NCERT Solutions for class 12 Physics | Chapter 4 - Moving Charges and Magnetism

(1) Tesla is a unit of:
[A] electric flux
[B] magnetic flux
[C] magnetic field
[D] electric field
Answer: magnetic field
(2) A cyclotron can be used to produce high energy:
[A] neutrons
[B] deutrons
[C] β particles
[D] α partifcles
Answer: α partifcles

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(3) Two identical bar magnets each of dipole moment p and length I are perpendicular to each other as shown in Fig. The dipole moment of the combination is:

[A] √2 p
[B] p/√2
[C] P
[D] 2p
Answer: √2 p
(4) An electron having mass ‘m’ and Kinetic energy E enters in uniform magnetic field B perpendicular, then its frequency will be:
[A] eE/qmB
[B] 2πm/eB
[C] eB/2πm
[D] 2m/eBE
Answer: eB/2πm
(5) The torque acting on a magnetic dipole of moment when placed in a magnetic field
[A] pmB
[B]
[C]
[D]
Answer:
(6) A charge q moves in a region, where electric field E and magnetic field B both exist, then force on it is :
[A]
[B]
[C]
[D]
Answer:
(7) A charged particle of mass m and charge q travels on a circular path of radius r i.e., perpendicular to the magnetic field B. The time taken by particle to complete on revolution is :
[A] 2πqB/m
[B] 2πm/qB
[C] 2πmq/B
[D] 2πq2B/m
Answer: 2πm/qB
(8) The permeability of a paramagnetic substance is:
[A] very large
[B] small but more than unity
[C] less than unity
[D] negative
Answer: small but more than unity
(9) A current carring coil is placed in a uniform magnetic field. If the coil turns through an angle θ, then the torque is directly proportional to:
[A] sin θ
[B] cos θ
[C] cot θ
[D] tan θ
Answer: cos θ
(10) The current sensitibility of a moving coil galanometer increases with decrease in:
[A] magnetic field
[B] area of a coil
[C] number of turns
[D] None of these
Answer: None of these
(11) In thomson spectrograph then velocity of electron beam will be:
[A]
[B]
[C]
[D] E² / B²
Answer:
(12) The force experienced by a particle of charge q moving with velocity in a magnetic field is given by,
[A]
[B]
[C]
[D]
Answer:
(13) According to Ampere’s Circuital law
[A]
[B]
[C]
[D]
Answer: B
(14) A positive charge enters in a magnetic field and travels parallel to but opposite the field. If experiences
[A] an upward force.
[B] a downward force.
[C] an accelerated force.
[D] no force.
Answer: an accelerated force.
(15) An electron is projected along the axis of a circular conductor carrying the same current. Electron will experience
[A] a force along the axis.
[B] a force perpendicular to the axis.
[C] a force at an angle of 4° with axis.
[D] no force experienced.
Answer: no force experienced.
(16) The gyro-magnetic ratio of an electron in an H-atom, according to Bohr model, is
[A] independent of which orbit it is in.
[B] neutral
[C] positive
[D] increases with the quantum number n.
Answer: independent of which orbit it is in.
(17) A conducting circular loop of radius r carries a constant current i. It is placed in a uniform magnetic field B, such that B is perpendicular to the plane of the loop. The magnetic force acting on the loop is
[A] irB.
[B] 2πriB
[C] zero
[D] πriB
Answer: zero
(18) If the beams of electrons and protons move parallel to each other in the same direction, then they
[A] attract each other.
[B] repel each other.
[C] no relation.
[D] neither attract nor repel.
Answer: repel each other.
(19) A current loop placed in a non-uniform magnetic field experiences
[A] a force of repulsion.
[B] a force of attraction.
[C] a torque but not force.
[D] a force and a torque.
Answer: a force and a torque.
(20) The maximum current that can be measured by a galvanometer of resistance 40 Ω is 10 mA. It is converted into voltmeter that can read upto 50 V. The resistance to be connected in the series with the galvanometer is
[A] 2010 Ω
[B] 4050 Ω
[C] 5040 Ω
[D] 4960 Ω
Answer: 4960 Ω

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