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 2. 1
3. 4 4. 1/4

Subtopic:  Ampere Circuital Law |
 57%
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 |
 70%
From NCERT
NEET - 2015
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A circuit contains an ammeter, a battery of 30 V and a resistance 40.8Ω all connected in series. If the ammeter has a coil of resistance 480Ω  and a shunt of 20Ω then reading in the ammeter will be :

(1) 0.5A

(2) 0.25A

(3) 2A

(4) 1A

Subtopic:  Conversion to Ammeter & Voltmeter |
 63%
From NCERT
NEET - 2015
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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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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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A millivoltmeter of 25 mV range is to be converted into an ammeter of 25 A range. The value (in ohm) of necessary shunt will be:

(1)0.001                                     

(2)0.01

(3)1                                           

(4)0.05

Subtopic:  Conversion to Ammeter & Voltmeter |
 79%
From NCERT
NEET - 2012
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An alternating electric field of frequency v, is applied across the dees (radius=R) of a cyclotron that is being used to accelerate protons(mass=m).The operating magnetic field (B) used in the cyclotron and the kinetic energy (K) of the proton beam, produced by it, are given by

(1)B=mve and K=2mπ2v2R2

(2)B=2πmve and K=m2πvR2

(3)B=2πmve and K=2mπ2v2R2

(4)B=mve and K=m2πvR2

Subtopic:  Lorentz Force |
 74%
From NCERT
NEET - 2012
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