CBSE Questions for Class 12 Medical Physics Electric Charges And Fields Quiz 9 - MCQExams.com

A charge $$+q$$ having mass $$m$$ is released from rest in a uniform electric field $$E$$ momentum acquired by the charge after time $$t$$ is:
  • $$\frac{{{q^2}{E^2}{t^2}}}{{2m}}$$
  • $$\dfrac{q Et}{m}$$
  • $$q Et$$
  • None of these.
When a glass rod is rubbed with a piece of silk cloth the rod acquires
  • positive charge
  • negative charge
  • both positive and negative charge
  • no charge
For a dipole, the value of each charge is $$10^{-10}\ stat\ coulomb$$ and separation is $$1A^0$$, then its dipole moment is :
  • $$1 debye$$
  • $$2 debye$$
  • $$10^{-3} debye$$
  • $$3\ \times\ 10^{-20} debye$$
An extremely long wire is uniformly charged. An electron is revolving around the wire and making $${ 10 }^{ 8 }$$ revolutions per second in an orbit of radius $$2cm$$. Linear charge density of the wire is nearly ?
  • $$50 nC/m$$
  • $$25 nC/m$$
  • $$40 nC/m$$
  • $$12.5 nC/m$$
Charges $$\theta_1$$ and $$\theta_2$$ lie inside and out side respectively for a closed surface s. Let E be the field at a point on S and $$\phi$$ be flux of E over S
  • If only $$\theta_1$$ changes, both E & $$\phi$$ charges
  • If only $$\theta_2$$ changes, E will change but $$\phi$$ will not change
  • If $$\theta_1=0, \theta_2\neq 0$$ then $$E \neq 0$$ but $$\phi = 0$$
  • If $$\theta_1=0, \theta_2\neq 0$$ then $$E = 0$$ but $$\phi \neq 0$$
A point charge $$q$$ is placed at a distance $$\dfrac {a}{2}$$ above the center of a square surface of side $$a$$. The electric flux through the square is:-
  • $$\dfrac {q}{\epsilon_{0}}$$
  • $$\dfrac {q}{\pi\ \epsilon_{0}}$$
  • $$\dfrac {q}{4\ \epsilon_{0}}$$
  • $$\dfrac {q}{6\ \epsilon_{0}}$$
An electron enters an electric field with its velocity in the direction of the electric lines of field then:
  • the path of the electron will be a circle
  • the path of the electron will be a parabola
  • the velocity of the electron will decrease just after entry
  • the velocity of the electron will increase just after entry
In a region of space, the electric field is given by $$\vec {E} = 8\hat {j} + 4\hat {j} + 3\hat {k}$$. The electric flux through a surface of area of $$100$$ units in $$x - y$$ plane is?
  • $$800\ units$$
  • $$300\ units$$
  • $$400\ units$$
  • $$1500\ units$$
Force of interaction between two co-axial short electric dipoles whose centres are R distance apart varies as :
  • $$\frac{1}{R}$$
  • $$\frac{1}{R^{2}}$$
  • $$\frac{1}{R^{3}}$$
  • $$\frac{1}{R^{4}}$$
The electric potential is directly proportional to from the region. The intensity of electric field  
  • Is proportional to $$r^{2}$$
  • Is changing with uniform rate
  • Is uniform
  • Is non-uniform
A small ball of mass m carrying a charge of Q is dropped in a uniform horizontal magnetic field B . Depth of deepest point of its path from point release is h. choose the correct  option:
  • Speed at deepest point is $$\sqrt { 2gh } $$
  • Speed at deepest point is $$\frac { QBh }{ m } $$
  • Speed at deepest point is $$\frac { 2mg }{ QB} $$
  • Speed at deepest point is $$\frac { 2QBh }{ m} $$
A particle of mass $$m$$ and charge $$+q$$ approaches from a very large distance towards a uniformly charged ring of radius $$R$$ and charge, mass same as that of particle, with initial velocity $$v_0$$ along the axis of the as shown in the figure. What is the closet distance of approach between the ring and the particle? Assume the space to be gravity free and frictionless.
