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    http://www.scribd.com/mobile/doc/50654250?width=768

    I'm stuck on question 4. The correct answer is B.
    P=IV
    V=IR

    So P=I2R

    If the new lamp has twice the resistance, it has to have twice the power. So WHY isn't the correct answer C? I need an explanation so I can understand why B is right and not C.

    Thank you
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    Voltage is constant at 230V.

    P=IV. P=VI
    V=IR therefore V/R=I so P=V^2/R
    Double R, half the power
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    (Original post by pratstercs)
    Voltage is constant at 230V.

    P=IV. P=VI
    V=IR therefore V/R=I so P=V^2/R
    Double R, half the power
    I guess it is better to substitute I=V/R into P=VI.

    Thanks a lot.
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    (Original post by krisshP)
    I guess it is better to substitute I=V/R into P=VI.

    Thanks a lot.
    It's not necessarily better, you just need to remember that the current will change as the resistance changes
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    (Original post by pratstercs)
    It's not necessarily better, you just need to remember that the current will change as the resistance changes
    Thanks
 
 
 
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