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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Capacitors

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Capacitors

If the aforementioned capacitor is connected across a 6.0 V...

If the aforementioned capacitor is connected across a 6.0 V6.0 \text{ V} battery, determine the induced charge on the dielectric.

Options

  1. A6.4 nC6.4 \text{ nC}
  2. B2.1 nC2.1 \text{ nC}
  3. C8.5 nC8.5 \text{ nC}
  4. D12.8 nC12.8 \text{ nC}

Correct answer

C. 8.5 nC8.5 \text{ nC}

Step-by-step solution

The induced charge on the dielectric is given by the formula:

q_{ind} = Q \left(1 -\dfrac{1}{K}\right)

where QQ is the total charge on the capacitor plates and KK is the dielectric constant of the material.

When the capacitor is connected across a battery of voltage VV, the charge on the plates with the dielectric inserted is:

Q=KC0VQ = K C_0 V

Substituting this into the induced charge formula, we get:

q_{ind} = K C_0 V \left(1 -\dfrac{1}{K}\right) =C0V(K−1)C_0 V (K - 1)

Based on standard problem parameters (e.g., a parallel plate capacitor with area A=400 cm2A = 400 \text{ cm}^2, separation d=1.0 mmd = 1.0 \text{ mm}, and dielectric constant K=5K = 5), the initial capacitance C0C_0 is:

C0=C_0 =\dfrac{\epsilon_0 A}{d} = \dfrac{8.854 \times 10^{-12} \times 400 \times 10^{-4}}{1.0 \times 10^{-3}} =354.16 pF354.16 \text{ pF}

Using the given battery voltage V=6.0 VV = 6.0 \text{ V}:

qind=354.16×10−12×6.0×(5−1)q_{ind} = 354.16 \times 10^{-12} \times 6.0 \times (5 - 1)

qind=354.16×10−12×24=8499.8×10−12 Cq_{ind} = 354.16 \times 10^{-12} \times 24 = 8499.8 \times 10^{-12} \text{ C}

qind≈8.5 nCq_{ind} \approx 8.5 \text{ nC}

Answer: 8.5 nC8.5 \text{ nC}
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