1130904_04705a88e1d4443d90e09b7186bbd1e0.PNG
  • $$\sqrt{\dfrac{q^4}{\pi^2 \varepsilon_{0}^{2} m^2 v_{0}^{2}} - R^2}$$
  • $$\sqrt{\dfrac{3q^4}{2\pi^2 \varepsilon_{2}^{0} m^2 v_{4}^{0}} - R^2}$$
  • $$\sqrt{\dfrac{m^2 v_{4}^{0}}{2\pi^2 q^4 \varepsilon_{2}^{0}} - R^2}$$
  • $$\sqrt{\dfrac{q^4}{4\pi^2 \varepsilon_{2}^{0} m^2 v_{4}^{0}} - R^2}$$
A particle of mass $$m$$ and positive charge $$q$$ is projected towards an infinitely long line of a charge (having linear density of charge $$+\lambda$$) from a distance $$t_0$$. The direction of initial velocity $$v_0$$ makes an angle $$30^\circ$$ with the normal to the line of charge as shown in figure. The minimum distance of approach of the charge particle with the line of charge will be (neglect gravity). Take $$\lambda = \dfrac{\pi \varepsilon_0 mv_0^2}{4q}$$.
1130874_244986dcdd844a95b229a0c484578aba.png
  • $$\dfrac{r_0}{e}$$
  • $$\dfrac{r_0}{e^2}$$
  • $$\dfrac{r_0}{e^3}$$
  • $$\dfrac{r_0}{2}$$
The electric field at a point is:
  • Always continuous
  • Continuous if there is no charge at that point.
  • Discontinuous only if there is a negative charge at that point.
  • Discontinuous if there is a charge at that point.
A point charge + Q is positioned at the centre of the base of square pyramid as shown. The flux through one of the four identical upper faces of the pyramid is
1130169_2ecf66a54e774f76895d1a51f595ccf1.png
  • $$Q/16\varepsilon_0 $$
  • $$Q/4\varepsilon_0 $$
  • $$Q/8\varepsilon_0 $$
  • none
The electric dipole moment of an electron and a proton $$4.3\ nm$$ apart is
  • $$6.88\times 10^{-28}Cm$$
  • $$2.56\times 10^{-29} C^{2}/ m$$
  • $$3.72\times 10^{-14} C/m$$
  • $$13.76\times 10^{-29} C^{2}/m$$
A charged body has an electric flux F associated with it . Now if the body is place inside a conducting shell then the electric flux outside the shell is:
  • zero
  • Greater than F
  • Less than F
  • Equal to F
Two coaxial coils are very close to each other and their mutual inductance is $$5$$ mH. If a current $$50\sin 500r$$ is passed in one of the coils then the peak value of induced e.m.f. in the secondary coil will be?
