Student Ramuel Mendoza Raagas for Teaching Fellow Ronald Newburgh, Ph.D.

Physics E-1b
Pre-Lab for Experiment #2:
Direct Current Circuits
Spring Term 2003
Submitted June 4, 2003
  1. Hypothesis:

    In physics, zero is no mere empty basket. Invented by Indian civilization, the zero is an all-important, not-merely-trivial number which opens new worlds, even perhaps more so than infinity itself.

    If the greatest ENglish bard ever wrote rthe masterpiece Much Ado About Nothing, it might be quite a lucrative project to work on a layman's science book by the title Much Ado about Zero. Zero, in, our universe is a broad governing force.

    Electrical circuits are often quite circuitous means, of ideally, boiling down to zero. When circuits progress into more compound concatenations, we often can resort to looking for the zero that will be our guiding light. Well, it's not just in direct current circuits, even in the pedagogically prior topic of electrostatics, the zero turns up like a rising sun often enough. Even, later down in the topic of electomagnetism where currents fuse the curl, gradient and derivate terms of magnetic field B and Electric field E into common-time-space equations, the ubiquitous zero will help out in eliminating one component of terms from an adjacent one, making the calculations of line and surface integrals less cumbersome, and, in fact, more manageable.

    In electrostatics, and the entirely separate phenomenon of magnetostatics (Yes, without current, which would serve as a common household, electricty and magnetism are separate individuals each minding its own pool of properties.) it was Maxwell's equations that gave us our zero's. Electrostatics has zero as

    We will look into two of Kirchoff's most fundamental rules: the loop and junction rules.

  2. Procedure

      1. multimeter: Whereas a galvanometer may be either a voltmeter or an ammeter, the multimeter may be not just either of that but even an ohm-meter (a measurer of resistance) . The voltmeter and ammeter modes call for the user to ensure adequate resistance in between the left and right points of clamping. Bare wire must not be all there is. The conductivity of such would wreak such a havoc current no longer in the realm of mere analysis-useful error, but in the quagmire of disastrous equpiment damage. The difference between the ohm-meter mode of operation to either voltmeter or ammeter mode is that potential difference is not to be involved in our measuring the passive element (such as an isolated resistor plucked apart from any circuit) of our interest.
    • breadboard
        three breadboard components
      1. lightbulbs
      2. several resistors, a number of which are identical with each other
    • gator clips to clamp on bus bar (which serves as ground) as well as right before and after the voltage drops IR, Q/C and Ld2Q/dt2 cause by the above trio of breadboard components

    All in all, we will build eight circuits with switches. This experiment has two parts: the first qualitative, the second quantitative. The qualitative part establishes equality and inequality relations in current flow (as evidenced by light bulb glow, which we need not quantify in terms of candelas). Part one's four circuits will have each between one and three light bulbs. Part two will also have us concerned with magnitude of current (directional flow of current as becomes a task in itself in more complex di-battery Kirchoof joint-loop circuits will not yet be a concern). This time, however, we will not settle with ascertaining current at a glance,

    4. Preliminary Answers to Bold Questions

    1. There are two conductors on the outside of a light bulb. There is only one insulator on the outside of the bulb.
    2. Two wires connect to the filament which glows, giving the light we desire, but even more of the heat we did not really care to get out of the bulb. Each of these goes to a different point of contact.
    3. The light bulb socket

    4. The same result will not be achieved if the direction of current is reversed.

    5. A = B < C
    Both these first two circuits, I guess, are series circuits, although seems more emphatically so a series circuit compared to the first, which has only one Rload item in series with the voltage source and switch. Even if A is closer to the battery's sequence of conventional flow, it cannot grab more current than the bulb B which follows it, because the principle of current flow for passive elements connected in series would have them experience the same amount of current. What do the brightness questions 5, 9 and 14 in this lab involve? Power or current? Which of the two? That light bulbs (i.e., incandescent) are marketed with power in Watts ratings emphatically indicated might lead to the intuition that the greater the Wattage of a given bulb, the brighter would be its output of light (and greater, but less to the desired purpose, heat). But I guess that fluorescent bulbs and lamps (mythically conceived by Filipinos to have been the creation of a Filipino surnamed Flores, although the Philippine government's Department of Science and Technologically has never yet succeeded in its efforts to verify such a lightening allegation) exude greater brightness of light with less disparity between copious heat and working light.

    Still, once the class of manufactured light is established, whether it be fluorescent or incandescent, and our lab does use incandescent bulbs as these, when fresh, are transparent enough, so that through their thin but egg-durable glass encasings we have a better than aquarium view of the filament and its very propping-stands inside--- does higher Wattage (power rating) mean stated for a bulb denote its relative brightness within its given class?

    Two of the three standard equation relations for electrical power in direct-current circuits have current figured in as a factor. P = IV is one. P = I2R, since V from the prior equation may be drawn out as IR, V = IR being another standard established relation.

