Physics

Determine the total resistance of each of the following parallel circuits.
A. A parallel circuit with a 20-ohm resistor and a 10-ohm resistor.
B. A parallel circuit with two 20-ohm resistors and a 10-ohm resistor.
C. A parallel circuit with a 15-ohm light bulb and a 20-ohm resistor.
D. A parallel circuit with two 100-ohm resistors and a 20-ohm resistor.
E. A parallel circuit with a 10-ohm, 20-ohm, 100-ohm and 200-ohm resistor.

I'm not sure how to calculate this and I can't find much about it. Please help me and thank you.

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  1. I just found this formula: 1/Rt = 1/R1 + 1/R2 + 1/R3 +...
    Rt = R (t)otal
    But I don't know how to use it can someone please help me?

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  2. parallel circuits, you have the formula. There is a better way, less algebra, convert to conductances.
    A. A parallel circuit with a .050 mho resistor and a .10mho resistor.
    B. A parallel circuit with two .050 moh resistors and a .1mho resistor.
    C. A parallel circuit with a 15-ohm light bulb and a 20-ohm resistor.
    D. A parallel circuit with two 100-ohm resistors and a 20-ohm resistor.
    E. A parallel circuit with a 10-ohm, 20-ohm, 100-ohm and 200-ohm resistor.
    so you see, I did the reciprocal in A, B to get mhos, 1mho=1/ohm; conductance = 1/resistance.

    Now, I will do B for you.
    Conductance total= Ct= C1+C1 + C3
    = .050+.050+.1=.2mho
    resistancetotal=1/Ct=1/.2= 5 ohms

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    bobpursley

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