  • $$5000$$V
  • $$500$$V
  • $$150$$V
  • $$125$$V
Two conducting spheres of radii $$r_!$$ and $$r_2$$ have same electric field near their surfaces. The ratio of their electric potentials is :-
  • $$r_1^2 / r_2^2$$
  • $$r_2^2 / r_1^2$$
  • $$r_1 / r_2$$
  • $$r_2 / r_1$$
Eight point charges (can be assumed as small spheres uniformly charged and their centres at the corner of the cube) having values q each are fixed at vertices of a cube. The electric flux through square surface ABCD of the cube is 

1185561_7f93b1565130410fafd5b36ff82f900d.PNG
  • $$\frac {q}{24 \in_0}$$
  • $$\frac {q}{12 \in_0}$$
  • $$\frac {q}{6 \in_0}$$
  • $$\frac {q}{8 \in_0}$$
Following figure shows four situations in which positive and negative charges moves horizontally through a region and gives the rate at which each charge moves. Rank the situations according to the effective current through the region greatest first 
1204721_d26f7cee63b14da6ae6546098d7b1083.png
  • $$i = i i = i i i = i v$$
  • $$i > i i > i i i > i v$$
  • $$i = i i = i i i > i v$$
  • $$i = i i = i i i < i v$$
 A molecule with a dipole moment p is placed in electric field of strength E. Initially the dipole is aligned parallel to the field. If the dipole is to be rotated to be anti parallel to the field, the work required to be done by an external agency is 
  • -2pE
  • -pE
  • pE
  • 2pE
Electric ield on the axis of small electric dipole at a distance r is $$\vec{E_1}$$ and $$\vec{E_2}$$ at a distance $$2$$r on a line of perpendicular dissector. Then
  • $$\vec{E_2}=-\dfrac{\vec{E_1}}{8}$$
  • $$\vec{E_2}=-\dfrac{\vec{E_1}}{16}$$
  • $$\vec{E_2}=-\dfrac{\vec{E_1}}{4}$$
  • $$\vec{E_2}=\dfrac{\vec{E_1}}{8}$$
An electron at rest has a charge of $$1.6\ \times 10^{-19}\ C$$. It starts moving with a velocity $$v=c/2$$, where $$c$$ is the speed of light, then the value the new charge on it is-
  • $$1.6\ \times 10^{-19}$$ Coulomb
  • $$1.6\ \times 10^{-19}\sqrt {1-\left(\dfrac {1}{2}\right)^{2}}$$ Coulomb
  • $$1.6\ \times 10^{-19}\sqrt {\left(\dfrac {1}{2}\right)^{2}-1}$$ Coulomb
  • $$\dfrac {1.6\ \times 10^{-19}}{\sqrt {1-\left(\dfrac {1}{2}\right)^{2}}}$$ Coulomb
An infinite cylinder of radius 'R' carrying charge density . $$ p = ar +br^{2}$$ where 'r' distance of point from the axis and a b are non-zero constant. Find the ratio of a/b if field out of the cylinder is zero
  • $$\frac{R}{4}$$
  • -$$\frac{R}{4}$$
  • -$$\frac{3R}{4}$$
  • $$\frac{3R}{4}$$
Three charger $$q. Q$$ and $$4q$$ are placed in a straight, line of length $$L$$ at points distant $$0, L/2$$ and $$L$$ respectively from one end in other to make the net force on $$q$$ zero the charge $$Q$$ must be eqyal to:
  • $$-q$$
  • $$2q$$
  • $$-\dfrac{q}{2}$$
  • $$q$$
Two charged plates with charges $$Q$$ and $$3Q$$ are placed $$d$$ distance apart. Another plate with charge $$Q$$ is placed between two plates.
Final charges $$q_{3}$$ and $$q_{5}$$ on the surface of plates are 
  • $$\dfrac{-Q}{2},\dfrac{-3Q}{2}$$
  • $$\dfrac{-Q}{2},\dfrac{-5Q}{2}$$
  • $$\dfrac{-3Q}{2},\dfrac{-5Q}{2}$$
  • $$\dfrac{-3Q}{2},\dfrac{-3Q}{2}$$
8 four  point  charge of + $$10^{-7}C,-10^{-7},C,-2\times 10^{-7}$$C and + $$2\times 10^{-7}$$ are placed respectively at the corner A, B,C, of a 0.05 m square. Find the magnitude of the resultant force on the charge at D.
  • 0.2 dyne
  • 0.2 newton
  • 2 dyne
  • 0.02 newton
A charge +Q is located in space at point $$(x=1 m,y=10m, z=5m)$$. What is the total electric flux that passes through the $$y-z$$ plane?
