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Physics NEET MCQ
Magnetic Effects Of Current Mcq
Quiz 9
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Q.1
The earth's magnetic induction at certain point is 7 × 10-5 Wb/mthis is to be annulled by the magnetic induction at the centre of a circular conducting loop of radius 10 cm. The required current in the loop is ....
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a) 0.11A
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b) 0.05A
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c)11.15 A
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d)0.5A
Explanation
Answer: (c)
Q.2
If a loop placed near a straight wire is free to move under the magnetic force, then the loop .....
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a) remains stationary
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b) moves away from the wire
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c)moves towards the wire
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d)rotate around the wire
Explanation
Answer:(c)
Q.3
If a charged particle enters in a region of uniform electric field parallel to the direction of the magnetic field, then the particle will move in a ........
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a) straight line
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b) circle
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c) helix
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d) cycloid
Explanation
Answer: (a)
Q.4
A circular coil carrying current has a radius R.The distance from the centre of the coil, on the axis where the magnetic induction will be (1/8)th of its value at the centre of the coil, is .....
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a)R/ √3
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b) R√3
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c)2R√3
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d)(2/√3)R
Explanation
Answer: (b)
Q.5
A charged particle enters in a uniform magnetic field perpendicular to the direction of the field. the radius of curvature of the path of the charged particle is proportional to .....
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a) the charge on the particle
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b) the momentum of the particle
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c)the energy of the particle
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d)the intensity of the field
Explanation
Answer: (b)
Q.6
A proton and α-particle are projected with same kinetic energy at right angle to a uniform magnetic field. Which of the following statement will be true
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a) α-particle will bend in a circular path smaller radius that of proton
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b) the radius of the path of α-particle will be greater than that of the proton
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c)α-particle and proton will move along the circular path with the same radius
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d)Both particles will go along a straight path through the magnetic field
Explanation
We know that r ∝ p/q ∴ r ∝ (√2mK) / q since K is same R ∝ √m/q Answer:(c)
Q.7
A particle carrying a charge equal to 100 times the charge one electron is rotating per second in a circular path of radius 0.8 m. The value of magnetic field produced at the centre will be .....
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a) 10-7 / µo
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b) 10-17 µo
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c) 10-6 µo
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d) 10-7 µo
Explanation
q=100e, f=1 I qf=100e B=µoI/2a Answer: (b)
Q.8
A beam of ion with velocity 2 ×105 m/s, enters perpendicularly to a uniform magnetic field of 4 ×10-2 Tesla. If the specific charge of the ion is 5 ×10-7 C/ kg, the radius of the circular path will be ....
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a)0.1 m
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b) 0.16 m
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c)0.2 m
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d)0.25 m
Explanation
use r=mv/eB, given e/m=5 ×10-7 C/ kg,Answer: (a)
Q.9
Two long conductor which are parallel are placed at right angles to a meter scale at 1cm and 9 cm mark. They carry current I and 4I respectively in the same direction. The resultant magnetic field due to them is zero at ....
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a) 1.6 cm mark
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b) 2.6 cm mark
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c)4.6 cm mark
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d)6.4 cm mark
Explanation
Magnetic field at null point due to Iamp conductor=magnetic field due to 4I current Thus magnetic field will be zero at 1.6+1cm=2.6 cm markAnswer: (b)
Q.10
Two circular coils have number of turns in the ratio of 1:2 and their radii are in the ratio 2:If the same current flows through them, the magnetic field at their centres will be in ratio
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a) 1:1
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b) 1:2
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c) 2:1
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d) 1:4
Explanation
B ∝ N / r Answer:(d)
Q.11
1 web/m2 is equal to ....
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a) 104 gauss
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b) 102 gauss
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c) 10-2 gauss
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d) 10-4 gauss
Explanation
Answer: (a)
Q.12
A proton and an α-particle enter a uniform magnetic field perpendicularly, with the same speed. If the proton takes 20µs to complete one revolution, then the periodic time for α-particle is ......
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a)20 µs
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b) 40 µs
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c)10 µs
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d)30 µs
Explanation
r=mv/Bq v=Bqr/m But v=2πr/T 2πr/T=Bqr/m T=2πm/Bq T ∝ m/q , B is constant same for both particle∴Answer: (b)
Q.13
A long straight wire carries a current of 10A. An electron travels with a speed of 5×106 m/s parallel to the wire, 0.1 m away from it. the force exerted by the magnetic field of the current on the electron is
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a) 1.6 ×10-18 N
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b) 1.6 ×10-17 N
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c)3.2 ×10-17 N
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d)3.2 ×10-18 N
Explanation
Answer: (a)
Q.14
TWo long staright wires each carrying a current I, are separated by a distance r. If the currents are in opposite directions, then the strength of the magnetic field at a point midway between two wires is .....
