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Electrostatic Potential and Capacitance — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsElectrostatic Potential and Capacitance1 Mark
Question
For two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, and R is also false.
Assertion (A): The dielectric constant for metals is infinity.
Reason (R): When a charged capacitor is filled completely with a metallic slab, its capacity becomes very large.
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Answer

  1. A is true, but R is false.
Explanation:

The capacitance of a capacitor filled partially with a dielectric of thickness t given by,

$\text{C}=\frac{\in_0\text{A}}{\text{d-t}[1-\frac{1}{\text{K}}]}$

For metals, $\text{K}=\infty,$ $\therefore\text{C}=\frac{\in_0\text{A}}{\text{d-t}}.$

Now if the capacitor is filled completely with a metallic slab, then t = d, $\therefore\text{C}=\infty$ i.e., when a charged capacitor filled fully with a metallic slab, then capacitor is short circuited i.e., it will no more work as a capacitor.

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