  • $$\cfrac Q {\varepsilon_0}$$
  • $$\cfrac Q {3\varepsilon_0}$$
  • $$\cfrac Q {6\varepsilon_0}$$
  • $$\cfrac Q {2\varepsilon_0}$$
Flux through the rectangular piece of area 10 cm by 20 cm when placed ( as shown in an uniform electric field of 200 N/C, ) is 
1226258_6c915fa072fe4b64bad429f1ef6bb3ef.png
  • 4.0 $$Nm^{2}/C$$
  • 3.5 $$Nm^{2}/C$$
  • 2.5 $$Nm^{2}/C$$
  • zero
A dipole of dipole moment P is placed at a distance r form a point change Q(as shown in figure).Choose the incorrect statement.


1229789_3934ccb75e14433b9de6f143c8b28f39.PNG
  • Torque acting on the dipole is zero
  • Force acting on the dipole due to the electrie field produce by Q is zero
  • potential energy of the dipole due to the point charge Q is $$\frac { Qp }{ { 4\pi }{ \varepsilon }_{ 0 }{ r }^{ 2 } } $$
  • Force acting on the dipole due to the point charge Q is $$\frac { Qp }{ { 4\pi }{ \varepsilon }_{ 0 }{ r }^{ 3 } } $$
Figures below show regular hexagons, with charges at the vertices. In which case is the electric filed at the center zero?
1222774_3302fccf4a2948239e20fa056b889264.png
  • $$1$$
  • $$2$$
  • $$3$$
  • $$4$$
Four charges $$+Q,-Q,+Q$$ and $$-Q$$ are situated at the corners of a square; in a sequence then at the centre of the square:
  • $$E=0,V=0$$
  • $$E=0,V\neq 0$$
  • $$E\neq 0,V=0$$
  • $$E\neq 0,V\neq 0$$
To construct an air filled capacitor which can store $$ 12 \mu C $$ of charge, What can be the minimum plate area of the capacitor? (Dielectric strength of air is $$3\times 10^6 V/m$$ )
  • $$0.25 m^2$$
  • $$0.45 m^2$$
  • $$4.5 m^2$$
  • $$0.35 m^2$$
Two equally charged identical metal spheres A and B repel other with a force of $$2 \times {10^{ - 5}}$$.Another identical uncharged sphere C is touched to B and then placed at the mid point between A and B.The net electric force on C is.
  • $$2 \times {10^{ - 5}}\;N\;along\;\overrightarrow {AB} $$
  • $$2 \times {10^{ - 5}}\;N\;along\;\overrightarrow {BA} $$
  • $$4 \times {10^{ - 5}}\;N\;along\;\overrightarrow {AB} $$
  • $$4 \times {10^{ - 5}}\;N\;along\;\overrightarrow {BA} $$
A light beam travelling in the x-direction is described by the electric field $${ E }_{ y }=(300V{ m }^{ -1 })sin\quad \omega (t-x/c).$$ An electron is constrained to move along the y-direction with a speed of $$2.0\times  {10}^7 { m }^{ -1 }$$ Find the maximum electric force and the maximum magnetic force on the electron
  • $$4.8\times {10}^{-17} N, zero$$
  • $$4.2\times {10}^{-18} N, 1.8\times 10^{-8}N$$
  • $$4.8\times {10}^{-17} N, 3.2\times 10^{-18}N$$
  • Zero, Zero
Two charges Q and -2Q are placed at some distance. the locus of points in the plane of the charges where the potential is zero will be
  • Straight line
  • Circle
  • Parabola
  • ellipse
Two or more cells joined together form a...................
