Combination of Capacitors - NEET Physics Questions
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Combination of Capacitors

Question 1: moderate

Total capacity of the system of capacitors shown in the following figure between the points A and B is:

1. 1 μF
2. 2 μF
3. 3 μF
4. 4 μF
View Answer

Combination of Capacitors simple questions

The Circled capacitors are in Series so , Their equivalent capacitance is 1 μF . Then it is in parallel with 1 μF capacitor. The circuit will keep on reducing.

Question 2: moderate

The resultant capcitance between A and B in the figure is :

1. 1 μF
2. 10 μF
3. 50 μF
4. 1.5
View Answer

Combination of Capacitors question

For Such Question start solving from the farthest point. The circuit will keep on reducing.

 

Question 3: moderate

Consider the figure, equivalent capacitance between A and B is

1. C
2. 4C/5
3. 5C/4
4. 2C/3
View Answer

Capacitors circled in the diagram are short circuited so, they can be removed from the circuit.Combination of Capacitors

 

Question 4: moderate

Minimum number of 8 μF and 250 V capacitors used to make a combination of 16 μF and 1000 V are:

1. 32
2. 16
3. 8
4. 4
View Answer

To solve this, we determine the combination of capacitors required to achieve the desired capacitance and voltage.


Given:

  • Individual capacitor:
    C=8μFC = 8 \, \mu\text{F}
     

    , Vmax=250VV_{\text{max}} = 250 \, \text{V} 

  • Desired combination:
    Creq=16μFC_{\text{req}} = 16 \, \mu\text{F}
     

    , Vreq=1000VV_{\text{req}} = 1000 \, \text{V} 


Step 1: Voltage requirement

To achieve

Vreq=1000VV_{\text{req}} = 1000 \, \text{V}

, multiple capacitors must be connected in series because the voltage across a series combination adds up. The number of capacitors required in series is:

 

n=VreqVmax=1000250=4n = \frac{V_{\text{req}}}{V_{\text{max}}} = \frac{1000}{250} = 4

 

Thus, 4 capacitors in series are required to handle 1000 V.


Step 2: Capacitance in series

The effective capacitance of

nn

capacitors in series is given by:

 

Cseries=Cn=84=2μFC_{\text{series}} = \frac{C}{n} = \frac{8}{4} = 2 \, \mu\text{F}

 

So, a series of 4 capacitors provides

Cseries=2μFC_{\text{series}} = 2 \, \mu\text{F}

.


Step 3: Capacitance requirement

To achieve

Creq=16μFC_{\text{req}} = 16 \, \mu\text{F}

, multiple such series groups must be connected in parallel because capacitance in parallel adds up. The number of such series groups required is:

 

m=CreqCseries=162=8m = \frac{C_{\text{req}}}{C_{\text{series}}} = \frac{16}{2} = 8

 

Thus, 8 series groups are required.


Step 4: Total capacitors

Each series group contains 4 capacitors, and there are 8 such groups. Therefore, the total number of capacitors is:

 

Total capacitors=nm=48=32\text{Total capacitors} = n \cdot m = 4 \cdot 8 = 32

 


Final Answer:

The minimum number of capacitors required is:

 

32\boxed{32}

 

Question 5: difficult

Three capacitors 2 μF, 3 μF and 5 μF can withstand voltages to 3V, 2V and 1V respectively. Their series combination can withstand a maximum voltage equal to

1. 5 Volts
2. (31/6) Volts
3. (26/5) Volts
4. None
View Answer

Let's verify and calculate the correct answer step-by-step:

Given Data:

  • Capacitances:
    C1=2μF,C2=3μF,C3=5μFC_1 = 2 \, \mu\text{F}, C_2 = 3 \, \mu\text{F}, C_3 = 5 \, \mu\text{F}
     
  • Maximum voltages:
    V1=3V,V2=2V,V3=1VV_1 = 3 \, \text{V}, V_2 = 2 \, \text{V}, V_3 = 1 \, \text{V}
     

Step 1: Maximum charge each capacitor can store:

 

Q1=C1V1=23=6μCQ_1 = C_1 \cdot V_1 = 2 \cdot 3 = 6 \, \mu\text{C}

 

Q2=C2V2=32=6μCQ_2 = C_2 \cdot V_2 = 3 \cdot 2 = 6 \, \mu\text{C}

 

Q3=C3V3=51=5μCQ_3 = C_3 \cdot V_3 = 5 \cdot 1 = 5 \, \mu\text{C}

 

The capacitor with the minimum charge capacity limits the system. Here,

Qmax=5μCQ_{\text{max}} = 5 \, \mu\text{C}

, dictated by

C3C_3

.


