Algebra

Two lamps can be connected to a battery in a circuit in series or in parallel. You can calculate the total resistance RT (t is down from r) in a circuit if you know the resistance in each lamp. Resistance is measured in ohms. For a circuit connected in series, RT = R1 + R2. For a circuit connected in parallel, 1/RT = 1/R1 + 1/R2.

a. The lamps are connected in parallel. RT = 12 ohms. Find R2.

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  1. just plug it into the formula:

    1/12 = 1/R1 + 1/R2
    Unless you know R1, you can't figure R2. If the lamps are identical, then R1=R2=24

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  2. I'm sorry, R1 = 30 ohms.

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  3. How do I do 1/12 = 1/30 + 1/R?

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  4. 1/R = 1/12 - 1/30
    1/R = 1/20
    R = 20

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