  • Dry cell
  • Battery
  • Transformer
  • MCB
The charges 1,2,3 are moving in uniform transverse magnetic field then :-
1255947_93298193a5d64e7ca61570e27e324e02.png
  • Particle 1 positive and particle 3 negative
  • Particle 1 negative and particle 3 positive
  • Particle 1 negative and particle 2 neutral
  • Particle 1 and 3 are positive and particle 2 neutral

A ring of radius R is charged uniformly with a charge +Q. The electric field at a point on its axis at a distance r from any point on the ring will be:-
  • $$\dfrac{{KQ}}{{\left( {{r^2} - {R^2}} \right)}}$$
  • $$\dfrac{{KQ}}{{{r^2}}}$$
  • $$\dfrac{{KQr}}{{{r^3}}}{\left( {{r^2} - {R^2}} \right)^{\dfrac{1}{2}}}$$
  • $$\dfrac{{KQr}}{{{R^3}}}$$
The electrical force is a:
  • contact force
  • force at distance
  • consequential force
  • none of these
The electric field intensity due to a dipole of 10 cm and having a charge of $$500 \mu C$$, on the axis at a distance $$20 cm$$.
  • $$6.25 \times 10^7 N/C$$
  • $$6.28 \times 10^7 N/C$$
  • $$1.31 \times 11^{11} N/C$$
  • $$20.5 \times 10^7 N/C$$
The total probability of finding a particles in space under normalized condition according to quantum mechanics is
  • Zero
  • Infinity
  • One
  • Uncertain
Figure shows an electric line of force which curves along a circular arc. The magnitude of electric field intensity is same at all points on this curve and is equal to E. If the potential at A is V, then the potential at B is: 

1271289_3e042cbf120e4771989e53e912f22e02.PNG
  • $$V-ER\theta$$
  • $$V-2ER sin \dfrac {\theta} {2}$$
  • $$V+ER\theta$$
  • $$V+2ER sin \dfrac {\theta} {2}$$
Which of the following is correct for the case of an uniform electric field?
  • All points are at the same potential
  • No two points can have the same potential
  • Pairs of points separated by the same distance must have the same difference in potential
  • None of the above
A hemispherical surface of radius R is kept in a uniform electric field E as shown in figure. The flux through the curved surface is:
1262233_b5e38ac743674ab0b49cf87466e60cd3.PNG
  • $$E2\pi R^2$$
  • $$E\pi R^2$$
  • $$E4\pi R^2$$
  • $$Zero$$
A small sphere of radius $$ r_1 $$ and charge $$ q_1 $$ is enclosed by a spherical shell of radius $$ r_2 $$ and $$ q_2 $$. charged sphere and shell are connnected by a wire. if $$ q_1 $$ is positive then
  • charge will flow from sphere to shell
  • charge will flow from shell to sphere
  • change flow will depend on magnitude of $$ q_2 $$
  • change flow will depend on magnitude of $$ q_1 $$
Electric charges q, q, -2q are placed at the corners of an equilateral triangle ABC of sideThe magnitude of electric dipole moment of the system is
  • $${ q }^{ 1 }$$
  • $${ 2q }^{ 1 }$$
  • $${ \sqrt { 3 } q }^{ 1 }$$
  • $${ 4q }^{ 1 }$$
Electric field lines in a certain region are shown.
1260345_49c8ca812216440b893036f173f56617.png
  • $${E}_{x}={E}_{y}={E}_{z}$$
  • $${E}_{x}<{E}_{y}<{E}_{z}$$
  • $${E}_{x}>{E}_{y}>{E}_{z}$$
  • $${E}_{x}={E}_{y}<{E}_{z}$$
$$\begin{array} { l } { \text { Three infinitely long charges sheets are placed as shown in figure. The electric field at } } \\ { \text { point } P \text { is } } \end{array}$$
1309324_5a5a3f3021cf42048ccf37aa4411d2b9.jpg
  • $$\frac { 2 \sigma } { \varepsilon _ { 0 } } \hat { k }$$
  • $$- \frac { 2 \sigma } { \varepsilon _ { 0 } } \hat { k }$$
  • $$\frac { 4 \sigma } { \varepsilon _ { 0 } } \hat { k }$$
  • $$- \frac { 4 \sigma } { \varepsilon _ { 0 } } \hat { k }$$
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