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Worksheet on Electric charges and fields

Q1 If a positive charge is displaced against the electric field in which it was situated, then.


a) work will be done by the electric field on the charge.

b) the intensity of the electric field decreases.

c) energy of the system will decrease.

d) energy will be provided by external source displacing the charge.



Q2 If the net electric flux through a closed surface is zero, then we can infer:


a) no net charge is enclosed by the surface.

b) uniform electric field exists within the surface.

c) electric potential varies from point to point inside the surface.

d) charge is present inside the surface.



Q3The SI unit of electric flux is.


a) N to the power (-1) m to the power (-2)

b) NCm to the power (-2)

c) NC to the power (-1) m to the power (2)

d) NC to the power (-1) m to the power (2)



Q4 The electric flux due to a point charge enclosed by a spherical Gaussian surface get affected when its radius is increased:


a) Decreased

b) Increased

c) No change

d) None of these



Q5 The electric flux through a cube of side 1 cm which encloses an electric dipole is :


a) Zero

b) One

c) Two

d) None of these



Q6 If an arbitary surface encloses a dipole, then the electric flux through this surface is.


a) 0

b) 1

c) 2

d) 3



Q7 The force between two small charged spheres having charges of 2 x 10 to the power (-7)C placed 30 cm apart in air is :


a) 4 x 10 to the power (-3 N)

b) 5 x 10 to the power (-3 N)

c) 6 x 10 to the power (-3 N)

d) None of these



Q8 VA and VB are two points on a curved equipotential surface, then relation between VA and VB is :


a) VA < VB

b) VA > VB

c) VA = VB

d) None of these



Q9 Two charges are placed a certain distance apart. A metallic sheet is placed between them. What will happen to the force between the charges ?


a) Increases

b) Decreases

c) Remains unchanged

d) May increase or decrease depending on the nature of metal



Q10The permittivity of vacuum is :


a) 1

b) more than 1

c) less than 1 but not zero

d) zero



Q11 What happens when charge is placed on a soap bubble?


a) It collapses1

b) Its radius increases

c) Its radius decreases

d) None of the above



Q12 Number of electrons in one coulomb of charge will be.


a) 5.46 x 10 to the power (29)

b) 6.25 x 10 to the power (18)

c) 1.6 x 10 to the power (19)

d) 9 x 10 to the power (11)



Q13 Two helium nuclei are separated by a distance 6 nm in vacuum. What is the electrostatic repulsion between them ?


a) 25.6 pN

b) 25. 6 nN

c) 3.6 pN

d) 3.5 pN



Q14 If a charge q is placed at the centre of the line joining two equal like charges Q. The system of three will be in equilibrium if q is.


a) -Q/2

b) -Q/4

c) +Q/2

d) +4Q



Q15 ABC is right angle triangle with AB = 3 cm, BC = 4 cm, AC = 5 cm. Charges 15, 12, - 20 coulomb are placed at A, B, C respectively. The magnitude of the force experienced by the charge at B in newton is.


a) 225 x 10 to the power (13)

b) 125 x 10 to the power (13)

c) 25 x 10 to the power (13)

d) 0



Q16 Which of the following conditions fulfil the condition of having minimum potential energy, if three point charges Q, 2Q and Q are to be placed on a straight line 9 cm long?


a) 2Q and 8Q are placed at ends with Q placed 3 cm from 8Q

b) Q and 8Q are placed at ends with 2Q placed at 6 cm from Q.

c) 2Q and 8Q are placed at ends with Q placed at 6 cm from 8Q.

d) 2Q and Q are placed at ends with Q placed at 3 cm from 2Q.



Q17 If a charge q is placed at the centre of the line joining two equal charges Q such that the system is in equilibrium, then the value of q is.


a) Q /2

b) - Q/2

c) Q/4

d) Q/4



Q18 Two point charges + 9e and + e are 16 cm away from each other. Where should another charge q be placed between them so that the system remains in equilibrium?


a) 24 cm from + 9e

b) 12 cm from + 9e

c) 24 cm from + e

d) 12 cm from + e



Q19 64 small drops of mercury, each of radius r and charge q, coalesce to form a big drop. The ratio of the surface density of charge of each small drop with that of the big drop is.


a) 64 : 1

b) 1 : 64

c) 1 ; 4

d) 4 ;



Q20 Two spherical conductors B and G having equal radii and carrying equal charges on them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of b but uncharged is brought in contact with B, the brought in contact with C and finally removed away from both. The new force of repulsion between B and C is.


a) F/4

b) 3 F / 4

c) F/8

d) 3 F/8



Q21 Which of the following does not allow the electric field lines to cross each other?


a) They originate from positive charge and end at negative charge.

b) They do not pass through the conductor

c) They exhibit longitudinal tension and lateral pressure

d) Superposition of electric fields.



