Magnetic Field Due to Circular Current Carrying Wire - NEET Physics Questions
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Magnetic Field Due to Circular Current Carrying Wire

Practice Questions:
Question 1: moderate

An otherwise infinite, straight wire has two concentric loops of radii a and b carrying equal
currents in opposite directions as shown. The magnetic field at the common centre is zero for

1. \[\frac{a}{b}=\frac{\pi+1}{\pi}\]
2. \[\frac{a}{b}=\frac{\pi}{\pi+1}\]
3. \[\frac{a}{b}=\frac{\pi-1}{\pi+1}\]
4. \[\frac{a}{b}=\frac{\pi+1}{\pi-1}\]
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Question 2: moderate

A wire loop is formed by joining two sections of radii r1 and r2 subtending an angle ΞΈ at O. The magnetic field at O is B0.

1. \[B_{0}=\frac{\mu_{0}I}{4\pi}\left( \frac{1}{r_{1}}+\frac{1}{r_{2}} \right)\theta : outwards\]
2. \[B_{0}=\frac{\mu_{0}I}{4\pi}\left( \frac{1}{r_{1}}-\frac{1}{r_{2}} \right)\theta : inwards\]
3. \[B_{0}=\frac{\mu_{0}I}{2\pi}\left( \frac{1}{r_{1}}+\frac{1}{r_{2}} \right)\theta : outwards\]
4. \[B_{0}=\frac{\mu_{0}I}{2\pi}\left( \frac{1}{r_{1}}-\frac{1}{r_{2}} \right)\theta : inwards\]
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Question 3: moderate

A charge Q is uniformly distributed over the surface of non-conducting disc of radius R. The
disc rotates about an axis perpendicular to its plane and passing through its centre with an
angular velocity Ο‰. As a result of this rotation a magnetic field of induction B is obtained at
the centre of the disc. If we keep both the amount of charge placed on the disc and its
angular velocity to be constant and vary the radius of the disc then the variation of the
magnetic induction at the centre of the disc will be represented by the figure

1.
2.
3.
4.
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Question 4: moderate

A current I is flowing through the loop. The direction of the current and the shape of the loop are as shown in the figure. The magnetic field at the centre of the loop is (MA = R, MB = 2R, angle DMA = 90Β°)

1. \[\frac{7\mu_{0}i}{16R}\] , but out of the plane of the paper.
2. \[\frac{5\mu_{0}i}{16R}\] , but out of the plane of the paper.
3. \[\frac{7\mu_{0}i}{16R}\] , but into the plane of the paper.
4. \[\frac{5\mu_{0}i}{16R}\] , but into the plane of the paper.
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Question 5: moderate

A coil having N turns is would tightly in the form of a spiral with inner and outer radii a and b respectively. When a current I passes through the coil, the magnetic field at its centre is :

1. \[\frac{\mu_{0}NI}{b}\]
2. \[\frac{2\mu_{0}NI}{a}\]
3. \[\frac{\mu_{0}NI}{2\left( b-a \right)}log\frac{b}{a}\]
4. \[\frac{\mu_{0}NI}{\left( b-a \right)}log\frac{b}{a}\]
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Question 6: moderate

A particle carrying a charge equal to 100 times the charge on an electron is rotating per second in a circular path of radius 0.8m. The value of the magnetic field produced at the centre will be : (ΞΌ0 = permeability constant)

1. \[10^{-7}/\mu_{0}\]
2. \[10^{-17}\mu_{0}\]
3. \[10^{-6}/\mu_{0}\]
4. \[10^{-7}\mu_{0}\]
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Question 7: moderate

The magnetic induction at the centre O of the current carrying bent wire shown in the adjoining figure is :

1. \[\frac{\mu_{0}I}{4\pi R_{1}}\alpha\]
2. \[\frac{\mu_{0}I}{4\pi R_{2}}\alpha\]
3. \[\frac{\mu_{0}I\alpha}{4\pi}\left( \frac{1}{R_{1}}-\frac{1}{R_{2}} \right)\]
4. \[\frac{\mu_{0}I\alpha}{4\pi}\left( \frac{1}{R_{1}}+\frac{1}{R_{2}} \right)\]
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Question 8: moderate

A cell is connected between the points A and C of a circular conductor ABCD with O as centre and angle AOC = 60Β°. If B1 and B2 are the magnitudes of the magnetic fields at O due to the currents in ABC and ADC respectively, then ratio B1/B2 is :-

1. 1
2. 2
3. 5
4. 6
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Question 9: moderate

Figure shows three cases, in all cases the circular part has radius r and stragiht ones are infinitely long. For the same current the ratio of field B at center P in the three cases B1 : B2 : B3 is :

1. \[\left(- \frac{\pi}{2} \right):\left( \frac{\pi}{2} \right):\left( \frac{3\pi}{4}-\frac{1}{2} \right)\]
2. \[\left(- \frac{\pi}{2}+1 \right):\left( \frac{\pi}{2}+1 \right):\left( \frac{3\pi}{4}+\frac{1}{2} \right)\]
3. \[\left(- \frac{\pi}{2} \right):\left( \frac{\pi}{2} \right):\left( \frac{3\pi}{4} \right)\]
4. \[\left(- \frac{\pi}{2}-1 \right):\left( \frac{\pi}{2}-\frac{1}{4} \right):\left( \frac{3\pi}{4}+\frac{1}{2} \right)\]
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Question 10: moderate

Two very thin metallic wires placed along X and Y-axis carry equal currents as shown in figure. AB and CD are lines at 45ΒΊ with the axes with origin of axes of O. The magnetic fields will be zero on the line :

1. AB
2. CD
3. Segment OB only of line AB
4. Segment OC only of line CD
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