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Electrostatics â?– Illustrative Examples 1) The distance between electron and proton in the H-atom is about 5.3 Ă— 10-11 metre. What is the magnitude of electric force between these two particles?
Data :
(Ans. : 2) The two charges of magnitude 1
C and 2
)
C are separated by 10cm from each
other. At what point on the line joining the two charges is the electric field strength zero ? Data :
(Ans. : Solving
)
3) Find the magnitude of an isolated positive point charge, if the electric potential at 10
cm from the charge to be 100V. Data : r = 10cm = 0.1m ,V = 100V, q = ?
(Ans. :
)
4) What is the energy gained by an electron when it is accelerated through a potential difference of 200 V ? Data : 5) Three point charges
(Ans. : and
)
are placed in air at the three
corners of an equilateral triangle having each side of 1.0
m.
Find the resultant force acting on the charge Data :
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(Ans. :
)
6) An electric dipole consist of two opposite charges each of magnitude
separated
try distance 2.0 cm. The dipole is placed in an external uniform field of What maximum torque does the field exert on the dipole ? Data : (for maximum torque) (Ans. :
)
7) Two protons in a nucleus of U238 are 6.0 Ă— 10-15 meter apart.
What is their mutual electric potential energy ? Data :
(charge on proton)
, (Ans. :
)
8) Three charges are arranged as shown in figure. What is the potential energy of the system of charges? Assume that
and
Data :
(Ans. :
)
9) An electric dipole of length 2.0 cm is placed with its axis making an angle of 300 to a uniform electric field of 105 N/C. If it experiences a torque of
Nm. Calculate (a)
the magnitude of charge on the dipole and (b) potential energy of the dipole. Data :
(Ans. : 10) Three point charges + q, + 2q and Q are placed at the three vertices of an equilateral triangle. Find the value of charge Q (in terms of q), so that electric potential energy of the system is zero.
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)
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Data :
(Ans. :
)
â?– Theory Questions 1) State Coulomb's law and express it in vector form. 2) Define the intensity of electric field at a point. 3) Obtain an expression for the intensity of an electric field at a point due to point charge. 4) Explain, what is meant by dielectric constant of medium? 5) What is the principle of superposition of forces ? 6) Establish the relation between electric field intensity & electrostatic force. 7) Define electric potential. Derive an expression for electric potential at a point due to point charge. 8) Define electric potential gradient. Obtain the relation between electric field intensity and potential gradient at a point in the electric field. 9) What is electron-volt ? 10) What is meant by an electric dipole? Define electric dipole moment and state its SI unit. 11) What are electric lines of force ? State the properties of lines of force. 12) What is meant by the term electric potential difference ? 13) Derive an expression for electric potential due to an electric dipole. 14) What do you mean by equipotential surface ? What will be the shapes of equipotential surfaces in case of uniform field and point charges? 15) Derive an expression for the total work done in rotating an electric dipole through an angle
in a uniform electric field.
16) Derive an expression potential energy of a system of two point charges. 17) Derive an expression for the potential energy of an electric dipole in uniform electric field. 18) Obtain an expression for potential energy of the configuration of three charges. 19) Explain what is charge. State different types of charges. Write down its unit and dimension. 20) State the main characteristics of electric charges.
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21) Define frictional electricity. State two examples. 22) Explain frictional electricity in terms of electron transfer. 23) State and explain the principle of conservation of charges with example. 24) A charged metallic sphere A is suspended by a nylon thread. Another charged metallic sphere B held by an insulating handle is brought close to A such that the distance between their centres is 10 cm, as shown in figure (a). The resulting repulsion of A is noted (for example, by shining a beam of light and measuring the deflection of its shadow on a screen.) Spheres A and B are touched by uncharged spheres C and D respectively, as shown in figure (b). C and D are then removed and B is brought closer to A to a distance of 5.0 cm between their centres, as shown in figure (c). What is the expected repulsion of A on the basis of Coulomb’s law? Spheres A and C and spheres B and D have identical sizes. Ignore the sizes of A and B comparison to the separation between their centres. 25) Define one coulomb charge according to Coulomb's law. 26) State the limitations of Coulomb's law. 27) Whether dielectric constant decides the strength of electric field? 28) Obtain an expression for the force between multiple electric charges. 29) Explain the concept of continuous distribution of charge. 30) Define the following terms. i. Uniform charge distribution ii. Non-uniform charge distribution 31) Whether surface charge density depends on the shape of the conductor? Justify. 32) Explain the terms: (a) Linear charge density (b) Surface charge density (c) Volume charge density 33) Define electric field. 34) Define the following terms. i) ii) iii)
Uniform electric field Non-uniform electric field Radial electric field.
