A parallel plate capacitor is made of two dielectric blocks in series. One of the blocks has thickness d 1 and dielectric constant K 1 and the other has thickness d 2 and dielectric constant K 2 , as shown in the figure. This arrangement can be thought of as a dielectric slab of thickness d = d 1 + d 2 and effective dielectric constant K. The K is:

$\frac{\mathrm{K}_{1} \mathrm{~K}_{2}\left(\mathrm{~d}_{1}+\mathrm{d}_{2}\right)}{\mathrm{K}_{1} \mathrm{~d}_{2}+\mathrm{K}_{2} \mathrm{~d}_{1}}$

$\frac{\mathrm{K}_{1} \mathrm{~d}_{1}+\mathrm{K}_{2} \mathrm{~d}_{2}}{\mathrm{~d}_{1}+\mathrm{d}_{1}}$

$\frac{\mathrm{K}_{1} \mathrm{~d}_{1}+\mathrm{K}_{2} \mathrm{~d}_{2}}{\mathrm{~K}_{1}+\mathrm{K}_{2}}$

$\frac{2 \mathrm{~K}_{1} \mathrm{~K}_{2}}{\mathrm{~K}_{1}+\mathrm{K}_{2}}$

Physics - Electrostatic Potential Capacitance - Quiz-13

A student charges a capacitor in such a manner that it stores energy of 1 J. Now he wants to increase the potential energy to 4 J. He should:

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quadruple the potential difference across the capacitor without changing the charge
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double the potential difference across the capacitor without changing the charge
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double both the potential difference and charge
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double the charge without changing the potential difference

An electron beam passes between two parallel plate electrodes as shown in the diagram. The bottom plate is kept at zero potential, while a slowly varying positive voltage is applied to the upper plate, as shown in the graph. After passing between the plates the beam hits a screen and makes spot. Ignoring gravity , the spot is:

An electron passes between two parallel plate of a capacitor as sh

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deflected up
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deflected down
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deflected up then down
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deflected down then up

A parallel plate capacitor is charged from a cell and then isolated from it. The separation between the plates is now increased.

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the force of attraction between the plates will increased
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the field in the region between the plates will not change
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the energy stored in the capacitor will decrease
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the potential difference between the plates will decrease

A parallel plate capacitor has a parallel sheet of copper inserted between and parallel to the two plates without touching the plates. The capacity of the capacitor after the introduction of the copper sheet is (Assume thickness of sheet is negligible) -

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minimum when the copper sheet touches one of the plates.
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maximum when the copper sheet touches one of the plates
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does not vary for any positions of the sheet between the plates.
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lesser than that before introducing the sheet.

A parallel plate capacitor is charged by connecting it to a battery. The battery is disconnected and the plates of the capacitor are pulled apart to make the separation between the plates twice. Again the capacitor is connected to the battery (with same polarity) then:

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Charge from the battery flows into the battery after reconnection.
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Charge from capacitor flows into the battery after reconnection.
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The potential difference between the plates decreases when the plates are pulled apart.
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After reconnection of battery, potential difference between the plates will immediately become half of the initial potential difference (just after disconnecting the battery)

A capacitor C is charged to a potential difference V and battery is disconnected. Now if the capacitor plates are brought close slowly by some distance:

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some + ve work is done by external agent
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energy of capacitor will decrease
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energy of capacitor will increase
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none of the above

The separation between the plates of a isolated charged parallel plate capacitor is increased. Which of the following quantities will not change?

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charge on the capacitor
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potential difference across the capacitor
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energy of the capacitor
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energy density between the plates.

An isolated metallic sphere of radius R has an electric charge. It is connected by means of a conducting wire to a distant uncharged metallic sphere of radius r (r<R). Which of the following statements is/are correct?