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a) µoI / πr
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b) 2µoI / πr
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c)µoI / 2πr
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d)zero
Explanation
Answer:(b)
Q.15
The current sensitivity of moving coil Galvanometer is inversely proportional to .........
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a) the number of turns of the coil
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b) the moment of inertia of the coil
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c) strength of magnetic field
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d) the torsional constant of the suspension fibre
Explanation
current sensitivity ∝ φ / I Answer: (d)
Q.16
Which of the following cannot be accelerated by a cyclotron?
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a)α-particle
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b) proton
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c)electron
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d)neutron
Explanation
Answer: (d)
Q.17
Two concentric coils carry the same current in opposite directions. the diameter of the inner coil is half that of the outer coil. If the magnetic field produced by the outer coil at the common centre is1 T, the net field at the centre is
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a) 1 T
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b) 2 T
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c)3 T
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d)4 T
Explanation
Ent field will be B2 - B1Answer: (a)
Q.18
The dipole moment of current carrying loop is independent of
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a) current in the loop
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b) number of turns
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c)area of loop
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d)magnetic field in which it is situated
Explanation
Answer:(d)
Q.19
No force is experienced by a magnetic field on a stationary.........
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a) current loop
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b) electric dipole
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c) magnetic dipole
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d) all of them
Explanation
Answer: (b)
Q.20
Two long parallel wires, separated by a distance r have equal current flowing through both. The magnetic field of one exerts a force on the other. the distance r is doubled and current in each wire is reduced to I/What id the force between them now ?
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a)F
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b) 4F
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c)F/4
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d)F/8
Explanation
Answer: (d)
Q.21
In the expression of Lorenz force, which of the quantities out of F, v and B are always perpendicular
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a) v and B
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b) F and v
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c)F and B
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d)both (b) and (c)
Explanation
Answer: (d)
Q.22
Magnetic field at the centre of a circular loop of area A is B. The magnetic moment of the loop is ............
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a)
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b)
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c)
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d)
Explanation
B=µo I / (2R) I=2BR/µo Magnetic moment=IA Answer:(d)
Q.23
A positive charge is moving upwards in manetic field which is towards north. The particle will be deflected towards .........
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a) east
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b) west
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c) north
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d) south
Explanation
Answer: (b)
Q.24
A uniform magnetic field is at right angle to the direction of motion of proton. As a result, the proton describes a circular path of radius 2.5 cm. If the speed of the proton is doubled then the radius of the circular path will be ...
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a)0.5 cm
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b) 2.5 cm
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c)5.0 cm
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d)7.5 cm
Explanation
we know that r ∝ v Answer: (c)
Q.25
On connecting a battery to the two corners of a diagonal of a square conductor frame of side a, the magnetic field at the centre will be .....
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a) zero
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b) µo / πa
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c)2µo / πa
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d)(4µo I)/ πa
Explanation
Answer: (a)
Q.26
TWo infinitely long thin insulated wire lie in the XY plane along the X and Y axis respectively. In each wire a current I flows respectively above the positive X and Y direction respectively. The locus of a point in this plane where the magnetic field is zero is given by.....
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a)y2 x
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b) x=y 2
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c)x=y
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d)x + y=0
Explanation
Answer:(c)
Q.27
The radius of a circular coil carrying current is 'a'. The magnetic field at the centre is B1 and magnetic field at its axis at a distance 'a' from its centre is B2 Then B1:B2=.....
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a) √2 : 2
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b) 1:2√2
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c) 2√2:1
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d) 2:√2
Explanation
Answer: (c)
Q.28
Two thin parallel wires are at a distance b from each other. Current through each wire is i. What will be the value of force acting per unit length of the wire
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a)µo i2 / πb
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b) µo i2 / 2πb
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c)µo i / 2πb
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d)µo i / 2πb2
Explanation
use formula F=µo I1I2 l / 2π dAnswer: (b)
Q.29
In a straight current carrying conductor, √5 A current is flowing. Magnetic field intensity at a point on the perpendicular bisector and at a distance equal to length of the wire is ........ T [ LEngth of wire is 1m]
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a) 2 ×10-7
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b) 4 × 10-7
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c)10-7
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d)zero
Explanation
Answer: (a)
Q.30
An electron experiences a force ( 4.0 i + 3.0 j) ×10-13 N in an uniform magnetic field when its velocity is along 2.5k ×107 m/s. When the velocity is redirected and becomes (1.5i - 2.0 j) × 107 m/s, the magnetic force on the electron in zero. the magnetic field vector B is ......
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a) 1i - 0.075j
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b) -1i - 0.075j
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c) 0.075i - 0.075j + k
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d)0.075i - 0.1j
Explanation
Cross product of v and B is zero Answer:(d)
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