35) What will happen if a test charge is kept beyond electric field due to certain charge? 36) i. An electrostatic field line is a continuous curve. That is, a field line cannot have the sudden breaks. Why not? ii. Explain why two field lines never cross each other at any point. 37) With the help of diagram, show the variation of electric lines of force in different electric fields. 38) Which among the below cannot, possibly represent electrostatic field lines?
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39) Define polar substances. 40) Define non-polar substances. 41) Define the following terms. i. Axis of dipole
ii. Equator of dipole
42) Derive an expression for torque acting on a dipole in a uniform electric field. Discuss maximum and minimum value of torque. 43) Define dipole moment. 44) State the expression for magnitude of torque acting on a dipole in a uniform magnetic field and give its physical significance. 45) Define electrostatic potential energy. Electrostatic potential energy. 46) Give a note on electric potential difference. 47) State unit of electric potential at a point. Discuss the factors on which electric potential depends. 48) Distinguish between electric field intensity and electric potential. 49) Obtain an expression for electric potential due to a system of charges. 50) Electric field intensity and electric potential vary with distance of point from charge. Justify. 51) Derive an expression for potential energy of the system of two charges in an electric field. 52) Derive an expression for potential energy of dipole in an external field. 53) Explain the terms. a. Volt
b. Electron volt
54) Explain the term electric flux in an electric field. 55) Define electric flux density. State its SI unit.
â?– Textbook problems 1) Two small spheres are charged positively, the combined charge being
If
each sphere is repelled from the other by a force of 1.0 N when the spheres are 2.0 metre apart, how is the total charge distributed between the spheres ? (Ans :
)
2) What is the magnitude of a point charge chosen so that the electric field 50cm away has magnitude 2.0 N/C?
(Ans :
)
3) How many electrons would have to be removed from a coin to leave it with charge of ?
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(Ans : Electrostatics
)
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4) What is the force experienced by a test charge of
placed in an electric field of
N/C?
(Ans: 0.64N)
5) What is the electric potential at the centre of square of side 1 m? The charges and
are placed at the corners of the square. (Ans : 509V)
6) Find the work done when a point charge of
is moved from a point at a
potential of -10V to a point at which the potential is zero.
(Ans :
)
7) A particle carrying 5 electrons starts from rest and is accelerated through a potential difference of 8900V. Calculate the K.E. acquired by it in MeV. (Charge on electron
)
(Ans : 0.045MeV)
8) An electron is circulating around the nucleus of H-atom in a circular orbit of radius Calculate the electric potential energy of the atom in eV.(Ans : -27.17 eV) 9) Consider a point charge with a) What is the radius of an equipotential surface having a potential of 30 V ? b) Are surfaces whose potential differ by constant amount (say 1.0 V) evenly spaced in radius ?
(Ans : 4.5 m, yes)
10) What is the electric potential energy of the charge configuration (See fig). Assume that
(Ans :
)
11) An electric dipole consists of two opposite charges of magnitude separated by 4.0 cm. The dipole is placed in an external field of 105 N/C. Find the work done by an external agent to turn the dipole through 1800.
(Ans : 0.016 J)
❖ Practice problems ➢ Type-I : Problems based on coulomb’s law
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1) What is the force between two small charge spheres having charges of 2 and 3
10-7 C
10-7 C placed 30 cm apart in air ? (Ans. The forces between the charged spheres is 6
2) The electrostatic force on a small sphere of charge 0.4 sphere of charge -0.8
10-3 N.)
C due to another small
C in air is 0.2 N. (i) What is the distance between the two
spheres? (ii) What is the force on the second sphere due to the first ? (Ans. i. Distance between the two spheres is 12 cm. ii. The force on the second sphere is 0.2 N.) 3) There are three charges of magnitude 3
C, 2
C and 3
C located at three
corners A, B and C of a square ABCD of each side measuring 2 m. Determine the net force on 2
C charge.
