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JEE Main
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Physics
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Capacitance

JEE Main · Physics · Capacitance

A parallel plate capacitor with air as a dielectric has capacitance...

A parallel plate capacitor with air as a dielectric has capacitance CC. A slab of dielectric constant K,K, having same thickness as the separation between the plates is introduced so as to fill one fourth of the capacitor as shown in the figure. The new capacitance will be

A parallel plate capacitor with air as a dielectric has capacitance C . A slab of dielectric constant K, having same

Options

  1. A\left(K + 3\right)\dfrac{C}{4}
  2. B\left(K + 2\right)\dfrac{C}{4}
  3. C\left(K + 1\right)\dfrac{C}{4}
  4. DKC4\dfrac{KC}{4}

Correct answer

A. \left(K + 3\right)\dfrac{C}{4}

Step-by-step solution

The two condensers with KK and with air are in parallel. With air, C1=ε0d(3A4)=3ε0A4d{C}_{1} = \dfrac{{ε}_{0}}{d}\left(\dfrac{3A}{4}\right) = \dfrac{3{ε}_{0}A}{4d}

With medium, C2=ε0Kd(A4)=ε0AK4d{C}_{2} = \dfrac{{ε}_{0}K}{d}\left(\dfrac{A}{4}\right) = \dfrac{{ε}_{0}AK}{4d}

∴C′=C1+C2∴ C^{′} = {C}_{1} + {C}_{2}

or C′=3ε0A4d+ε0AK4d=ε0Ad[34+K4]<br/><br/>orC^{′} = \dfrac{3{ε}_{0}A}{4d} + \dfrac{{ε}_{0}AK}{4d} = \dfrac{{ε}_{0}A}{d} \left[\dfrac{3}{4} + \dfrac{K}{4}\right] <br/><br/>or\begin{cases}C^{′} = \dfrac{C}{4}\left(K + 3\right) & \left[∵ C = \dfrac{A{ε}_{0}}{d}\right]\end{cases}$$
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