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Electric Charges and Fields — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsElectric Charges and Fields1 Mark
MCQ
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.
Assertion $(A):$ If a conducting medium is placed between two charges, then electric force between them becomes zero.
Reason $(R):$ Reduction in a force due to introduced material is inversely proportional to its dielectric constant.
  • A
    Both $A$ and $R $ are true, and $R$ is the correct explanation of $A.$
  • B
    Both $A$ and $R$ are true, but $R$ is not the correct explanation of $A.$
  • C
    $A$ is true but $R$ is false.
  • ✓
    $A$ is false and $R$ is also false.
✓

Answer

Correct option: D.
$A$ is false and $R$ is also false.
The dielectric constant of any material is $\text{K}=\frac{\text{E}_0}{\text{E}}=\frac{\frac{\text{F}_0}{\text{q}}}{\frac{\text{F}}{\text{q}}}=\frac{\text{F}_0}{\text{F}}$
$\Rightarrow\text{F}=\frac{\text{F}_0}{\text{K}},$ where $F_0$ is force when conductor is not present between the charge. Fis a force after introduction of conductor between charges.
Since dielectric constant of a conducting medium is infinity therefore $F = 0.$

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