Department of Pre-University Education, KarnatakaPUC Karnataka Science Class 12
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A 100 Pf Capacitor is Charged to a Potential Difference of 24 V. It is Connected to an Uncharged Capacitor of Capacitance 20 Pf. What Will Be the New Potential Difference Across the 100 Pf Capacitor? - Physics


A 100 pF capacitor is charged to a potential difference of 24 V. It is connected to an uncharged capacitor of capacitance 20 pF. What will be the new potential difference across the 100 pF capacitor?

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Given : 

`C_1 = 100   "pF"`

V = 24 V

Charge on the capacitor `q = C_1V = 24 xx 100  "pC"`

Capacitance of the uncharged capacitor, `C_2 = 20  "pF"`

When the charged capacitor is connected with the uncharged capacitor, the net charge on the system of the capacitors becomes 

`q_1 + q_2 = 24 xx 100  "qC"`             ....(i)

The potential difference across the plates of the capacitors will be the same.

`q_1/C_1 = q_2/C_2`

⇒ `q_1/100 = q_2/20`

⇒ `q_1 = 5q_2`                ....................(ii)

From eqs. (i) and (ii), we get

`q_1+q_1/5 = 24 xx 100  "pc"`

⇒ `6q_1 = 5 xx 24 xx 100  "pC"`

⇒ `q_1 = (5xx24xx100)/(6) "pC"`

Now ,

`V_1 = q_1/C_1`

⇒ `(5xx24xx100  "pC")/(6xx100  "pF")` = 20 V

  Is there an error in this question or solution?
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HC Verma Class 11, Class 12 Concepts of Physics Vol. 2
Chapter 9 Capacitors
Q 19 | Page 166
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