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    Why cant I just use V=IR for the output voltage in this circuit? Is it because it wants the output voltage, not the voltage through the resistor? Is it that simple?

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    Its a voltage divider network.
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    Same thing as on the other thread

    (Original post by Joinedup)
    Absolutely!

    you'll do I=V/(Rfixed+RLDR) each time (resistances are added because they're in series)

    then

    VLDR=I x RLDR

    then on to the next value of LDR resistance and calculate the current again.
    except the stages are combined into one formula
    so in this case

    I=Vin / (R1+(R2) [eq1]

    Vout=I R2 [eq2]

    substitute eq1 for the I in eq2

    Vout=(R2 Vin ) / (R1+(R2)

    which is the same as what's shown in the book

    Vout=Vin x R2/(R1+R2)


    and all the rules are obeyed...
    same current in both series resistors
    sum of voltages across each individual series resistor adds up to the input voltage
    voltage across each individual resistor equals the current through that resistor multiplied by it's resistance
 
 
 
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