Q22 If an electric dipole is placed in a uniform electric field, it experiences :


a) torque only

b) net force only

c) both torque and net force

d) neither torque nor net force



Q23 Gauss's law helps in :


a) determination of electric force between point charges

b) situations where Coulomb's law fails

c) determination of electric field due to symmetric charge distributions

d) determining electric potential due to symmetric charge distributions



Q24 An electric dipole placed in a non-uniform electric field experiences:


a) both, a torque and a net force

b) only a force but on torque

c) only a torque but on net force

d) no torque and no net force



Q25 Electric field of an isolated hollow metallic. sphere at any interior point is.


a) zero

b) one

c) proportional to field

d) none of these



Q26 An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in a uniform electric field E. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively.


a) q.E and p.E

b) zero and minimum

c) q.E and minimum

d) 2q.E minimum



Q27 An electron enters an electric field with its velocity in the direction of the electric field lines then :-


a) the path of the electron will be circle

b) the path of the electron will be a parabola

c) the velocity of the electron will decrease just after the entry

d) the velocity of the electron will increase just after the entry



Q28 An electron and a proton are set free in a uniform electric field. The ratio of their accelerations is :-


a) unity

b) zero

c) me/mp

d) me/mp



Q29 A charge q is projected into a uniform electric field E; work done when it suffers a displacement Y along the field direction is :-


a) qEY

b) qY/E

c) qE/Y

d) Y/qE



Q30 What will be the ratio of electric field at a point on the axis and an equidistant point on the equatorial line of a dipole :-


a) 1 : 2

b) 2 : 1

c) 4 : 1

d) 1 : 4



Q31 The force on a charge situated on the axis of a dipole is F; if the charge is shifted to double the distance, the force acting will be :-


a) zero

b) F/2

c) F/4

d) F/8



Q32 A charge given to any conductor resides on its outer surface, because :-


a) the free charge tends to be in its minimum potential energy state.

b) the free charge tends to be in its minimum kinetic energy state.

c) the free charge tends to be in its maximum potential energy state.

d) the free charge tends to be in its maximum kinetic energy state.



Q33 For a uniformly charged sphere, the electric field from its centre :-


a) increases linearly up to the surface

b) decreases linearly up to the surface

c) remains zero up to the surface

d) first increases and then decreases up to the surface



Q34 A charge Q is enclosed by a Gaussian spherical surface of radius R. If the radius is doubled, then the outward electric flux will :-


a) increase four times

b) be reduced to half

c) remain the same

d) be doubled



Q35 Identify the incorrect statements for electric charge q :-


a) Quantised

b) Conserved

c) Additive

d) Non-transferable



Q36 An electric dipole is placed in a non uniform electric field, then it experiences :-


a) a force which must be zero

b) a torque which must be non zero

c) a force which must be non zero

d) both a force and a torque which may be non zero



Q37 Assertion :- Electrostatic force between two charges is a conservative force.

Reason :- Electric force between two charges is inversely proportional to the square of distance between the two.


a) A

b) B

c) C

d) D



Q38 Assertion :- On going away from a point charge or a small electric dipole, electric field decreases at the same rate in both cases.

Reason :- Electric field is inversely proportional to the square of distance from the charge or an electric dipole.


a) A

b) B

c) C

d) D



Q39 Assertion :- Electric field lines do not cut at any point.

Reason :- At any point, there is only one direction of electric field.


a) A

b) B

c) C

d) D



Q40 Assertion :- Gauss's law can not be used to calculate electric field near an electric dipole.

Reason :- Electric dipoles do not have symmetrical charge distribution.


a) A

b) B

c) C

d) D



Q41 Assertion :- Electrostatic field lines never form closed loops.