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Total energy of the system must increase
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Total energy of the system must decrease
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Final surface charge densities on two spheres may be equal to each other
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None of these

An uncharged capacitor having capacitance C is connected across a battery of emf $ε$ . Now the capacitor is disconnected and then reconnected across the same battery but with reversed polarity. Then :

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after reconnection, work done by the battery is 2C $ε$ ²
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after reconnection, thermal energy produced in the circuit will be equal to two-third of the total energy supplied by the battery
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after reconnection, no energy is supplied by the battery
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after reconnection, half of the energy supplied by the battery is converted into heat.

When a parallel plate capacitor is connected to a source of constant potential difference-

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all the charge drawn from source is not stored in the capacitor.
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all the energy drawn from the source is stored in the capacitor.
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the potential difference across the capacitor grows very rapidly initially and this rate decreases to zero eventually.
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the capacitance increases with the increase of the charge in the capacitor.

Which of the following statements is true?

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The capacitance of a capacitor is the magnitude of net charge present on the two plates divided by the potential difference between the plates.
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The equivalent capacitance of two capacitors in parallel is always the sum of the two capacitances
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A dielectric material inserted between the conductors of a capacitor decreases its capacitance.
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The electrostatic energy stored in a capacitor is always more than the energy lost as heat when it is connected across a battery.

If the voltage across the series combination of capacitor C and 2C is increased, which capacitor will undergo breakdown first?

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C
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2C
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Both at same moment
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None of these

If the voltage across the parallel combination of two capacitors of C and 2C is increased, which capacitor will undergo breakdown first?

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C
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2C
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Both at same moment
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None of these

The work done to move a charge along an equipotential from A to B:

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can not be defined as $- \int_{A}^{B} E . dl.$
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must be defined as $- \int_{A}^{B} E . dl.$
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is zero.
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can have a non-zero value.

In the circuit shown in the figure initially key K₁ is closed and key K₂ is open. Then K₁ is opened and K₂ is closed (order is important).
[Take Q₁ and Q₂ as charges on C₁ and C₂ and V₁ and V₂as voltage respectively.]

Then,
a. charge on C gets redistributed such that V₁ = V₂

b. charge on C gets redistributed such that Q₁' = Q₂'

c. charge on C gets redistributed such that C₁V₁ + C₂V₂ = C₁E

d. charge on C gets redistributed such that Q₁'+ Q₂' = Q

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(a, c)
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(a, d)
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(b, c)
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(c, d)

If a conductor has a potential V $\neq$ 0 and there are no charges anywhere else outside, then

(a) there must be charges on the surface or inside itself

(b) there cannot be any charge in the body of the conductor

(d) there must be charges inside the surface

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(a, c)
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(a, d)
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(a, b)
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(c, d)

A parallel plate capacitor is connected to a battery as shown in the figure. Consider two situations.

A. Key K is kept closed and plates of capacitors are moved apart using the insulating handle.
B. Key K is opened and plates of capacitors are moved apart using the insulating handle.
Choose the correct option(s):
a. In A, Q remains the same but C changes.
b. In B, V remains the same but C changes.
c. In A, V remains the same and hence Q changes.
d. In B, Q remains the same and hence V changes.

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(a, b)
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(a, d)
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(b, c)
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(c, d)

2. A positively charged particle is released from rest in a uniform electric field. The electric potential energy of the charge:

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() remains constant because the electric field is uniform.
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() increases because the charge moves along the electric field.
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() decreases because the charge moves along the electric field.
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() decreases because the charge moves opposite to the electric field.

3 Figure shows some equipotential lines distributed in space. A charged object is moved from point A to point B.

(i) Fig. (ii) Fig. Fig(iii)

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() The work done in Fig. (i) is the greatest
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() The work done in Fig. (ii) is least
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() The work done is the same in Fig. (i), Fig. (ii) and Fig. (iii)
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() The work done in Fig. (iii) is greater than Fig. (ii) but equal to that in Fig. (i)

4. The electrostatic potential on the surface of a charged conducting sphere is 100 V. Two statements are made in this regard.
S₁: At any point inside the sphere, electric intensity is zero.
S₂: At any point inside the sphere, the electrostatic potential is 100 V.
Which of the following is a correct statement?

