CBSE Questions for Class 12 Medical Physics Electric Charges And Fields Quiz 8 - MCQExams.com

Two charges $$+20\mu C$$ and $$-20\mu C$$ are placed $$10mm$$ apart. The electric field at point $$P$$, on the axis of the dipole $$10cm$$ away from its centre $$O$$ on the side of the positive charge is
941055_6dc112a980eb43b4b3a8de9d5d5c9c69.PNG
  • $$8.6\times { 10 }^{ 9 }N\quad { C }^{ -1 }$$
  • $$4.1\times { 10 }^{ 6 }N\quad { C }^{ -1 }$$
  • $$3.6\times { 10 }^{ 6 }N\quad { C }^{ -1 }$$
  • $$4.6\times { 10 }^{ 5 }N\quad { C }^{ -1 }$$
Which of the following statements about dipole moment is not true ?
  • The dimension of dipole moment is $$\left[ LTA \right] $$
  • The unit of dipole moment is $$C$$ $$m$$
  • Dipole moment is vector quantity and directed from negative to positive charge
  • Dipole moment is a scalar quantity and has magnitude charge equal to the potential of separation between charge
The electric field intensity at a point $$P$$ due to point charge $$q$$ kept at point $$Q$$ is $$24N{ C }^{ -1 }$$ and the electric potential at point is $$12J{ C }^{ -1 }$$. The order of magnitude of charge $$q$$ is
  • $${ 10 }^{ -6 }C$$
  • $${ 10 }^{ -7 }C$$
  • $${ 10 }^{ -10 }C$$
  • $${ 10 }^{ -9 }C$$
Choose the correct answer from the alternatives given.
If $$\varepsilon_0$$ and $$\mu_0$$ are respectively the electric permittivity and the magnetic permeability of free space and $$\varepsilon$$ and $$\mu$$ the corresponding quantities in a medium, the refractive index of the medium is
  • $$\sqrt{\dfrac{\mu\varepsilon}{\mu_0 \varepsilon_0}}$$
  • $$\dfrac{\mu\varepsilon}{\mu_0 \varepsilon_0}$$
  • $$\sqrt{\dfrac{\mu_0\varepsilon_0}{\mu\varepsilon}}$$
  • $$\dfrac{\mu\mu_0}{\varepsilon\varepsilon_0}$$
The electric field and the  potential of an electric dipole vary with distance $$r$$ as
  • $$\cfrac{1}{r}$$ and $$\cfrac { 1 }{ { r }^{ 2 } } $$
  • $$\cfrac { 1 }{ { r }^{ 2 } } $$ and $$\cfrac{1}{r}$$
  • $$\cfrac { 1 }{ { r }^{ 2 } } $$ and $$\cfrac { 1 }{ { r }^{ 3 } } $$
  • $$\cfrac { 1 }{ { r }^{ 3 } } $$ and $$\cfrac { 1 }{ { r }^{ 2 } } $$
Figure shows electric field lines in which an electric dipole $$\vec { P } $$ is placed as shown.
Which of the following statements is correct?
941686_8fded3231e8143fcba29818c8ac63b6c.png
  • The dipole will not experience any force
  • The dipole will experience a force towards right
  • The dipole will experience a force towards left
  • The dipole will experience a force upwards
Which of the following is not true?
  • For a point charge, electrostatic potential varies as $$\dfrac { 1 }{ r }$$.
  • For a dipole, the potential depends on the magnitude of position vector and dipole moment vector.
  • The electric dipole potential varies as $$\dfrac { 1 }{ r }$$ at large distance.
  • For a point charge, the electrostatic field varies as $$\dfrac { 1 }{{ r }^{ 2 }}$$.
When air is replaced by a dielectric medium of constant K, the maximum force of attraction between two charges separated by a distance:
  • increases K times
  • remains unchanged
  • decreases K times
  • increases $${ K }^{ -1 }$$ times
Choose the correct statement
  • Polar molecules have permanent electric dipole moment
  • $${CO}_{2}$$ molecule is a polar molecule
  • $${H}_{2}O$$ is a non-polar molecule
  • The dipole field at large distances falls of as $$\cfrac { 1 }{ { r }^{ 2 } } $$