(Ans. Net force on q2 is 1.91
4) Calculate the force between two electric charges 5 distance of 10 cm.
and
10-2 N.)
separated by a
(Ans : 9 N, Force of attraction)
5) i. Two insulated charged copper spheres A and B have their centres separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion, if the charge on each is 6.5
10-7 C? The radii of A and B are negligible compared to the distance
of separation. ii. What is the force of repulsion if each sphere is charged double the above amount and the distance between them is halved? (Ans. i. The mutual force of electrostatic repulsion is 1.52
10-2 N,
ii. When charge is doubled and distance is halved, the force of repulsion is 0.24 N.) 6) The force between two charges when separated by a distance of 50 cm in air is 40 newton. What will be the force between them if the distance becomes 25 cm? (Ans : 160 N) 7) Point charges having values
and
are placed at the
comers A, B, C and D respectively of a square of side one metre. Calculate the magnitude of the force on a charge of
placed at the centre of the square. (Ans :
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)
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8) Find the force of attraction between a point charge of
and a point charge of
when they are situated in air at a distance of 30 cm from each other. (Ans : -2 N, attraction)
➢ Type-II : Problems based on charge density 9) Surface charge density of a hollow cylinder is 10 density? (Radius of cylinder = 15 cm) 10) If a charge of 400
C/m2. What is its linear charge
(Ans. Linear charge density is 9.42
C/m. )
C is distributed uniformly over an electric wire of length 2 cm,
surface area 10 cm2 and volume of 2 cm3. Calculate i. The linear density. ii. The surface density. iii. Volume density of charge. (Ans.The linear, surface and volume density of given charge 2
102 C/m2, 0.4 C/m2, 2
configuration is
102 C/m3 respectively.)
11) A metal cube of length 0.1 m is charged by
calculate its
i. linear charge density ii. Surface charge density iii. Volume charge density (Ans : i.
ii.
iii.
12) A uniformly charged sphere carries a total charge of
)
Its radius is 5 cm
and is placed in vacuum. Determine its surface charge density.(Ans : 13) If a charge of 400
)
is distributed uniformly over an electric wire of length 2 cm, a
surface area 10 cm2 and volume of 2 m3. Calculate i. the linear density
iii. volume density of charge respectively for distribution
ii. the surface density
(Ans : i.
ii.
iii.
)
➢ Type-III : Problems based on electric field intensity 14) The force exerted by an electric field on a charge of + 10
C at a point is16
10-4 N.
What is the intensity of the electric field at the point ? (Ans. The electric field intensity at the given point is 160 N/C.)
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15) What is the force experienced by a test charge of 0.20 of 3.2
106 N/C?
(Ans. The force experienced by the test charge is 0.64 N.)
16) Find the distance from a charge of 4 intensity 9
C placed in an electric field
C placed in air which produces electric field of
103 N/C.
(Ans. The distance from the charge is 2 m.)
17) Two point charges qA =3
C and qB = -3
C are located 20 cm apart in vacuum.
a. What is the electric field at the midpoint O of the line AB joining the two charges? b. If a negative test charge of magnitude 1.5
10-9 C is placed at this point, what is
the force experienced by the test charge? (Ans. The electric field at midpoint is 5.4
106 N/C along OB and the force
experienced by the test charge is 8.1
10-3 N along OA.)
18) Calculate the electric field intensity at a point distance 10 metre from a point charge of 2 coulomb in air.
(Ans :
19) Two point charges A and B of 100
and -400
)
are kept 3 cm apart. Find the
point where the electric field due to the two charges vanishes. (Ans : At a point cm away from A on BA produced) 20) Point charges of 10
, -20
, 10
and 40
are situated in air at the comers
A, B, C and D respectively of a square taken in order. If each side is of length 2 m, find the electric intensity at the intersection ‘O’ of the diagonals. (Ans :
)
➢ Type-IV : Problems based on electric potential due to point 21) Consider a point charge with q = 1.5
10-8 C
i. What is the radius of an equipotential surface having a potential of 30 V? ii. Are surfaces whose potential differ by constant amount (say 1.0 V) evenly spaced in radius.