Reason :- Electrostatic field is a conservative field.


a) A

b) B

c) C

d) D



Q42 Assertion :- Electric field inside a metal surface is zero in electrostatic condition.

Reason :- Electric charges exist only on the surface of conductor.


a) A

b) B

c) C

d) D



Q43 Assertion :- Two charged particles at rest experiences only electrical force.

Reason :- Charges at rest can only produce electric field.


a) A

b) B

c) C

d) D



Q44 Assertion :- Electric force is the reason for existence of molecules.

Reason :- At atomic level electric force is the most effective force or strongest force.


a) A

b) B

c) C

d) D



Q45 In Nature the electric charge of any system is always equal to.


a) half integral multiple of the least amount of charge

b) zero

c) square of the least amount of charge

d) integral multiple of the least amount of charge



Q46 Consider a neutral conducting sphere. A positive point charge is placed outside the sphere. The net charge on the sphere is then.


a) negative and distributed uniformly over its surface

b) negative and appears only at the point on the sphere closest to the point charge

c) negative and distributed non-uniformly over its surface

d) zero



Q47 Force between two identical spheres charged with same charge is F. If 50% charge on one sphere is transferred to the other sphere then new force will be.


a) 3F/4

b) 3F/8

c) 3F/2

d) none of these



Q48 A point charge q1 exert a force F, upon another charge q2 . If a third charge q3 be placed quite close to charge q2 then the force that charge q1 exerts on the charge q2 will be :-


a) F

b) >F

c) <F

d) zero



Q49 The force of repulsion between two point charges is F, when these are 1m apart. Now the point charges are replaced by conducting spheresof radii 5 cm having the charge same as that of point charges. The distance between their centres is 1m, then the force of repulsion will be.


a) increase

b) decrease

c) remain same

d) become twice



Q50 Two charges 4q and q are placed at distance x apart. A third charge Q is placed in the middle. If resultant force on q is zerothe Q =


a) q

b) -q

c) 2q

d) -2q



Q51 Two similar spheres having +q and -q charges are kept at certain separation. F force acts between them. If another similar sphere having +q charge is kept in the middle, it experiences a force in magnitude and direction.


a) zero having no direction

b) 8F towards +q charge

c) 8F towards -q charge

d) 4F towards +q charge



Q52 Identify the wrong statement in the following: Coulomb's Law correctly describes the electric force that.


a) binds the electrons of an atom to its nucleus

b) binds the protons and neutrons in the nucleus of an atom

c) binds the atoms together to form molecules

d) binds the atoms and molecules together to form solids



Q53 Choose the correct statement regarding electric field lines.


a) they emerge from negative and terminate at positive

b) the electric field in that region is weak where the density of electric field lines are more

c) they are in radial directions for a point charge

d) they have a physical existence



Q54 Two-point charges + 9q and +q are kept 16 cm apart. where should a third charge Q be placed between them so that the system remains in equilibrium?


a) 24 cm from + 9q

b) 12 cm from + 9q

c) 24 cm from + q

d) 12 cm from + q



Q55 Two equal and like charges when placed 5 cm apart experience a repulsive force of 0.144 newtons. The magnitude of the charge in micro-coulomb will be.


a) 0.2

b) 2

c) 20

d) 12



Q56 Three-point charges are placed at the corners of an equilateral triangle. Assuming only electrostatic forces to be acting :-


a) if the charges have different magnitudes and different signs, the system will be in equilibrium.

b) the system will be in equilibrium if the changes have the same magnitude but different signs.

c) the system can never be in equilibrium.

d) the system will be in equilibrium if the charges rotate about the centre of the triangle.






ANSWERS


1) d

2) a

3) d

4) c

5) a

6) a

7) c

8) c

9) b

10) c

11) b

12) b

13) a

14) b

15) a

16) d

17) d

18) b

19) c

20) d

21) d

22) a

23) c

24) a

25) a

26) b

27) c

28) c

29) a

30) b

31) d

32) a

33) a

34) c

35) d

36) d

37) b

38) d

39) a

40) a

41) a

42) b

43) d

44) a

45) d

46) d

47) a

48) a

49) b

50) b

51) c

52) b

53) c

54) b

55) a

56) c

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