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() S₁ is true but S₁ is false.
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() Both S₁ and S₂ are false.
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() S₁ is true, S₂ is also true and S₁ is the cause of S_2.
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() S₁ is true, S₂ is also true but the statements are independent.

Equipotential at a great distance from a collection of charges whose total sum is not zero are approximately:

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spheres
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planes
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paraboloids
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ellipsoids

A parallel plate capacitor is made of two dielectric blocks in series. One of the blocks has thickness d₁ and dielectric constant K₁ and the other has thickness d₂ and dielectric constant K₂, as shown in the figure. This arrangement can be thought of as a dielectric slab of thickness d = d₁ + d₂ and effective dielectric constant K. The K is:

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$\frac{\mathrm{K}_{1} \mathrm{~d}_{1}+\mathrm{K}_{2} \mathrm{~d}_{2}}{\mathrm{~d}_{1}+\mathrm{d}_{1}}$
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$\frac{\mathrm{K}_{1} \mathrm{~d}_{1}+\mathrm{K}_{2} \mathrm{~d}_{2}}{\mathrm{~K}_{1}+\mathrm{K}_{2}}$
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$\frac{\mathrm{K}_{1} \mathrm{~K}_{2}\left(\mathrm{~d}_{1}+\mathrm{d}_{2}\right)}{\mathrm{K}_{1} \mathrm{~d}_{2}+\mathrm{K}_{2} \mathrm{~d}_{1}}$
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$\frac{2 \mathrm{~K}_{1} \mathrm{~K}_{2}}{\mathrm{~K}_{1}+\mathrm{K}_{2}}$

Consider a uniform electric field in the Z-direction. The potential is constant:
a. in all space
b. for any x for a given z
c. for any y for a given z
d. on the x-y plane for a given z

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(a, b, c)
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(a, c, d)
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(b, c, d)
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(c, d)

Equipotential surfaces:
a. are closer in regions of large electric fields compared to regions of lower electric fields.
b. will be more crowded near the sharp edges of a conductor.
c. will be more crowded near regions of large charge densities.
d. will always be equally spaced.

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(a, b, c)
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(a, c, d)
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(b, c, d)
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(c, d)

The variation of electrostatic potential with radial distance r from the centre of a positively charged metallic thin shell of radius R is given by the graph:

A parallel plate capacitor having cross-sectional area A and separation d has air in between the plates. Now an insulating slab of the same area but thickness d/2 is inserted between the plates as shown in the figure having dielectric constant K(=4). The ratio of new capacitance to its original capacitance will be?

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2: 1
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8: 5
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6: 5
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4: 1

The potential at a point P due to a charge of 4 × 10^–7C located 9 cm away is:

$1 . 3 \times 10^{6} V 2 . 4 \times 10^{6} V 3 . 3 \times 10^{4} V 4 . 4 \times 10^{4} V$

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1
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2
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3
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4

The potential at point P is $4 \times 10^{4} V$ . The work done in bringing a charge of 2 × 10^–9C from infinity to the point P is:

$1 . 6 \times 10^{- 6} J 2 . 4 \times 10^{- 4} J 3 . 8 \times 10^{- 5} J 4 . 9 \times 10^{- 4} J$

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1
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2
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3
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4

Two charges 3 × 10^–8 C and –2 × 10^–8 C are located 15 cm apart. At what point on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero.

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9 cm away from 3 × 10^–8 C
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25 cm away from 3 × 10^–8 C
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45 cm away from 3 × 10^–8 C
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Both (1) and (3)

Figures (a) and (b) show the field lines of a positive and negative point charge respectively.

The signs of the potential difference $V_{P} - V_{Q} and V_{B} - V_{A} are respectively :$

$1 . +, - 2 . +, + 3 . -, + 4 . -, -$

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1
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2
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3
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4

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Practice Physics Quiz Questions and Answers

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Practice Physics Quiz Questions and Answers

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