Which among the following is an example of polar molecule?
  • $${ O }_{ 2 }$$
  • $${ H }_{ 2 }$$
  • $${ N }_{ 2 }$$
  • HCl
Two large thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and magnitude $$27\times { 10 }^{ -22 }C\quad { m }^{ -2 }$$. The electric field   $$\vec { E } $$ in region II in between the plates is
941270_2a11cb97bb5f48718b234f90bb4a67f7.PNG
  • $$4.25\times { 10 }^{ -8 }N\quad { C }^{ -1 }\quad $$
  • $$6.28\times { 10 }^{ -10 }N\quad { C }^{ -1 }$$
  • $$3.05\times { 10 }^{ -10 }N\quad { C }^{ -1 }$$
  • $$5.03\times { 10 }^{ -10 }N\quad { C }^{ -1 }$$
Two conducting and concentric thin spherical shells or radii $$a$$ and $$b,\,\left( {b > a} \right)$$ have charges $${q_1}$$ and $${q_2}$$ respectively. Now if the inner shell is earthed then the final charge on this shell will be
  • $$\dfrac{{{q_2}{a^2}}}{{{b^2}}}$$
  • $$\dfrac{{ - {q_2}a}}{b}$$
  • $$\dfrac{{\left( {{q_1} + {q_2}} \right)}}{2}$$
  • $$ - \dfrac{{{q_2}b}}{a}$$
A uniform line charge with linear density $$\lambda$$ lies along the y-axis. What flux crosses a spherical surface centred at he origin with $$r\ =\ R$$
  • $$\large{\frac{2R\lambda}{\epsilon_0}}$$
  • $$\large{\frac{R\lambda}{\epsilon_0}}$$
  • $$\large{\frac{\lambda}{\epsilon_0}}$$
  • none of the above
The electric field of a radio wave is given by $$\vec{E} = E sin (Kz - \omega t) (\hat{i} + \hat{j})$$ . Give a unit vector
in the direction of the magnetic field at a place and time where sin$$(kz - \omega t)$$ is positive.
  • $$(\hat{i}^ + \hat{k}) / \sqrt{2}$$
  • $$(-\hat{i} - \hat{k} / \sqrt{2}$$
  • $$-\hat{i} + \hat{j} / \sqrt{2}$$
  • $$\hat{i} - \hat{j} / \sqrt{2}$$
Two concentric spherical shells of radii R and $$2$$R have charges $$+$$Q and $$-$$Q. Which of the following may represent correct variation of potential with distance r from origin?
Two equal point charges are fixed at $$x=-a$$ and $$x=+a$$ on the $$x-$$axis. Another point charge $$Q$$ is placed at the origin. The change in the electrical potential energy of $$Q$$, when it is displaced by a small distance $$x$$ along the $$x-$$axis, is approximately proportional to:
  • $$x$$
  • $$x^{2}$$
  • $$x^{3}$$
  • $$\dfrac{1}{x}$$
A rectangular surface of sides 10 cm and 15 cm is placed inside a uniform electric field of 25 V/m, such that the surface makes an angle $$30^{\circ}$$ with the direction of electric field. Find the flux of the electric field  through the rectangular surface 
  • $$0.1675\ \ N m^2/C$$
  • $$0.1875\ \ N m^2/C$$
  • $$Zero$$
  • $$0.1075\ \ N m^2/C$$
Consider an electric field $$\bar { E } =E_{ 0 }\hat { x }$$ where $$E_{0}$$ is a constant. The flux through the shaded area (as shown in the figure) due to this field is
1010537_3586de4a6fd8414cbc48e9028b80b378.png
  • $$2E_{0}a^{2}$$
  • $$\sqrt{2}E_{0}a^{2}$$
  • $$E_{0}\ a^{2}$$
  • $$\dfrac{E_{0}a^{2}}{\sqrt{2}}$$
the point $$P$$, the flux of the electric field through the closed surface:
1023705_7885fe05925449c5846d65bc7ef34541.png
  • will remain zero
  • will becomes positive
  • will become negative
  • will become undefined
If the intensity of electric field at a distance $$x$$ from the centre in axial position of small electric dipole is equal to the intensity at a distance $$y$$ in equatorial position, then
  • $$x = y$$
  • $$x = y/2$$
  • $$y = x/2^{2/3}$$
  • $$y = x/2^{1/3}$$

