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 \(\frac{a}{2}\) and \(2a\) respectively, from the axis of the wire, is:
1. \(\frac{1}{2}\) 2. \(1\)
3. \(4\) 4. \(\frac{1}{4}\)

Subtopic:  Ampere Circuital Law |
 58%
From NCERT
NEET - 2016
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A wire carrying current l has the shape as shown in the adjoining figure. Linear parts of the wire are very long and parallel to X-axis while the semicircular portion of radius R is lying in the Y-Z plane. Magnetic field at point O is :


1. B=μ04π×iRπi^+2k^

2. B=-μ04π×iRπi^-2k^

3. B=-μ04π×iRπi^+2k^

4. B=μ04π×iRπi^-2k^

Subtopic:  Magnetic Field due to various cases |
 62%
NEET - 2015
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An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude:

1. μ0ne2πr
2. Zero
3. n2er
4. μ0ne2r

Subtopic:  Magnetic Field due to various cases | Lorentz Force |
 63%
From NCERT
NEET - 2015
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A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to the field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV, the energy acquired by the alpha particle will be

(1)4 MeV

(2) 0.5 MeV

(3) 1.5 MeV

(4) 1 MeV

Subtopic:  Lorentz Force |
 71%
From NCERT
NEET - 2015
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A rectangular coil of length 0.12 m and width 0.1 m having 50 turns of wire is suspended vertically in a uniform magnetic field of strength 0.2 Wb/m2. The coil carries a current of 2 A. If the plane of the coil is inclined at an angle of 30° with the direction of the field, the torque required to keep the coil in stable equilibrium will be:

1. 0.15 Nm

2. 0.20 Nm

3. 0.24 Nm

4. 0.12 Nm

Subtopic:  Magnetic Moment |
NEET - 2015
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In an ammeter 0.2% of main current passes through the galvanometer. If resistance of galvanometer is G, the resistance of ammeter will be

(1) 1499G

(2) 499500G

(3) 1500G

(4) 500499G

Subtopic:  Moving Coil Galvanometer |
From NCERT
NEET - 2014
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Two identical long conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry  Iand I2 currents, respectively. Point P is lying at distance d from 0 along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be

(1) μo/2πd(I1/I2)

(2)μo/2πd (I1+I2)

(3)μo/2πd(I12-I22)

(4)μo/2πd(I12+I22)1/2


Subtopic:  Magnetic Field due to various cases |
 77%
From NCERT
NEET - 2014
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A current loop in a magnetic field

(1) experiences a torque whether the field is uniform or non-uniform in all orientations

(2) can be in equilibrium in one orentations.

(3) can be equilibrium in two orientations, both the wquilibriu states are unstable

(4) can be in equilibrium in two orientations, one stable while the other is unstable



Subtopic:  Magnetic Field due to various cases | Current Carrying Loop: Force & Torque |
 67%
From NCERT
NEET - 2013
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A bar magnet of length L and magnetic dipole moment M is bent in the form of an are as shown in figure. The new magnetic dipole moment will be


(1)M

(2)3M/π

(3)2/πM

(4)M/2

Subtopic:  Bar Magnet |
 78%
NEET - 2013
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Two similar coils of radius R are lying concentrically with their planes at right angles to each other. The currents flowing in them are I and 2I, respectively. The resultant magnetic field induction at the centre will be 

(1)5μ0I2R                                         

(2)3μ0I2R

(3)μ0I2R                                             

(4)μ0IR

Subtopic:  Magnetic Field due to various cases |
 79%
From NCERT
NEET - 2012
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