(Ans. i. The radius of the equipotential surface is 4.5 m. ii. Surfaces with constant potential difference are evenly spaced. If they are kept in uniform electric field.)
22) Find the potential midway between two point charges 2
10-9 C and 5 10-9 C, 0.2
m apart. How much work must be done in placing a third charge 4 point.
10-9 C at that
(Ans. i. The potential midway between the two charges is 315 V. ii. Work done in placing a third charge is 2.52
10-6 J.)
23) If 100 joules of work must be done to electric charge equal to 4 C from a place, potential is -10 volt to another place potential is V volt. Find the value of V.
F.Y.J.C. Science
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CONTACT: 9821131002/9029004242 (Ans. The potential at the place is 15 V.)
24) The electric field at a point due to a point charge is 10 N C-1 and the electric potential at that point is 15 J C-1. Calculate the distance of the point from the charge and the magnitude of the charge. 25) A point charge of -0.2
(Ans :
is placed at a point 6 mm from the charge of 0.2
Calculate its dipole moment. 26) Two point charges of +12
) .
(Ans : and -12
)
are situated in air at a distance of 10 cm
from each other. Compute the potential at a point, in between the charges, at a distance of 6 cm from the positive charge.
(Ans :
27) ABCD is a square of side 0.2 m. Charges of
)
are placed
respectively at the corners A, B and C. Find the work required to be done to move an charge of
from D to the centre of the square.
(Ans :
28) Four point charges
and
) are
placed in a medium of dielectric constant 2 at the comers of a square with a side 2m. Find the electric potential at the point of intersection of the diagonals. (Ans : 85.9 V) 29) Calculate the potential at the centre ‘O’ of the square with the charge at the comers as shown in figure. given
(Ans : 636.4 V)
➢ Type-V : Problems based on electric potential energy 30) Two point charges +10
C and -10
C are separated by a distance of 40 cm in air.
Calculate the potential energy of the system. (Ans. The potential energy of the system is -2.25 J.) 31) A system has two charges qA = 2.5
10-7 C and eB = -2.5
10-7 C located at points
A: (0, 0, -15 cm) and B: (0, 0, +15 cm), respectively. What are the total charge and electric dipole moment of the system? ( Ans: i. Total charge of the system is zero. ii. Electric dipole moment of the system is 7.5
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10-8 C m along Z-axis.
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32) An electric dipole has opposite charges of magnitude 2
10-15 C separated by a
distance of 0.2 mm. It is placed in a uniform electric field of 103 N/C. Find the magnitude of dipole moment. (Ans. The magnitude of dipole moment is 4 10-19Cm.) 33) An electric dipole of length 4 cm, when placed with its axis making an angle of 60° with uniform electric field experiences a torque of
N-m. If the dipole has charge
8 × 10-9 C, calculate the potential energy of the dipole.
(Ans :
34) Determine the potential energy of a system containing two charges 7
)
and -2
separated by a distance of 18 cm.
(Ans :
)
➢ Type-VI : Problems based on electric dipole moment 35) A system has two charges qA : 2.5
10-7 C and qB -2.5
10-7 C located at points A:
(0, 0, -15 cm) and B: (0, 0, +15 cm), respectively. What are the total charge and electric dipole moment of the system? (Ans. i. Total charge of the system is zero. ii. Electric dipole moment of the system is 7.5
10-8 C m along Z-axis.)
36) An electric dipole has opposite charges of magnitude 2
10-15 C separated by a
distance of 0.2 mm. It is placed in a uniform electric field of 103 N/C. Find the magnitude of dipole moment.
(Ans :
)
➢ Type-VII : Miscellaneous 37) Coulomb’s law for electrostatic force between two point charges and Newton’s law for gravitational force between two stationary point masses, both have inverse-square dependence on the distance between the charges/masses. (a) Compare the strength of these forces by determining the ratio of their magnitudes for an electron and a proton, (b) Estimate the accelerations of electron and proton due to the electrical force of their mutual attraction when they are
(Ans : (a)
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apart.
(b)
and
)
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38) An electric dipole with dipole moment of a uniform electric field of magnitude
C m is aligned at 30° with the direction Calculate the magnitude of
torque acting on the dipole.
(Ans : 10-4 N m.)
