CBSE Questions for Class 12 Medical Physics Electric Charges And Fields Quiz 11 - MCQExams.com

An electric dipole is placed in a non-uniform electric field, then _______.
  • The resultant force acting on the dipole is always zero
  • Torque acting on it may be zero
  • The resultant force acting on the dipole may be zero
  • Torque acting on it is always zero
A constant potential difference is applied between two horizontal metal plates. A charged oil droplet is held stationary by the electric field between the plates.
As some of the oil evaporates, the droplet loses mass and starts to accelerate. Its charge remains constant.
In which direction does the droplet accelerate, and which change needs to be made to the separation of the plates in order to stop this acceleration?

direction of accelerationseparation of the plates
Adownwardsdecrease
Bdownwardsincrease
Cupwardsdecrease
Dupwardsincrease


1648453_419542e019f24a5f84cf96c445e0afec.png
  • A
  • B
  • C
  • D
Coulomb's law is applicable to
  • Point charges
  • Spherical charges
  • Like charges
  • All of these
Force between the protons and neutrons in a nucleus is
  • Only coulombian
  • Only nuclear
  • Both (a) and (b)
  • None of these
The electric field in space given by $$\overset{\rightarrow}{E}=E_0\sin(\Omega t+6y-8z)\hat{n}$$ then the direction of propagation of light wave is
  • $$\dfrac{-3\hat{j}-4\hat{k}}{5}$$
  • $$\dfrac{-3\hat{j}+4\hat{k}}{5}$$
  • $$\dfrac{-3\hat{j}-8\hat{k}}{5}$$
  • $$\dfrac{3\hat{j}-4\hat{k}}{9}$$
If the potential at each point on a conductor is same to each other, then
  • Electric lines of force may begin or end on the same conductor
  • No electric lines of force may begin or end on the same conductor
  • The electric field inside the conductor may be non-zero
  • None of the above
Three charges of $$q_{1} = 1\times 10^{-6}C, q_{2} = 2\times 10^{-6}C$$ and $$q_{3} = -3\times 10^{-6}C$$ have been placed as shown. Then, the net electric flux will be maximum for the surface.
1751230_efe74cfa5a7644b0b22cca9fc4c68ca7.jpg
  • $$S_{1}$$
  • $$S_{2}$$
  • $$S_{3}$$
  • Same for all three
If a conductor is electrically neutral, then
  • net charge on it should be zero
  • potential on it should be zero
  • both charge and potential should be zero
  • none of them may not be zero
Number of electric lines of force from $$0.5\ C$$ of positive charge in a dielectric medium of dielectric constant $$10$$ is
  • $$5.65\times 10^{9}$$
  • $$1.13\times 10^{11}$$
  • $$9\times 10^{9}$$
  • $$8.85\times 10^{-12}$$
The surface that have zero flux are
  • $$S_{2}, S_{4}$$ and $$S_{2}$$
  • $$S_{1}, S_{3}, S_{4}$$ and $$S_{6}$$
  • $$S_{1}, S_{2}$$ and $$S_{3}$$
  • $$S_{2}, S_{3}$$ and $$S_{4}$$
If a body is charged by rubbing it, its weight
  • always decreases slightly
  • always increases slightly
  • may increase slightly or may decrease slightly
  • remains precisely the same
An electron is released from rest in a region of space with a non-zero electric field. Which of the following statements is true?
  • The electron will begin moving towards a region of higher potential.
  • The The electron will begin moving towards a region of lower potential.
  • The The electron will begin moving among a line of constant potential.
  • Nothing can be concluded unless the direction of the electric field is known.
Mark the correct statement:
  • If E is zero at certain point, then V should be zero at that point.
  • If E is not zero at certain point, then V should not be zero at that point.
  • If V is zero at certain point, then E should be zero at that point.
  • If V is zero at certain point, then E may or may not be zero.
The number of electrons and protons in an atom are same.
  • True
  • False
If a glass rod rubbed with silk is brought near the cap of a negatively charged electroscope, the divergence of leaves will decrease.
  • True
  • False
To find whether a body is charged or not, an uncharged electroscope is used.
  • True
  • False
To find whether the charge on a body is positive or negative, an uncharged electroscope is used.
  • True
  • False
An electron and a proton are at a distance of $$1$$ A. The dipole moment of the system is :
  • $$3.2 \times 10^{-29}\,Cm$$
  • $$1.6 \times 10^{-19}\,Cm$$
  • $$1.6 \times 10^{-29}\,Cm$$
  • $$3.2 \times 10^{-19}\,Cm$$
4 charges are placed each at a distance 'a' from an origin. The dipole moment of
configuration is:

41406_6904cffbfa944d8a8f923333a5fdaefd.png
  • $$2qa\hat{j}$$
  • $$3qa\hat{j}$$
  • $$2qa[\hat{i}+\hat{j}]$$
  • none
A hemispherical body is placed in a uniform electric field E. What is the flux linked with curved surface, if field is perpendicular to base in figure.
112103.jpg
  • $$2\pi R^2E$$
  • $$\pi R^2E/2$$
  • $$\pi R^2E$$
  • Zero
Consider a uniform electric field $$E=3\times 10^3 \hat i \: N/C$$. What is the flux of this field through a square of $$10\  cm$$ on a side whose plane is parallel to the yz plane?
  • $$30 \:N m^2/C$$
  • $$40 \:N m^2/C$$
  • $$50 \:N m^2/C$$
  • $$60 \:N m^2/C$$
In the figure, there are four arcs carrying positive and negative charges. All of them have same charge density $$\lambda$$. Pick incorrect statement(s).
75971.png
  • The net dipole moment for the given charge distribution is $$(4\sqrt{5})\lambda R^2$$.
  • The resultant electric field at the center is zero.
  • If a uniform $$\overrightarrow{E}$$ is switched on perpendicular to the plane, charge distribution starts rotating about X-axis.
  • Potential at the centre of the given charge distribution is non-zero.
Two infinite sheets of uniform charge density $$+\sigma $$ and $$-\sigma $$ are parallel to each other as shown in the
figure. Electric field at the




41413_1e518ce02201476ba10a9146c5f1e452.png
  • points to the left or to the right of the sheets is zero.
  • midpoint between the sheets is zero
  • midpoint of the sheets is $$\sigma /\varepsilon _{0}$$ and is directed towards right.
  • midpoint of the sheet is $$2\sigma /\varepsilon _{0}$$ and is directed towards right.
Electric flux through a surface of area $$100\ m^{2}$$ lying in the xy plane is (in V-m) if $$\vec{E}=\hat{i}+\sqrt{2}\hat{j}+\sqrt{3\hat{k}}$$
  • $$100$$
  • $$141.4$$
  • $$173.2$$
  • $$200$$
In the figure there are four arcs carrying positive and negative charges. All of them have same charge density $$\lambda$$. Pick incorrect statement(s) :

