    Last edited: Aug 12, 2005
  9. Aug 12, 2005 #8


    User Avatar

    Staff: Mentor

    Last edited by a moderator: May 2, 2017
  10. Aug 14, 2005 #9
    I would like to believe that MOST electrical engineers have a thorough understanding of the concepts they apply everyday. However, considering how many engineering curricula are run, it wouldn't surprise me if many engineers really didn't understand many of the underlying concepts. Many engineering curricula are like bootcamps, where little deep thought is required regarding the underlying concepts, and one can simply do a hundred similar engineering problems to prepare for an exam and they will do fine, and students get through their entire degree program this way. Often, students rely on their memory. and not on their understanding.

    Plus, engineering professors get TOO mathematical when explaining things, and textbooks are often the same. This means that the conceptual aspects are overlooked, and students BELIEVE they have the right idea of a concept, but they are in fact thinking of the concepts incorrectly. This is especially the case in electrical engineering, where the concepts are often very abstract.
  11. Aug 17, 2005 #10
    Actually, Warren is exactly correct.

    Joules/sec = Watts or Power. Volts x Amps = Watts;

    Volts = Joules/Coulomb, Amps = Coulombs/second.

    Coulombs/second is intuitive as a flow of charge.

    Joules/Coulomb is less obvious but it is the amount of
    potential energy contained in a coulomb of charge
    which is held against a 1 volt potential.

    Power is Energy/time, so pushing a coulomb of charge
    through a one volt potential in one second is the same
    as pushing an object against one Newton of force through
    one meter in a second.

    They are both one Watt.
    Last edited: Aug 17, 2005
  12. Aug 17, 2005 #11
    oops. I meant a volt is a joule per coulomb. During that first paragraph I was agreeing with what he said. The second part of the post I was disagreeing when he related electrical potential with gravitational potential. Some of what he said here is incorrect.
    Last edited: Aug 17, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Electrical B.S.ing
  1. Electric Signals (Replies: 16)

  2. Electrical services (Replies: 85)

  3. Recycling electricity (Replies: 8)