AMU Medical AMU Solved Paper-2009

  • question_answer
    Consider a parallel plate capacitor with plates 20 cm by 20 cm and separated by 2 mm. The dielectric constant of the material between the plates is 5. The plates are connected to a voltage sources of 500 V. The energy density of the field between the plates will be close to

    A) \[\text{2}.\text{65J}{{\text{m}}^{\text{-3}}}\]                                  

    B)  \[\text{1}.\text{95J}{{\text{m}}^{\text{-3}}}\]

    C)  \[\text{1}.38\text{J}{{\text{m}}^{\text{-3}}}\]                                 

    D)  \[0.69\,\text{J}{{\text{m}}^{\text{-3}}}\]

    Correct Answer: C

    Solution :

                     Energy density \[=\frac{Energy}{Volume}=\frac{1}{2}{{\varepsilon }_{0}}{{E}^{2}}\]                                 \[=\frac{1}{2}{{\varepsilon }_{0}}{{\left[ \frac{V}{d} \right]}^{2}}\] Here, as the dielectric is inserted between the plates and plates are connected to a voltage source. Energy density \[=\frac{1}{2}{{\varepsilon }_{0}}K{{\left[ \frac{V}{d} \right]}^{2}}\] Given, \[K=5,\,\,V=500\]volt, \[d=2\times {{10}^{-3}}m\]                 \[u=\frac{1}{2}\times 8.85\times {{10}^{-12}}\times 5\times {{\left[ \frac{500}{2\times {{10}^{-3}}} \right]}^{2}}\]                 \[=1.38\,J{{m}^{-3}}\]


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