76169_af8603387ae140e2a6cc992f5183ca61.png
  • The net dipole moment for the given charge distribution is $$(4\sqrt 5)\lambda R^2$$.
  • The resultant electric filed at thee center is zero.
  • If a uniform $$\vec E$$ is switched on perpendicular to the plane then charge distribution starts rotating about X-axis.
  • Potential at the centre of the given charge distribution is non-zero.
A point charge $$q$$ is revolving in a circle of radius $$' r '$$ around a fixed infinite line charge with positive charge $$\lambda$$ per unit length. Now the point charge is shifted and it revolves in a circle of radius $$ 2 r $$. Then :
  • speed of the point charge $$q$$ remain constant
  • speed of the point charge $$q$$ will be change
  • angular velocity of the point charge $$q$$ about line charge does not change
  • work done by all forces is non-zero
Let $$E_1(r), E_2(r)$$ and $$E_3(r)$$ be the respective electric fields at a distance r from a point charge Q, an infinitely long wire with constant linear charge density $$\lambda$$, and an infinite plane with uniform surface charge density $$ \sigma $$. lf $$E_1(r_0) = E_2(r_0) = E_3(r_0)$$ at a given distance $$r_0$$, then :
  • $$Q = 4\sigma\pi {r_0}^{2}$$
  • $$r_0 = \dfrac{\lambda}{2 \pi\sigma}$$
  • $$E_1(\dfrac{r_0}{2}) = 2E_2(\dfrac{r_0}{2})$$
  • $$E_2(\dfrac{r_0}{2}) = 4E_3(\dfrac{r_0}{2})$$
A dipole is placed in a shell as shown. Find the electric flux emerging out of the shell and in a hypothetical sphere of radius r as shown.
142826_a32b9a3dc0b34db8b8415ec5ed2ad0ab.png
  • $$\displaystyle \frac{2q}{\varepsilon_{0}},0$$
  • $$\displaystyle \frac{q}{\varepsilon_{0}},\, \frac{-q}{\varepsilon_{0}}$$
  • $$\displaystyle \frac{-q}{\varepsilon_{0}},\, \frac{q}{\varepsilon_{0}}$$
  • $$0, \, 0$$
The charge per unit length for a very long straight wire is $$\lambda$$. The electric field at points near the wire (but outside it) and far from the ends varies with distance r as :
  • r
  • 1/r
  • 1/r$$^2$$
  • 1/r$$^3$$
Three point charges of 2q, -q and -q are placed at the corner of an equilateral triangle of side a. Then:
  • the potential at the centroid of the triangle is zero
  • the electric field at the centroid of triangle is zero
  • the dipole moment of the system is $$\sqrt { 2 } qa\ \hat j$$
  • the dipole moment of the system is $$\sqrt { 3 } qa\ \hat j$$
A small electric dipole having dipole moment $$\vec {p} $$ is placed along X-axis, as shown in the figure. A semi-infinite uniformly charged di-electric thin rod  placed along x axis, with one end coinciding with origin. If linear charge density of rod is $$+\lambda$$ and distance of dipole from rod is 'a', then calculate the electric force acting on dipole.
120551_7bcdfa99abc14188ba46ca0993ca285d.png
  • $$\displaystyle \frac{- P\lambda}{2\pi \epsilon_0 a^2}$$
  • $$\displaystyle \frac{- 3P\lambda}{4\pi \epsilon_0 a^2}$$
  • $$\displaystyle \frac{- 3P\lambda}{2\pi \epsilon_0 a^2}$$
  • $$\displaystyle \frac{- P\lambda}{4\pi \epsilon_0 a^2}$$
Electric charges q, q, -2q are placed at the corners of an equilateral triangle ABC of side $$l$$. The magnitude of electric dipole moment of the system is:
  • $$ql$$
  • $$2ql$$
  • $$\sqrt{3} ql$$
  • $$\displaystyle \frac{\sqrt{3}}{2} ql$$
A charged ball B hangs from a silk thread S which makes an angle $$\theta$$ with a large charged conducting sheet P as shown in the given figure. The surface charge density $$\sigma$$ of the sheet is proportional to :
142292_df61aebc6d2f49a784ffa3a54302b054.png
  • $$cos \, \theta$$
  • $$cot \, \theta$$
  • $$sin \, \theta$$
  • $$tan \, \theta$$
Find the force experienced by a semicircular rod having a charge q as shown in figure. Radius of the wire is R, and the line of charge with linear charge density $$\lambda$$ passes through its center and is perpendicular to the plane of wire.
154860_41292e687884435d9291986e690f012c.png
  • $$\displaystyle \frac{\lambda q}{2 \pi^2 \varepsilon_0 R}$$
  • $$\displaystyle \frac{\lambda q}{\pi^2 \varepsilon_0 R}$$
  • $$\displaystyle \frac{\lambda q}{4 \pi^2 \varepsilon_0 R}$$
  • $$\displaystyle \frac{\lambda q}{8 \pi^2 \varepsilon_0 R}$$
