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91.
A galvanometer having a resistance of 9 ohm is shunted by a wire of resistance 2 ohm. If the total current is 1 amp, the part of it passing through the shunt will be
(1)0.2 amp
(2)0.8 amp
(3)0.25 amp
(4)0.5 amp
92.
If there is no torsion in the suspension thread, then the time period of a magnet executing SHM is
(1)T=2π1MBI
(2)T=2πIMB
(3)T=2π1IMB
(4)T=2πMBI
93.
The radius of the path of an electron moving at a speed of 3.2×107ms−1 in a magnetic field of 6×10−4T perpendicular to it is (mass of electron is 9×10−31kg and charge of electron is 1.6×10−19C )
(1)22.4cm
(2)13cm
(3)30cm
(4)39cm
94.
A moving coil galvanometer has a coil with 175 turns and area 1cm2. It uses a torsion band of torsion constant 10−6N−m/rad The coil is placed in a magnetic field B parallel to its plane. The coil deflects by 1∘ for a current of 1mA. The value of B (in Tesla) is approximately:
(1)10−4
(2)10−2
(3)10−1
(4)10−3
95.
A thin rod of length L has magnetic moment M when magnetised. If rod is bent in a semicirculat arc what is magnetic moment in new shape?
(1)LM
(2)πM
(3)2πM
(4)π2M
96.
The magnetic moments associated with two closely wound circular coils A and B of radius rA = 10 cm and rB = 20 cm respectively are equal if: (Where NA, IA and NB, IB are number of turn and current of A and B respectively)
(1)2NAIA = NBIB
(2)NA = 2NB
(3)NAIA = 4NBIB
(4)4NAIA = NBIB
97.
Consider a circular coil of wire carrying constant current I, forming a magnetic dipole. The magnetic flux through an infinite plane that contains the circular coil and excluding the circular coil area is given by φi. The magnetic flux through the area of the circular coil area is given by φo Which of the following option is correct?
(1)φi>φo
(2)φi<φo
(3)φi=−φo
(4)φi=φo
98.
The electric current in a circular coil of four turns produces a magnetic induction 32 T at its center. The coil is unwound and is rewound into a circular coil of single turn, the magnetic induction at the center of the coil by the same current will be
(1)8T
(2)4T
(3)2T
(4)16T
99.
A solenoid 1.5m long and 0.4cm in diameter possesses 10 turns per cm length. A current of 5A falls through it. The magnetic field at the axis inside the solenoid is
(1)2π×10−3T
(2)2π×10−5T
(3)4π×10−2T
(4)4π×10−3T
100.
A plane electromagnetic wave of frequency 25GHz is propagating in vacuum along the z-direction. At a particular point in space and time, the magnetic field is given by B→=5×10−8j^T. The corresponding electric field E is (Speed of light c=3×108ms−1 )
(1)1.66×10−18i^V/m
(2)15i^V/m
(3)−15i^V/m
(4)18i^V/m
101.
A 50cm long solenoid has winding of 400 turns. What current must pass through it to produce a magnetic field of induction 4π×10−3T at the centre ?
(1)10.5A
(2)12.5A
(3)25.0A
(4)20.0A
102.
A magnetic needle of magnetic moment 6.7 × 10–2Am2 and moment of inertia 7.5 × 10–6 kg m2 is performing simple harmonic oscillations in a magnetic field of 0.01 T. Time taken for 10 complete oscillations is:
(1)8.76 s
(2)6.65 s
(3)8.89 s
(4)6.98 s
103.
A circular current loop of magnetic moment M is in an arbitrary orientation in an external uniform magnetic ficld B. The work done to rotate the loop by 30∘ about an axis perpendicular to its plane is
(1)MB2
(2)MB
(3)Zero
(4)3MB2
104.
A coil is placed perpendicular to a magnetic field of 5000T. When the field is changed to 3000T in 2s, an induced emf of 22V is produced in the coil. If the diameter of the coil is 0.02m, then the number of turns in the coil is:
(1)7
(2)70
(3)35
(4)140
105.
