Capacitance(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

CAPACITANCE MCQs

Total Questions : 26 | Page 1 of 3 pages

Question 1. The capacity of each condenser in the following fig. is ‘C’. Then the equivalent capacitance across A and B is?

Discuss Question

Answer: Option C. -> 4C3
:
C

C_{A B} = 2 \frac{2 c}{3} = \frac{4 c}{3}

Question 2. A parallel plate air condenser has a capacity ‘C’. When the plate separation is halved and a dielectric of constant k is inserted, new capacitance is found to be 12C. The value of dielectric constant ‘k’ is?

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Answer: Option C. -> 6
:
C

C = \frac{ϵ_{0} A}{d}; C^{1} = \frac{k ϵ_{0} A}{(\frac{d}{2})}

\frac{C^{1}}{C} = 2 k;

12 = 2 k; k = \frac{12}{2} = 6

Question 3.
In an adjoining figure are shown three capacitors C₁,C₂ and C₃ joined to a
battery. The correct condition will be (Symbols have their usual meanings)

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Answer: Option C. -> 6
:
C
Q₁=Q₂+Q₃because in series combination charge is same on both the
condenser and V=V₁+V₂because in parallel combination V₂=V₃
HenceV=V₁+V₂

Question 4. In the circuit given below potential difference across 6

μ

F capacitor is

In The Circuit Given Below Potential Difference Across 6 μ ...

Discuss Question

Answer: Option B. -> 4 V
:
B

q = C_{1} V_{1} = C^{1} V_{2}

\frac{V_{1}}{V_{2}} = \frac{C^{1}}{C_{1}} = \frac{9}{4.5} = \frac{2}{1}

\frac{V_{1} + V_{2}}{V_{2}} = \frac{2 + 1}{1}

V_{2} = \frac{12}{3} = 4 V

Question 5. If in the infinite series circuit, C = 9

μ

F and

C_{1} = 6 μ F

then the capacity across AB is

If In The Infinite Series Circuit, C = 9 μF And C1=6μF th...

1.25μF
6μF
3μF
12μF

Discuss Question

Answer: Option C. -> 3μF
:
C

\frac{1}{C_{A B}} = \frac{1}{c} + \frac{1}{c_{1} + x} + \frac{1}{c}

\frac{1}{x} = \frac{1}{9} + \frac{1}{6 + x} + \frac{1}{9}

\frac{1}{x} - \frac{1}{6 + x} = \frac{2}{9}

\frac{6 + x - x}{x (6 + x)} = \frac{2}{9}

27 = x (6 + x)

x = 3 μ F

Question 6. A parallel plate condenser initially has air as a medium between the plates. If a slab of dielectric constant 5 having thickness half the distance of separation between the plates is introduced, the percentage increase in its capacity will be ___

33.3%
66.7%
50%
75%

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Answer: Option B. -> 66.7%
:
B

C_{1} = \frac{ϵ_{0} A}{d}; C_{2} = \frac{ϵ_{0} A}{d - t + \frac{t}{k}} = \frac{ϵ_{0} A}{\frac{d}{2} + \frac{d}{10}}

C_{2} = \frac{10}{6} \frac{ϵ_{0} A}{d} = \frac{5 ϵ_{0} A}{3 d}

\frac{C_{2}}{C_{1}} = \frac{5}{3}; (\frac{C_{2}}{C_{1}} - 1) 100 % = (\frac{5}{3} - 1) 100 %

= 2 \times 33.3 %

= 66.67 %

Question 7. A piece of cloud has area

25 \times 10^{6} m^{2}

and electric potential of

10^{5}

volts. If the height of cloud is 0.75 km , then energy of electric field between earth and cloud will be?

250 J
750 J
1225 J
1475 J

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Answer: Option D. -> 1475 J
:
D
Energy =

\frac{1}{2} ϵ_{0} E^{2} \times (A \times d) = \frac{1}{2} ϵ_{0} (\frac{V^{2}}{d^{2}}) A d

= \frac{1}{2} \times \frac{8.85 \times 10^{- 12} \times (10^{5})^{2} \times 25 \times 10^{6}}{0.75 \times 10^{3}} = 1475 J

Question 8. The capacitance of a parallel plate condenser is C. The plates are square plates of side 1 unit. The plates are replaced by circular plates of diameter 1 unit. The capacitance now becomes?(with all others parameters remaining the same)

4 πC
πC
πC4
4Cπ

Discuss Question

Answer: Option C. -> πC4
:
C

C = \frac{ϵ_{0} l^{2}}{d} - - - - - - (1)

C^{1} = \frac{ϵ_{0} π l^{2}}{4 d} - - - - - - (2)

\frac{C^{1}}{C} = \frac{π}{4}

C^{1} = \frac{π}{4} c

Question 9. A parallel plate condenser of capacity 5

μ

F is kept connected to a battery of emf 10 V. If the space between the plates is filled with a medium of dielectric constant 12, then the additional charge taken from the battery is?

400 μc
450 μc
500 μc
550 μc

Discuss Question

Answer: Option D. -> 550 μc
:
D

q_{1} = c_{1} V = 5 \times 10^{- 6} \times 10 = 50 μ c

q_{1}^{1} = k c_{1} v = 12 \times 5 \times 10^{- 6} \times 10 = 600 μ c

A d d . C h a r g e = q_{1}^{1} - q_{1} = 600 - 50

= 550 μ C

Question 10. A conducting sphere of radius R, and carrying a charge q is joined to a conducting sphere of radius 2R, and carrying a charge – 2q. The charge flown between them will be?

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Answer: Option D. -> 4q3
:
D
Initial charge on sphere of radius R = q
Charge on this sphere after joining