One-fourth of a sphere of radius R is removed as shown in Fig. An electric field E exists parallel to the xy plane. Find the flux through the remaining curved part :
159071_cf11a4a833ae439f9f0aad84004182fa.png
  • $$\pi R^2E$$
  • $$\sqrt2 \pi R^2E$$
  • $$\pi R^2E/ \sqrt2$$
  • none of these
A long cylindrical wire carries a linear charge density of $$3\times 10^{-8} Cm^{-1}$$. An electron revolve around it in a circular path under the influence of the attractive force. $$KE$$ of the electron is :
  • $$1.44 \times 10^{-7} J$$
  • $$2.88 \times 10^{-17} J$$
  • $$4.32 \times 10^{-17} J$$
  • $$8.64 \times 10^{-17} J$$
The electric field on two sides of a large charged plate is shown in Fig. The charge density on the plate in SI units is given by ($$\varepsilon_{0} $$ is the permittivity of free space in SI units) :
159058.png
  • $$2\varepsilon_{0}$$
  • $$4\varepsilon_{0}$$
  • $$10\varepsilon_{0}$$
  • Zero
A system consists of a thin charged wire ring of radius r and a very long uniformly charged wire oriented along the axis of the ring, with one of its ends coinciding with the center of the ring. The total charge on the ring is q, and the linear charge density on the straight wire is $$\lambda$$. The interaction force between the ring and the wire is :
  • $$\displaystyle \frac{\lambda q}{4 \pi \varepsilon_0 r}$$
  • $$\displaystyle \frac{\lambda q}{2 \sqrt{2} \pi \varepsilon_0 r}$$
  • $$\displaystyle \frac{2 \sqrt{2} \lambda q}{\pi \varepsilon_0 r}$$
  • $$\displaystyle \frac{4 \lambda q}{\pi \varepsilon_0 r}$$
A charged particle $$q$$ is placed at the centre $$O$$ of cube of side $$L (ABCDEFGH)$$. Another same charge $$q$$ is placed at a distance $$L$$ from $$O$$, then the electric flux through $$ABCD$$ is
1063343_fab7238f77a341df871aacd45d7dae1f.png
  • $$\dfrac {q}{4\pi \epsilon_{0}L}$$
  • Zero
  • $$\dfrac {q}{2\pi \epsilon_{0}L}$$
  • $$\dfrac {q}{3\pi \epsilon_{0}L}$$
Find the electric field vector at P(a, a, a) due to three infinitely long lines of charges along the x-, y- and z-axes, respectively. The charge density, i.e., charge per unit length of each wire is $$\lambda$$ :
154767_002b34fe67d44ad8b98c870a30ee8b14.png
  • $$\displaystyle \frac{\lambda}{3 \pi \varepsilon_0 a} (\widehat i + \widehat j + \widehat k)$$
  • $$\displaystyle \frac{\lambda}{2 \pi \varepsilon_0 a} (\widehat i + \widehat j + \widehat k)$$
  • $$\displaystyle \frac{\lambda}{2 \sqrt{2} \pi \varepsilon_0 a} (\widehat i + \widehat j + \widehat k)$$
  • $$\displaystyle \frac{\sqrt{2} \lambda}{\pi \varepsilon_0 a} (\widehat i + \widehat j + \widehat k)$$
A closed surface $$S$$ is constructed around a conducting wire connected to a battery and a switch. As the switch is closed, the free electrons in the wire start moving along the wire. In any time interval, the number of electrons entering the closed surface $$S$$ is equal to the number of electrons leaving it. On closing the switch, the flux of the electric field through the closed surface (more than one option may be correct)
195250_26e4cc4bad4848dbb9e1427a2a475fe6.png
  • is increased
  • is decreased
  • remains unchanged
  • remains zero
A conic surface is placed in a uniform electric field E as shown in Fig. such that the field is perpendicular to the surface on the side AB. The base of the cone is of radius R, and the height of the cone is h. The angle of the cone is $$\theta  $$. Find the magnitude of the flux that enters the cone's curved surface from the left side. Do not count the outgoing flux $$(\theta  < 45^{\circ})$$ :
159079_365acdae62f045ecac7c3dc230938004.png
  • $$ER[h \cos \theta + \pi(R/2) \sin \theta ] $$
  • $$ER[h \sin \theta + \pi R/2 \cos \theta ] $$
  • $$ER[h \cos \theta + \pi R \sin \theta ] $$
  • none of these
Two point charges $$Q_1$$ and $$Q_2$$ are positioned at points $$1$$ and $$2$$, The field intensity to the right of the charge $$Q_2$$ on the line that passes through the two charges varies according to a law that is represented schematically in the figure. 
The field intensity is assumed to be positive if its direction coincides with the positive direction on the $$x-axis$$.The distance between the charges is $$l$$. Find the sign of each charge.