In the product F=q(v×B)=qv×(Bi+Bj+B0k) For q=1 and v=2i+4j+6k and F=4i−20j+12k What will be the complete expression for B ? [NEET 2021]
(1)−8i−8j−6k
(2)−6i−6j−8k
(3)8i+8j−6k
(4)6i+6j−8k
106.
In an experiment, electrons are accelerated, from rest, by applying a voltage of 500V. Calculate the radius of the path if a magnetic field 100mT is then applied. [Charge of the electron =1.6×10−19C Mass of the electron (=9.1×10−31kg)
(1)7.5×10−3m
(2)7.5×10−2m
(3)7.5m
(4)7.5×10−4m
107.
A circular coil of wire of radius ' r ' has ' n ' turns and carries current ' ?. The magnetic induction ' B ' at a point on the axis of the coil at a distance 3r from its centre is
(1)16rμ0nI
(2)32rμ0nI
(3)4rμ0nI
(4)8rμ0nI
108.
A circular coil carrying current ' l ' has radius ' R ' and magnetic field at the centre is ' B '. At what distance from the centre along the axis of the same coil, the magnetic field will be 8B ?
(1)R2
(2)R3
(3)2R
(4)3R
109.
Two long parallel wires are at a distance of 1 meter. Both of them carry one ampere of current. The force of attraction per unit length between the two wires is
(1)5×10−8N/m
(2)2×10−8N/m
(3)2×10−7N/m
(4)10−7N/m
110.
A cyclotron's oscillator frequency is 10MHz and the operating magnetic field is 0.66T. If the radius of its dees is 60cm, then the kinetic energy of the proton beam produced by the accelerator is
(1)9MeV
(2)10MeV
(3)7MeV
(4)11MeV
111.
A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B, at a radial distances a/2 and 2a respectively, from the axis of the wire is:
(1)4
(2)41
(3)21
(4)1
112.
A range of galvanometer is ' V ', when 50Ω resistance is connected in series. Its range gets doubled when 500Ω resistance is connected in series. Galvanometer resistance is
(1)100Ω
(2)200Ω
(3)300Ω
(4)400Ω
113.
A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross‐section. The ratio of the magnetic fields B and B’, at radial distances a/2 and 2a respectively, from the axis of the wire is
(1)1
(2)4
(3)41
(4)21
114.
A galvanometer has a deflection of 25 divisions for a current of 0.1 A flowing through it. Then the current sensitivity of the galvanometer is
(1)25div/A
(2)250 div/A
(3)2.5div/A
(4)0.25div/A
115.
Magnetic field at the centre of a circular coil of radius R due to current I flowing through it is B. The magnetic field at a point along the axis at distance R from the centre is
(1)2B
(2)4B
(3)8B
(4)8b
116.
Two long parallel conducting wires carrying currents are separated by a distance ' x '. Work done per unit length in changing the distance between the wires is proportional to
(1)logex1
(2)x1
(3)logex
(4)x
117.
The electric field of a plane electromagnetic wave is given by E→=Eo2i^+j^cos(kz+ωt). At t=0, a positively charged particle is at the point (x,y,z)=(0,0,kπ). If its instantaneous velocity at (t=0) is vok^ , the force acting on it due to the wave is :
(1)f=0
(2)Antiparallel to 2i^+j^
(3)Parallel to 2i^+j^
(4)k^
118.
A proton and an α-particle (with their masses in the ration of 1 : 4 and charges in the ration of 1 : 2) are accelerated from rest through a potential difference V. If a uniform magnetic field (B) is set up perpendicular to their velocities, the ratio of the radii rp : rα of the circular paths described by them will be:
(1)1 : 3
(2)1:3
(3)1:2
(4)1 : 2
119.
Two parallel wires in free space are 10cm apart and each carries a current of 10A in the same direction. The force exerted by one wire on the other (per unit length) is
(1)2×10−4 N m-1 [attractive]
(2)2×10−7 N m-1 [attractive]
(3)2×10−4 N m-1 [repulsive]
(4)2×10−7 N m-1 [repulsive]
120.
Two parallel conductor each 50m long, separated by 0.2 m experience a force of 1N. If the current in the first conductor is twice that of the second conductor, then what is the current in the second conductor? (μ0=4π×10−7)