Step 2: Voltage distribution across each capacitor:

In series, charge

QQ

is the same on all capacitors, and the voltage across each capacitor is:

 

V1=QC1,V2=QC2,V3=QC3V_1 = \frac{Q}{C_1}, \quad V_2 = \frac{Q}{C_2}, \quad V_3 = \frac{Q}{C_3}

 

Total voltage across the series combination:

 

Vtotal=V1+V2+V3V_{\text{total}} = V_1 + V_2 + V_3

 

Substitute

Q=5μCQ = 5 \, \mu\text{C}

:

 

V1=52=2.5V,V2=531.67V,V3=55=1VV_1 = \frac{5}{2} = 2.5 \, \text{V}, \quad V_2 = \frac{5}{3} \approx 1.67 \, \text{V}, \quad V_3 = \frac{5}{5} = 1 \, \text{V}

 


Step 3: Total voltage:

 

Vtotal=V1+V2+V3=2.5+1.67+1=156+106+66=316V.V_{\text{total}} = V_1 + V_2 + V_3 = 2.5 + 1.67 + 1 = \frac{15}{6} + \frac{10}{6} + \frac{6}{6} = \frac{31}{6} \, \text{V}.

 


Final Answer:

The maximum voltage the series combination can withstand is:

 

316V5.17V.\boxed{\frac{31}{6} \, \text{V}} \approx 5.17 \, \text{V}.

 

Question 6: difficult

A combination of capacitors is set up as shown in the figure. The magnitude of the electric field, due to a point charge Q (having a charge equal to the sum of the charges on the 4μF and 9μF capacitors), at a point distant 30 m from it, would equal :

1. 480 N/C
2. 240 N/C
3. 360 N/C
4. 420 N/C
View Answer
Question 7: moderate

In the given figure, find the charge flowing through section AB when switch S is closed:

 

1. \[C_{0}E/12\]
2. \[C_{0}E/4\]
3. \[C_{0}E/3\]
4. none of these
View Answer

When Switch is open Ceq= C/4 Charge given by the Battery is CE/4.

When Switch is open Ceq= C/3 Charge given by the Battery is CE/3.

Extra Charge flowing through the circuit it = \( \frac{CE}{3}-\frac{CE}{4}= \frac{CE}{12}\)

 

Question 8: moderate

The equivalent capacitance between points M and N is:

1. \[\frac{10}{11}C_{0}\]
2. \[2C_{0}\]
3. \[C_{0}\]
4. none of these
View Answer

Combination of Capacitors

Circircled ones are in parallel

Question 9: easy

If each capacitor has C = I F, the capacitance across P and Q is:

 

1. 0.5 F
2. 1 F
3. 2 F
4. infinity
View Answer

First Branch has a capacitance of 1F , for second branch it is 1/2F , for third branch it is 1/4 F and so, on . As all these branches are in parallel

\[ C_{eq}=C_{1}+C_{2}+C_{3}+....\]

\[ C_{eq}= 1 + \frac{1}{2} + \frac{1}{4}+ \frac{1}{8}+....=\frac{1}{1-\frac{1}{2}}=2\mu F\]

Question 10: difficult

The equivalent capacitance between A and B is :

1. 5C/7
2. 7C/5
3. 7C/12
4. 12C/7
View Answer

To find the equivalent capacitance for this cubical capacitor network, where each edge of the cube has a capacitance

CC

, here’s the shortest solution:

Step-by-Step:

  1. Symmetry analysis:
    • By symmetry, all corners of the cube can be grouped into equivalent potential nodes.
    • The cube's symmetry allows reduction to a simpler circuit.
  2. Key nodes:
    • Node
      AA
       

      is connected to one corner of the cube.

    • Node
      BB
       

      is connected to the diagonally opposite corner.

  3. Effective connections:
    • Due to symmetry, three capacitors are effectively in parallel between
      AA
       

      and an intermediate point.

    • Similarly, three capacitors are effectively in parallel between
      BB
       

      and the same intermediate point.

    • Two capacitors remain directly between
      AA
       

      and BB 

      .

  4. Simplification:
    • The three parallel capacitors at each node result in:
      Cparallel=3CC_{\text{parallel}} = 3C
       
    • The equivalent circuit becomes two
      3C3C
       

      capacitors in series with a 2C2C 

      capacitor: Series combination:1Ceq=13C+13C+12C\text{Series combination:} \quad \frac{1}{C_{\text{eq}}} = \frac{1}{3C} + \frac{1}{3C} + \frac{1}{2C} 

  5. Calculation:
    • Combine series:
      1Ceq=23C+12C=46C+36C=76C\frac{1}{C_{\text{eq}}} = \frac{2}{3C} + \frac{1}{2C} = \frac{4}{6C} + \frac{3}{6C} = \frac{7}{6C}
       
    • Invert to find
      CeqC_{\text{eq}}
       

      : Ceq=6C7×2=12C7C_{\text{eq}} = \frac{6C}{7} \times 2 = \frac{12C}{7} 

Thus, the equivalent capacitance is:

 

Ceq=12C7C_{\text{eq}} = \frac{12C}{7}