JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Assertion and Reason

  • question_answer
    Assertion             :       If the distance between parallel plates of a capacitor is halved and dielectric constant is made three times, then the capacitor becomes 6 times.             Reason     :   Capacity of the capacitor does not depend upon the nature of the material. [AIIMS 1997]

    A)             If both assertion and reason are true and the reason is the correct explanation of the assertion.

    B)             If both assertion and reason are true but reason is not the correct explanation of the assertion.

    C)             If assertion is true but reason is false.

    D)             If the assertion and reason both are false.

    E)                 If assertion is false but reason is true.

    Correct Answer: B

    Solution :

                By the formula capacitance of a capacitor                    \[{{C}_{1}}={{\varepsilon }_{0}}\times \frac{KA}{d}\propto \frac{K}{d}\]                    Hence, \[\frac{{{C}_{1}}}{{{C}_{2}}}=\frac{{{K}_{1}}}{{{d}_{1}}}\times \frac{{{d}_{2}}}{{{K}_{2}}}=\frac{{{K}_{1}}}{{{K}_{2}}}\times \frac{d/2}{3K}=\frac{1}{6}\] or \[{{C}_{2}}=6{{C}_{1}}\]                    Again for capacity of a capacitor \[C=\frac{Q}{V}\]             Therefore, capacity of a capacitor does not depend upon the nature of the material of the capacitor.


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