question_answer

A \[4\mu F\]condenser is connected in parallel to another condenser of\[8\mu F\]. Both the condensers are then connected in series with a \[12\mu F\] condenser and charged to \[20\ volts\]. The charge on the plate of \[4\mu F\]condenser is                                                               [MP PET 1989]

A)                    \[3.3\mu C\]

B)                                      \[40\mu C\]

C)                    \[80\mu C\]                  

D)            \[240\mu C\]

Correct Answer: B

Solution :

           Equivalent capacitance of the circuit \[{{C}_{eq}}=6\mu F\] Charge supplied from source Q = 6 ´ 20 =120 mC Hence charge on the plates of 4 mF capacitor \[=Q'=\frac{4}{(4+8)}\times 120=40\mu C\]