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NCERT Solutions for class 12 Physics | Chapter 1 - Electric Charges and Fields

(1) The unit of electric dipole moment is
[A] newton
[B] coulomb
[C] farad
[D] debye
Answer: debye
(2) The force per unit charge is known as
[A] electric flux
[B] electric field
[C] electric potential
[D] electric current
Answer: electric field

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(3) The surface considered for Gauss’s law is called
[A] Closed surface
[B] Spherical surface
[C] Gaussian surface
[D] Plane surface
Answer: Gaussian surface
(4) Consider a region inside which, there are various types of charges but the total charge is zero. At points outside the region
[A] the electric field is necessarily zero.
[B] the electric field is due to the dipole moment of the charge distribution only.
[C] the dominant electric field is inversely pro-portional to r3, for large r (distance from ori-gin).
[D] the work done to move a charged particle along a closed path, away from the region will not be zero.
Answer: the dominant electric field is inversely pro-portional to r3, for large r (distance from ori-gin).
(5) The SI unit of electric flux is
[A] N C-1 m-2
[B] N C m-2
[C] N C-2 m2
[D] N C-1 m2
Answer: N C-1 m2
(6) Which of the following statements is not true about Gauss’s law?
[A] Gauss’s law is true for any closed surface.
[B] The term q on the right side side of Gauss’s law includes the sum of all charges enclosed by the surface.
[C] Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.
[D] Gauss’s law is based on the inverse square dependence on distance contained in the coulomb’s law
Answer: Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.
(7) Electric field lines provide information about
[A] field strength
[B] direction
[C] nature of charge
[D] all of these
Answer: all of these
(8) SI unit of permittivity of free space is
[A] Farad
[B] Weber
[C] C2N-1 m-2
[D] C2N-1 m-2
Answer: C2N-1 m-2
(9) Which of the following figures represent the electric field lines due to a single negative charge?
[A]
[B]
[C]
[D]
Answer:
(10) A charge Q is placed at the centre of the line joining two point charges +q and +q as shown in the figure. The ratio of charges Q and q is

[A] 4
[B] 1/4
[C] -4
[D] -1/4
Answer: -1/4
(11) The minimum amount of charge observed so far is:
[A] 1 C
[B] 4.8 × 1-13 C
[C] 1.6 × 10-19 C
[D] 1.6 × 1019 C
Answer: 1.6 × 10-19 C
(12) The unit of intensity of electric field is :
[A] metre/volt
[B] Joule/newton
[C] Coulomb/newton
[D] Newton/coulomb
Answer: metre/volt
(13) Quantisation of charge implies:
[A] Charge does not exist
[B] Charge exists on particles
[C] There is a minimum permissible magnitude of charge
[D] Charge can’t be created
Answer: There is a minimum permissible magnitude of charge
(14) In non-uniform electric field, electric dipole experiences:
[A] torque only
[B] torque as well as net force
[C] force only
[D] None of these
Answer: torque as well as net force
(15) The SI units of electric dipole moment are:
[A] C
[B] Cm-1
[C] Cm
[D] Nm-1
Answer: Cm
(16) When placed in a uniform field, a dipole experiences:
[A] a net force
[B] a torque
[C] both a net force and torque
[D] neither a net force nor a torque
Answer: a torque
(17) The dielectric constant of a metal is:
[A] 0
[B] 1
[C] ∞
[D] -1
Answer: ∞
(18) A soap bubble is given a negative charge, then its radius:
[A] increases
[B] decreases
[C] remains unchanged
[D] may increase or decrease
Answer: increases
(19) A parrot comes and sits on a bare high power line. It will:
[A] experience a mild shock ‘
[B] experience a strong shock.
[C] get killed instantaneously
[D] not be affected practically
Answer: not be affected practically
(20) An electron is sent in an electric field of magnitude 9.1 × 106NC-1. The acceleration produced in it is :
[A] 1.6 ms-2
[B] 1.6 × 1018ms-2
[C] 3.2 × 1018ms-2
[D] 0.8 × 1018 ms-2
Answer: 1.6 × 1018ms-2

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