Two capacitors of capacitance $10\mu\text{F}$ and $20 \mu\text{F}$ are connected in series with a 6 V battery. After the capacitors are fully charged, a slab of dielectric constant (K) is inserted between the plates of the two capacitors. How will the following be affected after the slab is introduced:
  1. The electric field energy stored in the capacitors.
  2. The charges on the two capacitors.
  3. The potential difference between the plates of the capacitors.
Justify your answer.
CBSE OUTSIDE DELHI - SET 2 BHUBNESHWAR 2015
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The capacitance of both the capacitors increases by a factor K.
  1. New Electric field energy values are: = $\frac{1}{2}\text{k}(\text{c}_{1}\text{v}^{2}_{1}) \text{ and}\frac{1}{2}\text{k}(\text{c}_{2}\text{v}^{2}_{1}).$
  2. New charges are: =$\frac{1}{2}\text{KC}_{1}\text{V}_{1}\text{ and }\frac{1}{2}\text{KC}_{2}\text{V}_{2}.$
  3. New P.D values are: $V_1$ and $V_2$
(The battery remains connected to the capacitors)
Alternate Answer
  1. New Electric field energy values are: $\frac{1}{2}\frac{\text{Q}^{2}}{\text{KC}_{1}} \text{and } \frac{1}{2}\frac{\text{Q}^{2}}{\text{KC}_{2}}.$
  2. New charges are: Q and Q as before.
  3. New P.D values are: $\frac{\text{Q}}{\text{KC}_{1}} \text{and }\frac{\text{Q}}{\text{KC}_{2}}.$
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