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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

A capacitor of capacitance 5.00 is charged to 24.0 V , while a...

A capacitor of capacitance 5.00μF5.00 \mu\text{F} is charged to 24.0 V24.0 \text{ V}, while a second capacitor of capacitance 6.0μF6.0 \mu\text{F} is charged to 12.0 V12.0 \text{ V}. The positive plate of the first capacitor is subsequently connected to the negative plate of the second, and vice versa. Determine the loss of electrostatic energy during this process.

Options

  1. A0.885 mJ0.885 \text{ mJ}
  2. B1.77 mJ1.77 \text{ mJ}
  3. C3.54 mJ3.54 \text{ mJ}
  4. D0.196 mJ0.196 \text{ mJ}

Correct answer

B. 1.77 mJ1.77 \text{ mJ}

Step-by-step solution

When the positive plate of the first capacitor is connected to the negative plate of the second, the common potential VV is given by:

V=C1V1−C2V2C1+C2V = \dfrac{C_1 V_1 - C_2 V_2}{C_1 + C_2}

The loss of electrostatic energy during this process is given by the formula:

ΔU=12C1C2C1+C2(V1+V2)2\Delta U = \dfrac{1}{2} \dfrac{C_1 C_2}{C_1 + C_2} (V_1 + V_2)^2

Substituting the given values C1=5.00μFC_1 = 5.00 \mu\text{F}, C2=6.0μFC_2 = 6.0 \mu\text{F}, V1=24.0 VV_1 = 24.0 \text{ V}, and V2=12.0 VV_2 = 12.0 \text{ V}:

ΔU=12×5.00×6.05.00+6.0×(24.0+12.0)2μJ\Delta U = \dfrac{1}{2} \times \dfrac{5.00 \times 6.0}{5.00 + 6.0} \times (24.0 + 12.0)^2 \mu\text{J}

ΔU=12×30.011.0×(36.0)2μJ\Delta U = \dfrac{1}{2} \times \dfrac{30.0}{11.0} \times (36.0)^2 \mu\text{J}

ΔU=1511×1296μJ\Delta U = \dfrac{15}{11} \times 1296 \mu\text{J}

ΔU=1944011μJ≈1767.27μJ\Delta U = \dfrac{19440}{11} \mu\text{J} \approx 1767.27 \mu\text{J}

ΔU≈1.77 mJ\Delta U \approx 1.77 \text{ mJ}
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