Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2007

  • question_answer
    Two sphere of radii 4 cm and 6 cm are given \[80\text{ }\mu C\] and \[40\text{ }\mu C\]charges and both are joined by wire, then charge will flow.

    A)  \[32\mu C\] from A to B              

    B)  \[24\text{ }\mu C\] from A to B

    C)  \[32\text{ }\mu C\] from B to A               

    D)  None of the above

    Correct Answer: A

    Solution :

    Given,  \[{{r}_{1}}=4cm,\] \[{{r}_{2}}=6cm\] \[{{q}_{1}}=80\mu C,\] \[{{q}_{2}}=40\mu C\] Capacitances of spheres,                 \[{{C}_{1}}=4\pi {{\varepsilon }_{0}}{{r}_{1}},\] \[{{C}_{2}}=4\pi {{\varepsilon }_{0}}{{r}_{2}}\] On connecting the spheres, charge is redistributed in the ratio of their capacitances. \[\therefore \]  \[\frac{{{q}_{1}}'}{{{q}_{2}}'}=\frac{{{C}_{1}}}{{{C}_{2}}}=\frac{4\pi {{\varepsilon }_{0}}{{r}_{1}}}{4\pi {{\varepsilon }_{0}}{{r}_{2}}}\] \[\therefore \]  \[\frac{{{q}_{1}}'}{{{q}_{2}}'}=\frac{4}{6}=\frac{2}{3}\] \[\therefore \]  \[{{q}_{1}}'=\frac{2\times (80+40)}{(2+3)}=\frac{2\times 120}{5}\]                 \[=48\mu C\] \[\therefore \] Charge flown from first sphere to second sphere                                 \[=80-48-32\mu C\]


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