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NEET PHYSICSMedium

A series combination of n₁ capacitors, each of value C₁, is charged by a source of potential difference 4V. When another parallel combination of n₂ capacitors, each of value C₂, is charged by a source of potential difference V, it has the same (total) energy stored in it as the first combination has. The value of C₂ in terms of C₁ is:

A

2C₁ / (n₁n₂)

B

16 (n₂/n₁) C₁

C

2 (n₂/n₁) C₁

D

16C₁ / (n₁n₂)

Step-by-Step Solution

  1. Series Combination (Case 1):
  • Number of capacitors = n1n_1, Capacitance = C1C_1, Potential = 4V4V.
  • Equivalent capacitance for series combination (CsC_s) is given by 1Cs=n1C1Cs=C1n1\frac{1}{C_s} = \frac{n_1}{C_1} \Rightarrow C_s = \frac{C_1}{n_1} [1, 2].
  • Total energy stored (U1U_1) = 12Cs(4V)2=12(C1n1)16V2=8C1V2n1\frac{1}{2} C_s (4V)^2 = \frac{1}{2} \left(\frac{C_1}{n_1}\right) 16V^2 = \frac{8 C_1 V^2}{n_1} [3, 4].
  1. Parallel Combination (Case 2):
  • Number of capacitors = n2n_2, Capacitance = C2C_2, Potential = VV.
  • Equivalent capacitance for parallel combination (CpC_p) is given by Cp=n2C2C_p = n_2 C_2 [1, 2].
  • Total energy stored (U2U_2) = 12CpV2=12(n2C2)V2\frac{1}{2} C_p V^2 = \frac{1}{2} (n_2 C_2) V^2 [3, 4].
  1. Equating Energies:
  • Given U1=U2U_1 = U_2.
  • 8C1V2n1=n2C2V22\frac{8 C_1 V^2}{n_1} = \frac{n_2 C_2 V^2}{2}
  • 16C1n1=n2C2\frac{16 C_1}{n_1} = n_2 C_2
  • C2=16C1n1n2C_2 = \frac{16 C_1}{n_1 n_2}
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