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Current in circuit (bulbs)

  1. Jan 1, 2017 #1
    elec.JPG


    2. Relevant equations
    Power = VI

    3. The attempt at a solution

    Since lamp M breaks, lamp L gets more of the current so its brightness increases and lamp N's brightness stays the same because the current at point 2 is the same if the other lamp breaks or not, so N's brightness should not be affected.

    So my answer is A but the correct answer is D?? What have I done wrong?
     
  2. jcsd
  3. Jan 1, 2017 #2

    ehild

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    Gold Member

    The current through N will also change, as the resultant resistance changes when lamp M breaks.
     
  4. Jan 1, 2017 #3
    I get it now.

    since the parallel combo is no more, resistance has increased across the circuit so less current for both, so N decreases but L increases since it has more current in resistance than in parallel. Thanks.
     
  5. Jan 1, 2017 #4

    ehild

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    It is correct, but can you derive what are the powers on the lamps in both cases, to prove your statement? The EMF of the battery is E and each lamp has resistance r.
     
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