BCECE Engineering BCECE Engineering Solved Paper-2004

  • question_answer
    Two wires have resistances R and 2R. When both are joining in series and in parallel, then ratio of heats generated in these situations on applying the same voltage, is:

    A)  2 : 1                                      

    B)         1 : 2

    C)         2 : 9                                      

    D)         9 : 2

    Correct Answer: C

    Solution :

    In series combination, the net resistance           \[{{R}_{s}}=R+2R=3R\] Heat produced in \[{{R}_{s}},\]                 \[{{H}_{s}}=\frac{{{V}^{2}}}{{{R}_{s}}}=\frac{{{V}^{2}}}{3R}\]                       ?(i) In parallel combination, the net resistance \[{{R}_{p}}=\frac{R\times 2R}{R+2R}=\frac{2{{R}^{2}}}{3R}=\frac{2}{3}R\] Heat produced in\[{{R}_{p}}\] \[{{H}_{p}}=\frac{{{V}^{2}}}{{{R}_{p}}}=\frac{{{V}^{R}}}{2R/3}=\frac{3{{V}^{2}}}{2R}\]                    ?(ii) Dividing Eq. (i) by Eq. (ii), we obtain              \[\frac{{{H}_{s}}}{{{H}_{p}}}=\frac{{{V}^{2}}/3R}{3{{V}^{2}}/2R}=\frac{2}{9}\]


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