CBSE Questions for Class 12 Medical Physics Electrostatic Potential And Capacitance Quiz 6 - MCQExams.com

A soap bubble of radius $$\sqrt 7$$cm is blown. Work done in this process is used to store energy in capacitor at potential of $$1$$V using transducer. Charge stored is ________. 
$$(T=30 dyne/cm)$$
  • $$5.28\mu C$$
  • $$10.56\mu C$$
  • $$21.12\mu C$$
  • $$21.12 mC$$
Two charges of equal magnitude 'q' are placed in air at a distance '$$2a$$' apart and third charge '$$-2q$$' is placed at midpoint. The potential energy of the system is ________. 
($$\epsilon_0=$$ permittivity of free space)
  • $$\displaystyle -\frac{q^2}{8\pi \epsilon_0a}$$
  • $$\displaystyle -\frac{3q^2}{8\pi \epsilon_0a}$$
  • $$\displaystyle -\frac{5q^2}{8\pi \epsilon_0a}$$
  • $$\displaystyle -\frac{7q^2}{8\pi \epsilon_0a}$$
Figure shows three spherical and equipotential surfaces $$A$$, $$B$$ and $$C$$ around a point charge $$q$$. The potential difference $${ V }_{ A }-{ V }_{ B }={ V }_{ B }-{ V }_{ C }$$. If $${ t }_{ 1 }$$ and $${ t }_{ 2 }$$ be the distances between them, then :
467139_4d05d6ae617d4762986e426c472cf140.png
  • $${ t }_{ 1 }={ t }_{ 2 }$$
  • $${ t }_{ 1 }>{ t }_{ 2 }$$
  • $${ t }_{ 1 }<{ t }_{ 2 }$$
  • $${ t }_{ 1 }\le { t }_{ 2 }$$
High frequency capacitor offers
  • more resistance
  • less resistance
  • zero resistance
  • None of these
When a dielectric slab is introduced between the two plates of condenser then its capacity ___________.
  • remains constant
  • increases
  • decreases
  • may increase or decrease depending on the material of dielectric slab
A parallel plate condenser with oil (dielectric constant $$2$$) between the plates has capacitance $$C$$. If the oil is removed, the capacitance of capacitor becomes :
  • $$\sqrt {2C}$$
  • $$2C$$
  • $$\cfrac{C}{\sqrt {2}}$$
  • $$\cfrac{C}{2}$$
If dielectric is inserted in charged capacitor (battery removed ), then quantity that remains constant is.
  • Capacitance
  • Potential
  • Intensity
  • Charge
The capacity of parallel plate capacitor increases with the 
  • Increase of its distance
  • Increases of its area
  • Decreases of its area
  • None of the above
A parallel plate capacitor with a dielectric slab of dielectric constant $$3$$, filling the space between the plates, is charged to a potential $$ V$$. The battery is then disconnected and the dielectric slab is withdrawn. It is then replaced by another dielectric slab of dielectric constant $$2$$. If the energies stored in the capacitor before and after the dielectric slab is changed are $$\displaystyle { E }_{ 1 }$$ and $$\displaystyle { E }_{ 2 }$$, then $$\displaystyle { E }_{ 1 }/{ E }_{ 2 }$$ is:
  • $$\displaystyle \frac { 4 }{ 9 } $$
  • $$\displaystyle \frac { 2 }{ 3 } $$
  • $$\displaystyle \frac { 3 }{ 2 } $$
  • $$\displaystyle \frac { 9 }{ 5 } $$
An air filled parallel plate condenser has a capacity of $$2pF$$. The separation of the plates is doubled and the inter-space between the plates is filled with wax. If the capacity is increased to $$6$$pF, the dielectric constant of wax is.
  • $$2$$
  • $$3$$
  • $$4$$
  • $$6$$
Three particles, each having a charge of 10 $$\mu$$C are placed at the corners of an equilateral triangle of side 10 cm. The electrostatic potential energy of the system is :$$\displaystyle \left(\text{Given} \frac{1}{4\pi \in_0}=9\times 10^9N-m^2C^2\right)$$ 
  • Zero
  • $$\infty$$
  • 27 J
  • 100 J
In a capacitive circuit, dielectrics materials are placed between the plates of capacitors to
  • Speed the current flow
  • Slow the current flow
  • Reduce change leakage from the capacitor
  • increase change leakage from the capacitor
  • Increase capacitance of the capacitor
  • Decrease capacitance of the capacitor
Two positively charged particles are placed at different positions in a cube. In which diagram is the electrical potential energy of the pair of charges the greatest?
A student wants to increase the capacitance of a parallel-plate capacitor. How can he/she do this ?
  • Using smaller plates
  • Replacing the dielectric material between the plates with one that has a smaller dielectric constant
  • Decreasing the voltage between the plates
  • Increasing the voltage between the plates
  • Moving the plates closer together
In above shown figure, the two plates of the capacitor of charge +Q and -Q, which points lie on the same equipotential?
