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NEET
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Physics
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Capacitance

NEET · Physics · Capacitance

A parallel plate capacitor of capacitance 50 is subjected to a...

A parallel plate capacitor of capacitance 50 μF50 \text{ } \mu\text{F} is subjected to a time-varying voltage. The voltage across the capacitor increases uniformly from 00 to 10 V10 \text{ V} in the time interval t=0t = 0 to t=2 mst = 2 \text{ ms}, and then remains constant at 10 V10 \text{ V} for t>2 mst > 2 \text{ ms}. The displacement current between the plates during the interval t=0t = 0 to t=2 mst = 2 \text{ ms} is:

Options

  1. A250 mA250 \text{ mA}
  2. B500 μA500 \text{ } \mu\text{A}
  3. C0.5 μA0.5 \text{ } \mu\text{A}
  4. DZero

Correct answer

A. 250 mA250 \text{ mA}

Step-by-step solution

The displacement current IdI_d is equal to the conduction current IcI_c during the charging of a capacitor, which is given by:
Id=CdVdtI_d = C \dfrac{dV}{dt}

During the interval t=0t = 0 to t=2 mst = 2 \text{ ms}, the voltage increases uniformly. The rate of change of voltage dVdt\dfrac{dV}{dt} is the slope of the voltage-time graph:
dVdt=V2−V1t2−t1\dfrac{dV}{dt} = \dfrac{V_2 - V_1}{t_2 - t_1}
dVdt=10−02×10−3−0=102×10−3=5000 V s−1\dfrac{dV}{dt} = \dfrac{10 - 0}{2 \times 10^{-3} - 0} = \dfrac{10}{2 \times 10^{-3}} = 5000 \text{ V s}^{-1}

Now, calculate the displacement current:
Id=(50×10−6 F)×(5000 V s−1)I_d = (50 \times 10^{-6} \text{ F}) \times (5000 \text{ V s}^{-1})
Id=250000×10−6 A=250×10−3 AI_d = 250000 \times 10^{-6} \text{ A} = 250 \times 10^{-3} \text{ A}
Id=250 mAI_d = 250 \text{ mA}

Note: Using the voltage value directly instead of its rate of change leads to the incorrect 500 μA500 \text{ } \mu\text{A}, which represents the total charge stored, not the current.

Answer: 250 mA250 \text{ mA}
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