39) The electric field at a point due to a point charge is 20 N C-1 and the electric potential at that point is 10 J C-1. Calculate the distance of the point from the charge and the magnitude of the charge.
(Ans : (i) 0.5m, (ii)
)
40) Three charges each of magnitude 1 C are located at the three corners of an equilateral triangle of side 1 m as shown in the figure. Find the electric intensity at the C.G. of triangle.
(Ans : zero)
41) An electron initially at rest, is accelerated through a potential difference of 300 V. Find the energy acquired by the electron in eV and J. Also calculate the velocity of the electron. [Given: Charge on electron
Mass of electron
(Ans : i. 300 eV or 42) Two identical positive charges each of
]
ii.
)
are 60 cm apart in vacuum. Find
the intensity and potential at the midpoint between them. Also calculate the force acting on each charge.
(Ans : zero and 300 V. ii.
)
43) The electric flux through a plane surface of area 200 cm2 in a region of uniform electric field 20 N/C is 0.2 Nm2/C. Find the angle between electric field and normal to the surface.
(Ans : 60°.)
44) Calculate the potential at a point P due to a charge of 4 × 10-7 C located 9 cm away. Hence obtain the work done in bringing a charge of 2 × 10-9 C from infinity to the point P. 45) Two point charges of +10 p
(Ans : and 20
)
are placed in free space 2 cm apart. Find
the electric potential at the middle point of the line joining the two charges. (Ans : 27 MV) 46) Two charges 2 × 10-6 C and -3 × 10-6 C are placed 0.25 m apart. At what point on the line joining two charges is the electric potential zero?
(Ans : 0.1 m)
47) An electron is accelerated from rest by a P.D. of 1000 volt. Find the energy acquired by the electron in eV and joule. Also find the velocity of the electron. [Mass of electron = 9.1 × 10-31 kg.]
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(Ans :
)
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48) The dipole moment of water molecule in its vapour state is 6.1 × 10-30 C m. If a water molecule is placed in an electric field of 104 N/C, Calculate the maximum torque the field can exert on the molecule. 49) Charges of +10
and -10
(Ans :
)
are placed at the comers Q and R of an equilateral
triangle PQR, each side of which is of length 0.3 m. Find the magnitude of the intensity at P. Find also potential at P.
(Ans : 106 N/C, zero)
50) An electric dipole consists of two opposite charges each of 1
separated by 2 cm.
The dipole is placed in an external uniform field of 105 NC-1 intensity. Find the work done in rotating the dipole through 180° starting from the position
. (Ans : 0.004 J)
51) If 400 joules of work must be done to move electric charge equal to 4 C from a place, where potential is -10 volt to another place, where potential is V volt, find the value of V.
(Ans : 90 V)
52) Determine the magnitude of uniform electric field which is in vertical direction such that a proton placed in this field would experiences an electrostatic force equal to its weight. [Given: mass of proton = 1.67 × 10-27 m kg, g = 9.8 m/s2, charge on proton = 1.6 × 10-19 C]
(Ans : 1.02 × 10-7 N/C or V/m)
53) Two point charges 2 × 10-8 C and -1.5 × 10-8 C are 50 cm apart in air. ‘A’ is centre of line joining them and ‘B’ is a point at a distance of 30 cm from negative charge. Find potential difference between the points A and B.
(Ans : 2.7 × 102 volt)
54) Three equal charges, each of magnitude q are situated at the comers of an equilateral triangle in air. What is the resultant force on a charge -q at the centroid of the triangle?
(Ans : zero)
55) Calculate the kinetic energy acquired by a point charge of 6.4 × 10-19 C in electronvolt when accelerated by a potential difference of 1000 V.
