Question

In the given circuit, a charge of `+80muC` is given to the upper plate of the `4muF` capacitor. Then in the steady state, the charge on the upper plate of the `3muF` capacitor is

A. `+32 mu C`
B. `+40 mu C`
C. `+48 mu C`
D. `+80 mu C`

Answer 1

Correct Answer - C
In fig, if `Q_(2), Q_(3)` are the changes on `C_(2), C_(3)` respectively, then for the isolated system marked with dotted boundary.

`Q_(2) + Q_(3) - 80 = 0`
`Q_(2) + Q_(3) = 80` …(i)
As `C_(2)` and `C_(3)` are in parallel, therefore, potential difference across `C_(2)` and ` C_(3)` is same, i.e.,
`(Q_(2))/(C_(2)) = (Q_(3))/(C_(3))`
or `(Q_(2))/(Q_(3)) = (C_(2))/(C_(3)) = (2)/(3)`
Put in (i), `(2)/(3) Q_(3) + Q_(3) = 80`
`Q_(3) = (80xx3)/(5) = 48 mu C`