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

Two charges +20μC and 20μC 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
  • 8.6×109NC1
  • 4.1×106NC1
  • 3.6×106NC1
  • 4.6×105NC1
Which of the following statements about dipole moment is not true ?
  • The dimension of dipole moment is [LTA]
  • 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 24NC1 and the electric potential at point is 12JC1. The order of magnitude of charge q is
  • 106C
  • 107C
  • 1010C
  • 109C
Choose the correct answer from the alternatives given.
If ε0 and μ0 are respectively the electric permittivity and the magnetic permeability of free space and ε and μ the corresponding quantities in a medium, the refractive index of the medium is
  • μεμ0ε0
  • μεμ0ε0
  • μ0ε0με
  • μμ0εε0
The electric field and the  potential of an electric dipole vary with distance r as
  • 1r and 1r2
  • 1r2 and 1r
  • 1r2 and 1r3
  • 1r3 and 1r2
Figure shows electric field lines in which an electric dipole 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 1r.
  • For a dipole, the potential depends on the magnitude of position vector and dipole moment vector.
  • The electric dipole potential varies as 1r at large distance.
  • For a point charge, the electrostatic field varies as 1r2.
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 K1 times
Choose the correct statement
  • Polar molecules have permanent electric dipole moment
  • CO2 molecule is a polar molecule
  • H2O is a non-polar molecule
  • The dipole field at large distances falls of as 1r2
Which among the following is an example of polar molecule?
  • O2
  • H2
  • N2
  • 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 27×1022Cm2. The electric field   E in region II in between the plates is
941270_2a11cb97bb5f48718b234f90bb4a67f7.PNG
  • 4.25×108NC1
  • 6.28×1010NC1
  • 3.05×1010NC1
  • 5.03×1010NC1
Two conducting and concentric thin spherical shells or radii a and b,(b>a) have charges q1 and q2 respectively. Now if the inner shell is earthed then the final charge on this shell will be
  • q2a2b2
  • q2ab
  • (q1+q2)2
  • q2ba
A uniform line charge with linear density λ lies along the y-axis. What flux crosses a spherical surface centred at he origin with r = R
  • 2Rλϵ0
  • Rλϵ0
  • λϵ0
  • none of the above
The electric field of a radio wave is given by E=Esin(Kzωt)(ˆi+ˆj) . Give a unit vector
in the direction of the magnetic field at a place and time where sin(kzωt) is positive.
  • (ˆi+ˆk)/2
  • (ˆiˆk/2
  • ˆi+ˆj/2
  • ˆiˆj/2
Two concentric spherical shells of radii R and 2R 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 xaxis. 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 xaxis, is approximately proportional to:
  • x
  • x2
  • x3
  • 1x
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 with the direction of electric field. Find the flux of the electric field  through the rectangular surface 
  • 0.1675  Nm2/C
  • 0.1875  Nm2/C
  • Zero
  • 0.1075  Nm2/C
Consider an electric field ˉE=E0ˆx where E0 is a constant. The flux through the shaded area (as shown in the figure) due to this field is
1010537_3586de4a6fd8414cbc48e9028b80b378.png
  • 2E0a2
  • 2E0a2
  • E0 a2
  • E0a22
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/22/3
  • y=x/21/3

Three charge +4q, Q and q are placed in a straight line of length l at points distance 0, l2 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  (K=14πεo)


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 EA,EB and EC 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 

  • EAEB
  • EAEB
  • |EB|4|EC|
  • |EB|8|EC|
A point charge is placed at the corner of a cube. The electric flux through the shaded surface is 
1019651_e34ec158f02c4fa2b3e4110f066ed20f.png
  • q8ε0
  • qε0
  • q24ε0
  • q12ε0
A charge Q is divided into two parts of q and Qq. If the Coulomb repulsion between them when they are separated, is to be maximum, the ratio of Qq 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
  • r2
  • r2
  • 2r
  • r
The total electric flux through a cube when a charge 8q is placed at one corner of the cube is
  • ε0q
  • ε0q
  • 4πε0q
  • qε0
A square of side 'a' is lying in xy plane that two of its sides are lying on the axis. If E=E0xˆk is applied on the square. The flux passing through the square is
  • E0a2
  • E0a32
  • E0a33
  • E0a22
The ratio of the electric force between two proton to that between two electrons under similar conditions is the order of:
  • 1042
  • 1039
  • 1036
  • 1
A point charge +q is placed at the centre of a cube of side L. The electric flux emerging from the cube is
  • qε0
  • zero
  • 6qL2ε0
  • q6L2ε0

The chasrge density of an insulating infinity surface is (e/π)cm2 then the field intensity at a nearby point in volt/meter will be -

  • 2.88×1012
  • 2.88×1010
  • 2.88×109
  • 2.88×1018
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 1/4πϵ0 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 qQ2πε0+(qQ2πε0)2+4m2u2a22mu2
  • 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 P slowly in uniform electric field of intensity E from 00 to 1800
  • 2 PE
  • 8 PE
  • 9 PE
  • 5 PE
A charged oil drop od mass 2.5×107kg is in space between the two plates, each of area 2×102m2 of a parallel plate capacitor. When the upper plate has a charge of 5×107C and the lower plate has an equal negative charge then the oil remains stationery. The charge of the oil drop is (take, g=10m/s2)
  • 9×101C
  • 9×106C
  • 8.85×1013C
  • 1.8×1014C
What is the angle between the electric dipole moment and the electric field strength due to it on the equatorial line?
  • 0o
  • 90o
  • 180o
  • 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 _____
  • 14π2toQr
  • Q2πε0r
  • Zero
  • 2πQr
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/ϵo
  • 2q/ϵo
  • q/ϵo
  • 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 λ in a circular path of radius r. Its kinetic energy is given by:
  • λe8πϵ0r
  • λe4πϵ0r
  • λe2πϵ0r
  • λe4πϵ0
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 cm2 is placed in a uniform electric field of 20 N/C such that the angle between the surface and the electric field is 30o. The electric flux over the surface is:
  • 0.0173 Vm
  • 0.0236 Vm
  • 0.01 Vm
  • 0.0346 Vm
A point charge of value 107 C is situated at the centre of cube of 1 m side. The electric flux through its total surface area is:
  • 113×104 Nm2/C
  • 11.3×104 Nm2/C
  • 1.13×104 Nm2/C
  • none of these
A  wire of linear charge density λ passes through a cuboid of length , breadth b and height h (>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 :
  • l2+b2h
  • l2+b2+h2h
  • hl2+b2
  • ll2+b2+h2
A point charge of +6μC 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
  • ϵ0
  • 1ϵ0
  • ϵ0×106
  • 1ϵ0×106
If the dipole is place in a non-uniform electric field an angle θ, in addition tarque 
  • Experiences a force
  • Experiences a repulsive force
  • No any kind of force
  • Neither attractive nor repulsive force
There are two charges +2μ C and3μ 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?
  • q2 and q2
  • q4 and 3q4
  • q3 and 2q3
  • q5 and 4q5
0:0:2


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