480542_43c73a9fbf034d4b9952093eed9dd2d6.png
  • 1 and 2 only
  • 1 and 3 only
  • 2 and 4 only
  • 3 and 4 only
  • 1, 2, 3, and 4 all lie on the same equipotential, since the electric field is uniform
The potential difference between the plate of a capacitor is increased by $$20$$%. The energy stored on the capacitor increases by:
  • $$20$$%
  • $$22$$%
  • $$40$$%
  • $$44$$%
If the charge on a capacitor is increased by $$2$$ coulomb, the energy stored in it increases by 21%. The original charge on the capacitor is :
  • $$10C$$
  • $$20C$$
  • $$30C$$
  • $$40C$$
Equipotential lines are shown, what is the approximate voltage at point P in the diagram?
494768_6cdbd7def77643efa1ca0518b1f4dfc3.png
  • 12 v
  • 8.0 v
  • 8.5 v
  • 6.0 v
Two parallel-plate of capacitor have charges +Q and -Q and potential difference $$\triangle V$$ due to charging, Now the capacitor is disconnected then the potential difference and the stored electrical potential energy is:
  • The potential difference decreases, and the stored electrical potential energy decreases
  • The potential difference decreases, and the stored electrical potential energy increases
  • The potential difference increases, and the stored electrical potential energy decreases
  • The potential difference increases, and the stored electrical potential energy increases
  • The potential difference decreases, and the stored electrical potential energy remains unchanged.
A dielectric is inserted into a capacitor while keeping the charge constant. Identify what happens to the potential difference and the stored energy?
  • The potential difference decreases and the stored energy increases
  • Both the potential difference and the stored energy increases
  • The potential difference increases and the stored energy decreases
  • Both the potential difference and the stored energy decrease
  • Both the potential difference and the stored energy remain the same
How much power is used in moving a $$0.03C$$ charge from point A at a potential of $$40V$$ to point B at $$60V$$, if this takes 2 seconds?
  • $$0.30W$$
  • $$0.15W$$
  • $$0.6W$$
  • $$0.012W$$
The diagram shows equipotential lines from an unknown charge configuration. Determine the direction of the field at A :
494766_0dc259c70087444188794baa518158b8.png
  • Up
  • Down
  • Left
  • Right
The diagram shows equipotential lines from an unknown charge configuration. Determine where in the diagram the field is closest to uniform :
494764_127e4ff8908e4d578c336c48314144d6.png
  • A
  • B
  • C
  • D
What is the change in potential energy of a particle of charge +q that is brought from a distance of 3r to a distance of 2r by a particle of charge q? 
  • $$kq^2/r$$
  • $$-kq^2/6r$$
  • $$kq^2/r^2$$
  • $$-kq^2//4r^2$$
  • $$8kq^2/r^2$$
A dielectric is inserted into a capacitor while the charge on it is kept constant. What happens to the potential difference and the stored energy? 
  • The potential difference decreases and the stored energy increases
  • Both the potential difference and the stored energy increase
  • The potential difference increases and the stored energy decreases
  • Both the potential difference and the stored energy decrease
  • Both the potential difference and the stored energy remain the same
Calculate the change in potential energy of a particle of charge $$+q$$ that is brought from a distance of $$3r$$ to a distance of $$2r$$ in the electric field of charge $$-q$$?
  • $${ k{ q }^{ 2 } }/{ r }$$
  • $${ -k{ q }^{ 2 } }/{ 6r }$$
  • $${ k{ q }^{ 2 } }/{ 4{ r }^{ 2 } }$$
  • $${ -k{ q }^{ 2 } }/{ 4{ r }^{ 2 } }$$
  • $${ k{ q }^{ 2 } }/{ { r }^{ 2 } }$$
A negative charge is located in the uniform electric field between two plates (not shown).
Where in the diagram will the electron have the greatest change in potential energy before hitting the one of the plates?
495993.png
  • A
  • B
  • C
  • D
The diagram shows three identical metal plates A, B, and C that are set parallel to each other. Plate A is farther from B than C is from B. A source of constant EMF is connected to the system such that B is connected to the positive terminal and A and C are connected to the negative terminal.
Which of the following diagrams correctly depicts the isolines of electric potential (shown as dotted lines) in the region between the plates?
496134.gif
A capacitor loses half of its voltage every 1 seconds.
If the initial Energy it holds is $$E$$, how much energy will it have after 3 seconds?
  • $$E/3$$
  • $$E/8$$
  • $$E/9$$
  • $$E/64$$
An air-filled capacitor has a capacitance of $$C^o$$. Then a dielectric with a dielectric constant of 3.0 is inserted into it and the plates are pushed toward each other so that the distance between the plates is reduced to $$\frac{1}{2}$$ the original value.
What is the new capacitance?
  • $$\frac{1}{6}C^o$$
  • $$\frac{2}{3}C^o$$
  • $$\frac{3}{2}C^o$$
  • $$6C^o$$
Three capacitors, $$3\mu F, 6\mu F$$ and $$6\mu F$$ are connected in series to a source of 120V. The potential difference, in volts, across the $$3\mu F$$ capacitor will be
  • 24
  • 30
  • 40
  • 60
 In context of a capacitor , which of the following statement is correct?