223324_e8d7666decb44a9ead0f2b79a2f7ecdc.png
  • $$Q_2$$ is positive and $$Q_1$$ is negative
  • $$Q_2$$ is positive and $$Q_1$$ is positive
  • $$Q_2$$ is negative and $$Q_1$$ is negative
  • $$Q_2$$ is negative and $$Q_1$$ is positive
Find the net force acting on the dipole.

223761.jpg
  • $$\displaystyle \frac{\partial qQ}{2 \pi \varepsilon_0} \frac{R^2 - 2x^2}{(R^2 + x^2)^{5/2}}$$
  • $$\displaystyle \frac{\partial qQ}{2 \pi \varepsilon_0} \frac{R^2 + 2x^2}{(R^2 + x^2)^{5/2}}$$
  • $$\displaystyle \frac{\partial qQ}{2 \pi \varepsilon_0} \frac{R^2 - 2x^2}{(R^2 - x^2)^{5/2}}$$
  • $$\displaystyle \frac{\partial qQ}{2 \pi \varepsilon_0} \frac{R^2 + 2x^2}{(R^2 - x^2)^{5/2}}$$
The cube as shown in Fig. has sides of length $$L = 10.0\ cm$$. The electric field is uniform, has a magnitude $$E = 4.00\times 10^{3} NC^{-1}$$, and is parallel to the $$xy - plane$$ at an angle of $$37^{\circ}$$ measured from the $$+x-axis$$ towards the $$+y-axis$$.
Electric flux passing through surface $$S_{1}$$ is 
160276_5a01306a38544ae184370fb405ab9d7b.png
  • $$-24 Nm^{2} C^{-1}$$
  • $$24 Nm^{2} C^{-1}$$
  • $$32 Nm^{2} C^{-1}$$
  • $$-32 Nm^{2} C^{-1}$$
The diagram shows the cross-section of a sheet that is infinitely long in the $$x$$ and $$z$$ directions. The sheet has a height $$2D$$ in the $$y$$-direction. The charge carried by the sheet is NOT uniform; the charge density varies according to the equation $$=By$$.
Which of the following expressions gives the electric field strength at point $$P$$, a point that lies within the sheet and is located at $$y=d$$?
495959_fbb76c76ffc0432a905b0c3b315145e2.png
  • $$\cfrac{BD^2}{2{\epsilon}_0}$$
  • $$\cfrac{Bd^3}{3{\epsilon}_0}$$
  • $$\cfrac{BD^3}{3{\epsilon}_0}$$
  • $$\cfrac{Bd^2}{2{\epsilon}_0}$$
  • The electric field is undefined because the sheet carries an infinite amount of charge.
Two point charges $$+q$$ and $$-4q$$ are placed at $$(-a, 0)$$ and $$(+a, 0)$$. Take electric field intensity to be positive if it is along positive $$x-$$direction. The variation of the electric field intensity as one moves along the $$x-$$axis is: 
In fig., a cone lies in a uniform electric field E. Determine the electric flux entering the cone.
161145_2d99df7b08a8452c941a8df980705a83.png
  • Flux $$\phi=EA=2ERh$$
  • Flux $$\phi=EA=7ERh$$
  • Flux $$\phi=EA=9ERh$$
  • Flux $$\phi=EA=ERh$$
Two parallel large thin metal sheets have equal surface charge densities $$\displaystyle \left( \sigma =26.4\times { 10 }^{ -12 }{ c }/{ { m }^{ 2 } } \right) $$ of opposite signs.
The electric field between these sheets is:
  • $$\displaystyle 1.5N/C$$
  • $$\displaystyle 1.5\times { 10 }^{ -10 }{ N }/{ C }$$
  • $$\displaystyle 3N/C$$
  • $$\displaystyle 3\times { 10 }^{ -10 }{ N }/{ C }$$
Two infinitely long parallel conducting plates having surface charge densities $$\displaystyle +\sigma $$ and $$\displaystyle -\sigma $$ respectively, are separated by a small distance. The medium between the plates is vacuum. If $$\displaystyle { \varepsilon  }_{ 0 }$$ is the dielectric permittivity of vacuum then the electric field in the region between the plates is: 
  • 0 volt/m
  • $$\displaystyle { \sigma }/{ 2{ \varepsilon }_{ 0 } }$$ volt/m
  • $$\displaystyle { \sigma }/{ { \varepsilon }_{ 0 } }$$ volt/m
  • $$\displaystyle 2{ \sigma }/{ { \varepsilon }_{ 0 } }$$ volt/m
0:0:1


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