(Ans : 4000 eV)
56) An electric dipole consists of equal and opposite charges, each of magnitude 8 separated by a distance of 0.2 mm. It is placed in a uniform electric field of intensity 50 N/C with the axis of the dipole inclined to the field 30°. Find i. the electric dipole moment ii. the moment of the couple acting on the dipole (Ans : i. 1.6 × 10-9 C m ii. 4 × 10-8 Nm)
❖ Multiple Choice Questions F.Y.J.C. Science
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INFOMATICA ACADEMY 1) Two point charges +4 of -4
CONTACT: 9821131002/9029004242 and +2
repel each other with a force of 8 N. If a charge
is added to each of these charges, the force would be
(A) zero
(B) 8 N
(C) 4 N
(D) 12 N
2) Force between two charges separated by a certain distance in air is F. If each charge is doubled and the distance between them is also doubled, force would be (A) F
(B) 2F
(C) 4 F
(D) F/4
3) A work of 100 joule is performed in carrying a charge of -5 coulomb from infinity to a particular point in an electrostatic field. The potential of this point is (A) 100 V
(B) 5 V
(C) -20 V
(D) 20 V
4) The unit of electric dipole moment is (A) C - m
(B) C - m2
(C) C2- m
(D) C2 - m2
5) The energy acquired by a charge of 8 × 10-19 C when passed through a potential difference of 200 volt is (A) 500 eV
(B)1000 eV
(C) 1500 eV
(D) 2000 eV
6) For what order of distance is Coulomb’s law true? (A) For all distances. (B) Distances greater than 10~13 m. (C) Distances less than 10~13 m. (D) Distance equal to 10~13 m. 7) In S.I. system, the value of
is
(A)
(C)
(B)
(D)
8) A charge of 10 e.s.u. is placed at a distance of 2 cm from a charge of 40 e.s.u. and 4 cm from another charge of 20 e.s.u. The potential energy of 10 e.s.u., in ergs, is (A) 150
(B) 87.5
(C) 112.5
(D) 25
9) The permittivity of medium is 26.55 × 10-12 C2/Nm2. The dielectric constant of the medium will be (A) 2
(B) 3
(C) 4
(D) 5
10) The electric field intensity at a point 2 m from an isolated point charge is 500 N/C. The electric potential at the point is (A) 0 V
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(B) 2.5 V
(C) 250 V
(D) 1000 V
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11) A force of 2.25 N acts on a charge of 15 × 10-4 C. Calculate the intensity of electric field at that point (A) 1500 NC-1
(B)150 NC-1
(C) 15000 NC-1
(D) 2500 NC-
12) A point charge q produces an electric field of magnitude 2 N C-1 at a point distant 0.25 m from it. What is the value of charge? (A) 1.39 × 10-11 C
(B) 1.39 × 1011 C
(C)13.9 × 10-11 C
(D)13.9 × 1011 C
13) The dimensional formula of electric field intensity is (A) [M1L1T-2A-1]
(B)[M1L1T-3A-1]
(C) [M1L2T-3A-1]
(D) [M1L2T-3A-2]
14) Four coulomb charge is uniformly distributed on 2 km long wire. Its linear charge density is (A) 2 C/m
(B) 4 C/m
(C) 4 × 10-3 C/m (D) 2 × 10-3 C/m
15) A point P is at a certain distance from a point charge q. At P, there is an electric field of intensity 3 V/m and a potential of 24 V. Then the distance of P from the point charge is (A) 6 m
(B) 8 m
(C) 12 m
16) The work done to displace the charge of 5
(D) 10 m
on equipotential surface of potential
5 volt is (A) zero
(B) 2.5 × 10-5 J
(C) 25 × 10-5 J
(D) infinity
17) A 10 C of charge is moved by 0.1 m on an equipotential surface. The work done in doing so is (A) 10 J
(B) 1 J
(C) 0.1 J
(D) zero
18) A system of two charges has positive potential energy. This signifies that ________. (A) both charges are positive (B) both charges are negative (C) both charges are positive or both are negative (D) one charge is positive and the other is negative 19) A spherical surface of radius 20 cm is centered on a point charge and is at a potential 20 V. A charge of 50 nC is moved on the surface between two diametrically opposite points. The work done is (A) l0-7 J
(B) 2.5 × 10-9 J
(C) zero
(D) 3.5 × 10-9 J
20) Potential gradient is a ________. (A) vector quantity
(C) conversion factor
(B) scalar quantity
(D) constant
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21) The electric intensity in air at a point 20 cm from a point charge Q coulombs is 4.5 × 105 N/C. The magnitude of Q is (A) 20
(B) 200
(C) 10
(D) 2