Three charge +4q, Q and q are placed in a straight line of length $$l$$ at points distance 0, $$\dfrac{l}{2}$$ and $$l$$ respectively. What should be the value of Q in order to make the net force on q to be zero?
  • $$-q$$
  • $$-2q$$
  • $$-q/2$$
  • $$4q$$

A solid insulating sphere of radius a carries a net positive charge 3Q, uniformly Distributed throughout its volume. Concentric with this sphere is a conducting Spherical shell with inner radius b and outer radius c and having a net charge Q, As shown in the figure.Electric field varies with distance r from the centre as  $$\left( {K = {1 \over {4\pi {\varepsilon _o}}}} \right)$$


1018911_3754aa6cbbe34d459724e55a9d23faf1.PNG
A charge situated at a certain from an electric dipole (small), in the end on position, experience a force $$F$$. Find the force acting on the same charge due to same dipole if its distance from the centre of dipole is doubled.
  • $$F/8$$
  • $$F/4$$
  • $$3F/8$$
  • $$F/2$$

 A point charge Q is placed at origin O. Let $$\overrightarrow {{E_A}} $$,$$\overrightarrow {{E_B}} $$ and $$\overrightarrow {{E_C}} $$ represent electric fields at A, B and C respectively. If coordination of A,B and C are respectively (1,2,3) m,(1,1,-1) m and (2,2,2) m  then 
  • $$\overrightarrow {{E_A}} \bot \overrightarrow {{E_B}} $$
  • $$\overrightarrow {{E_A}} \parallel \overrightarrow {{E_B}} $$
  • $$\left| {\overrightarrow {{E_B}} } \right|\parallel 4\left| {\overrightarrow {{E_C}} } \right|$$
  • $$\left| {\overrightarrow {{E_B}} } \right|\parallel 8\left| {\overrightarrow {{E_C}} } \right|$$
A point charge is placed at the corner of a cube. The electric flux through the shaded surface is 
1019651_e34ec158f02c4fa2b3e4110f066ed20f.png
  • $${q \over {8{\varepsilon _0}}}$$
  • $${q \over {{\varepsilon _0}}}$$
  • $${q \over {24{\varepsilon _0}}}$$
  • $${q \over {12{\varepsilon _0}}}$$
A charge $$Q$$ is divided into two parts of $$q$$ and $$Q-q$$. If the Coulomb repulsion between them when they are separated, is to be maximum, the ratio of $$\dfrac{Q}{q}$$ should be:
  • $$2$$
  • $$1/2$$
  • $$4$$
  • $$1/4$$
Charge Q is uniformly distributed over a ring of radius r .Electric field at a point on the axis is maximum at a distance x from the centre. x is equal to
  • $$\dfrac{r}{\sqrt 2}$$
  • $$\dfrac{r} {2}$$
  • $$\sqrt 2 r$$
  • $$r$$
The total electric flux through a cube when a charge $$8q$$ is placed at one corner of the cube is
  • $${ \varepsilon }_{ 0 }q$$
  • $$\dfrac { { \varepsilon }_{ 0 } }{ q }$$
  • $$4\pi { \varepsilon }_{ 0 }q$$
  • $$\dfrac { q }{ { \varepsilon }_{ 0 } }$$
A square of side 'a' is lying in xy plane that two of its sides are lying on the axis. If $$\vec{E} = E_0 x \hat{k}$$ is applied on the square. The flux passing through the square is
  • $$E_0 a^2$$
  • $$\dfrac{E_0 a^3}{2}$$
  • $$\dfrac{E_0 a^3}{3}$$
  • $$\dfrac{E_0 a^2}{2}$$
The ratio of the electric force between two proton to that between two electrons under similar conditions is the order of:
  • $$10^{42}$$
  • $$10^{39}$$
  • $$10^{36}$$
  • $$1$$
A point charge $$+q$$ is placed at the centre of a cube of side $$L$$. The electric flux emerging from the cube is
  • $$\cfrac{q}{{ \varepsilon }_{ 0 }}$$
  • zero
  • $$\cfrac{6q{L}^{2}}{{ \varepsilon }_{ 0 }}$$
  • $$\cfrac{q}{6{L}^{2}{ \varepsilon }_{ 0 }}$$