    That either current or its square may be conceived as being directly proprtional to electrical power dissipated does not
    Let us spin within our reflection the triumvirate of power expressions again. Two of the these figure in current as a factor (once as itself; the other instance of expression has it embedded squared). Very much likewise, two of the these figure in voltage (potential difference) as a factor (once as itself; the other instance of expression has it embedded squared). Hence, expressibility of I = expressibility of V.

    Somewhat likewise, two of the these figure in voltage (potential difference) as a factor (once as itself; the other instance of expression has it embedded squared). However, the latter pointm establishes that expressibility of R < expressibility of I = expressibility of V.

    7. The bulbs would dim.

    8. The peculiarities of the attached circuit do matter. That is why an appliance such as a Hoover vacuum cleaner may indicate squarely on its packaging box that it draws a certain quantity of current (such as less than ten amperes), because the attach circuit via its resistance as load (Rload) determines how the voltage source will supply current.
    9. D = E > C

    10. Apparently , this question #10 applies only to Circuit 3. Well, keeping that in mind, we may appreciate the long-estavblished fact

    13. I'd say that our battery is a constant voltage source, rather than a constant current source.

    A = B > F when switch 2 is open while switch 1 is closed, as the body text has indicated for mimicking Circuit 2.

    When both its switches are thrown shut however, Circuit 4 may well be regarded as Giancoli's Figure 26-9 given a quarter-rotation clockwise. Hence, for our question 14 I will just rephrase Ginacoli's response that A > B = F, because the current running down Circuit 4 is bifurcated at junction point a into equal parts, such that current through B equals current through F which add up to what was current through A. Kirchoff's junctionm

    18. 12.7 milliAmperes

    19. Circuit 5's voltmeter will read a shade less than 6.5 volts
    20. The power dissipated will amount to 0.0829 Watts.
    I2R is preferable a power calculation than IV within this context, because we want to emphasize the role as factor of a resistance, R1, that is.
    21. 13 milliAmperes will flow through CIrcuit 6's ammeter.
    22. I predict that the voltage drop (Vab) across R2 would amount to 2.6 Volts, using V = IR for my calculation.
    23. I predict that the voltage drop (Vbc) across R3 would amount to 3.9 Volts, again using V = IR for my calculation.
    24. Vbattery = Vbat = Vab + Vbc = Vac
    25. I predict that the current (I4) through resistance R4 would amount to .0216 amperes.
    26. I would predict that the current (I5) through resistance R5 would amount to .0127(451) Amperes.
    27. I would predict that the current (Itotal) through the battery would amount to .0344 Amperes.
    28. I5 + I5 = Itotal
    29. 189 Ohms
    XC units =

    6.2831853...·(ab) Farads

    as 1 Volt = 1 Joule per Coulomb

    6.28..·(ab) Coulomb2
    C = b # of (milli/micro/pico-)Farads
    4 Hz25 mW40 Hz3978.9 W
    about four
    kiloW4x10n Hz3.9789x104-n W 5 Hz31 mWW 6 Hz38 mW 7 Hz44 mW 8 Hz50 mW 9 Hz57 mW9x10n Hz5.7x10n-5 W

  3. Around 1550 Hertz would work well for the RC ciruci9te. Around 361.7 Hertz woumight be good for the LR circuite.m Allin all, a range spanning from 500 to 200 hertz freequency would give an ample allowance for resalsts we;dwatch out for./
  4. 758.74 Hertz
  5. One Hundred (100) W hms
  6. Forty (40 mA) milliamperes
    please click to get to source of formula pic

Lab Proper


When we refer to either a capacitor or an inductor as being a "short" for a certain orientation of frequency (as the kind of thing we get Urone's Figure 22.44(b), where the capacitor shorts out high frequencies from a left-hand "black-box" circuit to ground, so as to deprive them from getting to the right-hand circuit), we would like to think of the component as, in effect, causing a short circuit (as contrasted to an open circuit) dishing off to ground a certain quality of wave-frequqency being fed into a circuit in which it has been installed.

What a fuse is to current, a non-resistor reactance-component is to frequency, and yet inductors and capacitors are ministers of a taller order against frequency extremities when compared to the foot-soliders that are fuses, which are like bees that sting to kill audacious uprisings of current, only to themselves ending out used up.

Consulting Tipler (Chapter 31 Section 3 page 962 Volume 2, Physics, Freeman), we find that the capacitor is indeed a short for high frequencies. The inductor shorts out both direct current and low-frequency alternating currents. This summary goes well with calculations of reactance. A capacitor becomes an open (rather than short) circuit with low frequencies that bend the reactance calculation's denominator so low that the numerator's mere value of one can end up translating into great achievements of reactance--- making the capacitor a dead end to the alternating current.

  • Conclusion

    10 Hertz15,915
    like sixteen kiloohms
    W Ohms
    200 Hz795.77 W
    300 Hz530.52 W
    400 Hz397.89 W
    1000 HertzW Ohms
    10000 HertzW Ohms
    100000 HertzW Ohms
    10000000 HertzW Ohms
    100 HertzW Ohms
    500 HertzW Ohms
    1000 HertzW Ohms
    10000 HertzW Ohms
    100000 HertzW Ohms
    10000000 HertzW Ohms