  • Electric field may be uniform
  • There must be some equipotential surface somewhere inside
  • Electric potential must be max at surface of one of the plate in case of parallel plate capacitor
  • None of the above
An electric dipole is kept in the origin with charges along the x axis, now choose the correct option,
  • equipotential surface is on $$xy$$ plane
  • equipotential surface is on $$xz$$ plane
  • equipotential surface is on $$yz$$ plane
  • none of the above
A capacitor contains two square plates with side lengths $$5.0$$ cm. The plates are separated by $$2.0$$ mm. Dry air fills the space between the plates. Dry air has a dielectric constant of $$1.00$$ and experiences dielectric breakdown when the electric field exceeds $$3.010^4 V/cm$$.
What is the magnitude of charge that can be stored on each plate before the capacitor exceeds its breakdown limit and sends a spark between the plates?
  • $$6.6\times 10^{-8}C$$
  • $$6.6\times 10^{-5}C$$
  • $$3.3\times 10^{-7}C$$
  • $$3.3\times 10^{-8}C$$
  • $$8.1\times 10^{-2}C$$
Electric potential is the force experienced by a unit positive charge placed at a point
  • True
  • False
The two capacitors $$2\mu F$$ and $$6\mu F$$ are put in series, the effective capacity of the system is $$\mu F$$ is:
  • $$8\mu F$$
  • $$2\mu F$$
  • $$3/2\mu F$$
  • $$2/3\mu F$$
When two capacitors of capacities of $$3\mu F$$ and $$6\mu F$$ are connected in series and connected to $$120\ V$$, the potential difference across $$3\mu F$$ is:
  • $$40\ V$$
  • $$60\ V$$
  • $$80\ V$$
  • $$180\ V$$
The equivalent capacitance of capacitors $$6\mu F$$ and $$3\mu F$$ connected in series is ______.
  • $$3\mu f$$
  • $$2\mu f$$
  • $$4\mu f$$
  • $$6\mu f$$
The amount of work done in moving a unit positive charge from infinity to a given point is known as:
  • Nuclear potential
  • Potential energy
  • Electric potential
  • Gravitational potential
An electric dipole is placed at the centre of a sphere, choose the correct options :
  • electric field is zero at every point on the surface
  • flux is zero across the surface
  • no circle is present in the sphere which is equipotential
  • none of the above
Which of the following pairs are analogous?
  • Energy and power
  • Gravitational potential energy and electric potential energy
  • Electric field and gravitational field
  • None of the above
A parallel plate capacitor is charged and then isolated. The effect of increasing the plate separation on charge, potential and capacitance respectively are:
  • constant, decreases, decreases
  • increases, decreases, decreases
  • constant, decreases, increases
  • constant, increases, decreases
Half of the space between the plates of a parallel-plate capacitor is filled with a dielectric material of dielectric constant K. The remaining half contains air as shown in the figure. The capacitor is now given a charge Q. Then
573796_e6408f35c15540368468063f1d0fe819.png
  • An electric field in the dielectric-filled region is higher than that in the air-filled region
  • On the two halves of the bottom plate the charge densities are unequal
  • Charge on the half of the top plate above the air-filled part is $$\dfrac{Q}{K +}$$
  • Capacitance of the capacitor shown above is $$(1+K)\dfrac{C_0}{2}$$, where $$C_0$$ is the capacitance of the same capacitor with the dielectric removed
A pendulum ( positively charged and hinged at some length above the plate) is swinging above a parallel plate (infinitely large and having negative charge),now consider the following statements, (consider gravity)
  • angular momentum about the hinge point of the ball will be max at lowest point
  • electric potential energy will be max at highest point
  • gravitational potential energy will be lowest at highest point
  • none of the above
Which of the following is a vector quantity?
  • Electric potential
  • Electric feild
  • Magnetic potential
  • Magnetic feild
In Fig., if the potential at point B is taken as zero, then the potential at point A will be?

1750774_03eca63da307420b8a2b6fd40493dc3f.PNG
  • $$8$$V
  • $$16$$V
  • $$24$$V
  • None of the above
The SI unit of electric potential is
  • $$Vm^{-1}$$
  • $$C$$
  • $$NC^{-1}$$
  • $$V$$
Three charges $$-q,Q \ and \ -q$$ are placed at equal distances on a straight line. If the total potential energy of the system of three charges is zero, then the ratio $$Q:q$$ is :
  • $$1:2$$
  • $$2:1$$
  • $$1:1$$
  • $$1:4$$
An electron of mass $$M_e$$, initially at rest, moves through a certain distance in a uniform electric field in time $$t_1$$. A proton of mass $$M_p$$ also intially at rest, takes time $$t_2$$ to move through an equal distance in this uniform electric field. Neglecting the effect of gravity, the ratio $$t_2 / t_1$$ is nearly equal to :
  • $$1$$
  • $$\sqrt{\dfrac{M_p}{M_e}}$$
  • $$\sqrt{\dfrac{M_e}{M_p}}$$
  • $$1836$$
                    is equal to the work done by an external agent in carrying a unit of positive charge from the arbitrarily chosen reference point (usually infinity) to that point without any acceleration.
  • Electric potential energy
  • Electric field
  • Electric potential
  • Electric potential difference
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