The chasrge density of an insulating infinity surface is $$\left( {e/\pi } \right)\;c{m^2}$$ then the field intensity at a nearby point in volt/meter will be -
  • $$2.88 \times {10^{ - 12}}$$
  • $$2.88 \times {10^{ - 10}}$$
  • $$2.88 \times {10^{ - 9}}$$
  • $$2.88 \times {10^{ - 18}}$$
Which of the following aren't the properties of lines of force of an electric field?

  1. Lines of force always intersect.
  2. Lines of force start from negative charge and terminate at te positive charge.
  3. The tangent to line of force at a point gives the direction of the electric field.
  4. Each unit positive charge gives rise to $$ 1 / 4 \pi \epsilon_0 $$ lines of force in free space.
  • 1 and 2
  • 2 and 4
  • 1 and 3
  • 2 and 3
A charged particle $$q$$ is projected in an electric field produced by a fixed point charge $$Q$$ as shown in the figure. Select the correct statements:

1031218_a22b5b192c5f466f902b7a4846a4d74c.png
  • The path taken by $$q$$ is a straight line
  • The path taken by $$q$$ is not a straight line
  • The minimum distance between the two particle is $$\dfrac{\dfrac{qQ}{2\pi\varepsilon_{0}}+\sqrt{\left(\dfrac{qQ}{2\pi\varepsilon_{0}}\right)^{2}+4m^{2}u^{2}a^{2}}}{2mu^{2}}$$
  • Velocity of the particle $$q$$ is changing in both magnitude and direction.
The work done by an external force in rotating dipole of dipole moment $$\vec{P}$$ slowly in uniform electric field of intensity $$\vec{E}$$ from $$0^0$$ to $$180^0$$
  • $$\text{2 PE}$$
  • $$\text{8 PE}$$
  • $$\text{9 PE}$$
  • $$\text{5 PE}$$
A charged oil drop od mass $$ 2.5\times { 10 }^{ -7 } kg$$ is in space between the two plates, each of area $$ 2\times { 10 }^{ -2 } { m }^{ 2 }$$ of a parallel plate capacitor. When the upper plate has a charge of $$ 5\times { 10 }^{ -7 } C$$ and the lower plate has an equal negative charge then the oil remains stationery. The charge of the oil drop is (take, $$g=10 { m/s }^{ 2 }$$)
  • $$ 9\times { 10 }^{ -1 } C$$
  • $$ 9\times { 10 }^{ -6 } C$$
  • $$ 8.85\times { 10 }^{ -13 } C$$
  • $$ 1.8\times { 10 }^{ -14 } C$$
What is the angle between the electric dipole moment and the electric field strength due to it on the equatorial line?
  • $$0^o$$
  • $$90^o$$
  • $$180^o$$
  • none of these
The line integral of an electric field along the circumference of a circle of radius r drawn with a point Q at the centre will be _____
  • $$\dfrac{1}{4 \pi^2 to } \dfrac{Q}{r}$$
  • $$\dfrac{Q}{2 \pi \varepsilon_0 r}$$
  • Zero
  • $$2 \pi Q r$$
Shown below is a distribution of charges. The flux of electric field due to these charges through the surface S is
1070813_55d14bfa955c41ac8900c98bb48d9c1a.png
  • $${3q/\epsilon_o}$$
  • $${2q/\epsilon_o}$$
  • $${q/\epsilon_o}$$
  • zero
At a certain distance from a point charge the electric field is $$500\ V/m$$ and the potential is $$3000\ V$$. What is this distance:
  • $$36\ m$$
  • $$12\ m$$
  • $$6\ m$$
  • $$144\ m$$
In the figure shown here, A is a conducting sphere and B is a closed spherical surface. If a-q change is placed at C near A, then the electric flux through the closed surface is -
1083017_f13c4074e7854fc5b31b25c3d21902ef.PNG
  • zero