22) An electron whose velocity is 107 m/s has an energy of (A) 4.6 × 10-17 eV
(C) 284 eV
(B) 160 eV
(D) 568 eV
23) In a uniform electric field, a charge of 3 C experiences a force of 3000 N. The potential difference between two points 1 cm apart along the electric lines of force will be (A) 10 V
(B) 3 V
24) Two point charges,
magnitudes of the force, (A) 8 : 1
(C) 0.1 V and
(D) 20 V are a distance r apart. The ratio of the
is
(B) 2 : 1
(C) 1 : 1
(D) 1 : 2
25) A glass rod when rubbed with a piece of fur acquires a charge of magnitude 3.2 . The number of electrons transferred is (A) 2 × 10-13 from fur to glass
(C) 2 × 1013 from glass to fur
(B) 5 × 1012 from glass to fur
(D) 5 × 1012 from fur to glass
26) Work done in moving charge (q) between two points separated by distance
on
an equipotential surface is (A) Zero 27) A charge of 5
(B)
(C)
(D) infinite
is placed at a point. What is the work required to carry 1 C of
charge once round it in a circle of 12 cm radius? (A) 6 × 10-7 J
(B) 60 J
(C) 2.4 J
(D) zero
28) The direction of electric field with respect to the equipotential surface is (A) both have same direction. (B) electric field is perpendicular to the equipotential surface. (C) both have opposite direction. (D) electric field will make an angle of 45° with equipotential surface. 29) A body can be negatively charged by _______. (A) giving excess of electrons to it (B) removing some electrons from it
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(C) giving some protons to it (D) removing some neutrons from it 30) Electric potential of earth is taken to be zero because earth is a good _______. (A) insulator
(C) semi-conductor
(B) conductor
(D) dielectric
31) Which of the following is NOT the property of equipotential surfaces? (A) They do not intersect each other. (B) They are concentric spheres for uniform electric field. (C) Potential at all points on the surface has constant value. (D) Separation of equipotential surfaces increases with decrease in electric field. 32) A charge q is placed at the centre of the line joining two equal positive charges Q. The system of three charges will be in equilibrium (A)
(B)
(C)
(D)
33) Choose the correct answer. (A) Total charge present in the universe is constant. (B) Total positive charge present in the universe is constant. (C) Total negative charge present in the universe is constant. (D) Total number of charged particles present in the universe is constant. 34) A stationary charge produces _______. (A) an electric field only
(C) both electric and magnetic fields
(B) a magnetic field only
(D) an electromagnetic wave
35) An electric dipole of moment p is placed in the position of stable equilibrium in a uniform electric field of intensity E. The torque required to rotate, when the dipole makes an angle 0 with the initial position is (A) pE
(B) pE
(C) pE
(D) pE
36) If a charge is moved against the Coulomb force of an electric field, ________. (A) work is done by the electric field (B) energy is used from some outside source (C) the strength of the field is decreased (D) the energy of the system is decreased 37) The force experienced by a test charge of 2
placed in an electric field of 5.2 ×
106 N/C is (A) 10.4 × 1012 N
(C) 10.4 × 106 N
(B) 10.4 × 109 N
(D) 10.4 N
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38) The force exerted by an electric field on a charge of +10
at a point is 16 × 10-4
N. The intensity of electric field at that point is (A) 16 × 1013 N/C
(C) 16 × 10-9 N/C
(B) 16 × 10-5 N/C
(D) 1.6 × 102 N/C
39) The charge on the electron is 1.6 × 10-19 C. The number of electrons need to be removed from a metal sphere of 0.05 m radius so as to acquire a charge of 4 × 10-15 C is (A) 1.25 × 104
(C) 2.5 × 103
(B) 1.25 × 103
(D) 2.5 × 104
❖ Answer to Multiple Choice Question 1. (A)
2. (A)
3. (C)
4. (A)
5. (B)
6. (B)
7. (D)
8. (D)
9. (B)
10. (D)
11. (A)
12. (A)
13. (B)
14. (D)
15. (B)
16. (A)
17. (D)
18. (C)
19. (C)
20. (A)
21. (D)
22. (C)
23. (A)
24. (C)
25. (A)
26. (A)
27. (D)
28. (B)
29. (A)
30. (B)
31. (B)
32. (B)
33. (A)
34. (A)
35. (B)
36. (B)
37. (D)
38. (D)
39. (D)
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