  • positive
  • negative
  • none of the above can be predicted
An electron (of charge $$-e$$) revolves around a long wire with uniform charge density $$\lambda$$ in a circular path of radius $$r$$. Its kinetic energy is given by:
  • $$\dfrac { \lambda e }{ 8\pi { \epsilon }_{ 0 }r }$$
  • $$\dfrac { \lambda e }{ 4\pi { \epsilon }_{ 0 }r }$$
  • $$\dfrac { \lambda e }{ 2\pi { \epsilon }_{ 0 }r}$$
  • $$\dfrac { \lambda e }{ 4\pi { \epsilon }_{ 0 } }$$
The figure shows a family of equipotential surfaces and four paths along which an electron is made to move from one surface to another as shown in figure.
1) What is the direction of electric field?
2) Rank the paths according to the magnitude of the work done, greatest first
1075503_4a70f4a3e0e14821a8e280cc5e521736.png
  • $$Rightward ; 4 > 3 > 2 > 1$$
  • $$Leftward ; 1 > 2 > 3 > 4$$
  • $$Rightward ; 3 = 4 > 2 = 1$$
  • $$Leftward ; 1 > 2 > 3 = 4$$
A plane surface of area $$10\ cm^{2}$$ is placed in a uniform electric field of $$20\ N/C$$ such that the angle between the surface and the electric field is $$30^{o}$$. The electric flux over the surface is:
  • $$0.0173\ Vm$$
  • $$0.0236\ Vm$$
  • $$0.01\ Vm$$
  • $$0.0346\ Vm$$
A point charge of value $$10^{-7}\ C$$ is situated at the centre of cube of $$1\ m$$ side. The electric flux through its total surface area is:
  • $$113\times 10^{4}\ Nm^{2}/C$$
  • $$11.3\times 10^{4}\ Nm^{2}/C$$
  • $$1.13\times 10^{4}\ Nm^{2}/C$$
  • $$none\ of\ these$$
A  wire of linear charge density $$\lambda$$ passes through a cuboid of length $$\ell$$, breadth $$b$$ and height $$h\ (\ell>b>h)$$ in such a manner that flux through the cuboid is maximum. The position of the wire is now changed, so that the flux through the cuboid is minimum. The ratio of maximum flux to minimum flux will be :
  • $$\dfrac{\sqrt{l^{2}+b^{2}}}{h}$$
  • $$\dfrac{\sqrt{l^{2}+b^{2}+h^{2}}}{h}$$
  • $$\dfrac{h}{\sqrt{l^{2}+b^{2}}}$$
  • $$\dfrac{l}{\sqrt{l^{2}+b^{2}+h^{2}}}$$
A point charge of $$+6\mu C$$ is placed at a distance 20 cm directly above the centre of a square of side 40 cm. The magnitude of the flux through the square is
  • $$\epsilon_0$$
  • $$\dfrac{1}{\epsilon_0}$$
  • $$\epsilon_0\times 10^{-6}$$
  • $$\dfrac{1}{\epsilon_0} \times 10^{-6}$$
If the dipole is place in a non-uniform electric field an angle $$\theta$$, in addition tarque 
  • Experiences a force
  • Experiences a repulsive force
  • No any kind of force
  • Neither attractive nor repulsive force
There are two charges $$+2\mu\ C\ and -3\mu\ C$$. The ratio of forces acting on them will be 
  • $$2:3$$
  • $$1:1$$
  • $$3:2$$
  • $$4:9$$
A charge q is to be distributed on two conducting spheres. What should be the value of the charges on the spheres so that the repulsive force between them is maximum when they are placed at a fixed distance from each other in air?
  • $$\dfrac{q}{2}$$ and $$\dfrac{q}{2}$$
  • $$\dfrac{q}{4}$$ and $$\dfrac{3q}{4}$$
  • $$\dfrac{q}{3}$$ and $$\dfrac{2q}{3}$$
  • $$\dfrac{q}{5}$$ and $$\dfrac{4q}{5}$$
0:0:1


Answered Not Answered Not Visited Correct : 0 Incorrect : 0

Practice Class 12 Medical Physics Quiz Questions and Answers