Moving Charges and Magnetism
83 Board Physics previous year questions on Moving Charges and Magnetism — options free on every question; 8 include the answer & explanation free, the rest unlock with PYQ Pass.
A 1 cm segment of a wire lying along x -axis carries current of 0.5 A along +x direction. A magnetic field \(\vec{B}=(0.4\mathrm{mT})\hat{j}+(0.6\mathrm{mT})\hat{k}\) is switched on, in the region. The force acting on the segment is
\((-3\hat{j}+2\hat{k})\mu \mathrm{N}\)
A wire of length 4.4 m is bent round in the shape of a circular loop and carries a current of 1.0 A . The magnetic moment of the loop will be :
\(1.54{\mathrm{Am}}^{2}\)
The magnetic moment M of a current-carrying loop is given by:M=IA,
where I is the current and A is the area of the loop. The area of a circular loop is:A=π\({r}^{2}\).
The circumference of the loop is 2πr=4.4m,
so:r=\(\frac{4.4}{2\pi }\)=0.7m.
Now, calculating the area:A=π(\(0.{7}^{2}\))=1.54
Thus, the magnetic moment is:M=1.0×1.54=1.54A\({m}^{2}\).
A straight wire is kept horizontally along east-west direction. If a steady current flows in wire from east to west, the magnetic field at a point above the wire will point towards
North
\(B=\frac{{\mu }_{0}i}{2\pi r}\)
from Right hand thumb rule, direction of B is North.
A straight wire is kept horizontally along east-west direction. If a steady current flows in wire from east to west, the magnetic field at a point above the wire will point towards
North
\(B=\frac{{\mu }_{0}i}{2\pi r}\)
from Right hand thumb rule, direction of B is North.
A proton is moving with a uniform velocity of \(2\times 1{0}^{8}\text{ }\text{m/s}\) in uniform magnetic and electric fields, which are perpendicular to each other. If the electric field is switched off, the proton moves in a circular path of radius \(1.6\times 1{0}^{−5}\text{ }\text{m}\). The magnetic field (\(B\)) is:
(Shift II Memory Based)
\(1.3\times 1{0}^{5}\text{ }\text{T}\)
When the electric field is switched off, the magnetic force provides the centripetal force required for circular motion. The magnetic force acting on the proton is given by:
\({\mathrm{F}}_{\mathrm{m}}=\mathrm{qvB}\sin 90^\circ =\mathrm{qvB}\) ..... (1)
The centripetal force is given by
\(\mathrm{Fc}=\frac{{\mathrm{mv}}^{2}}{\mathrm{r}}\) .... (2)
By equating equation (1) and (2), we get
\(\mathrm{qvB}=\frac{{\mathrm{mv}}^{2}}{\mathrm{r}}\\ \mathrm{B}=\frac{\mathrm{m}\mathrm{v}}{\mathrm{r}\mathrm{q}}\\ \mathrm{B}=\frac{1.67\times {10}^{-27}\times 2\times {10}^{8}}{1.6\times {10}^{-5}\times 1.6\times {10}^{-19}}\\ \mathrm{B}=1.3\times {10}^{5}\mathrm{T}\)
A 1 cm segment of a wire lying along x -axis carries current of 0.5 A along +x direction. A magnetic field \(\vec{B}=(0.4\mathrm{mT})\hat{j}+(0.6\mathrm{mT})\hat{k}\) is switched on, in the region. The force acting on the segment is
\((-3\hat{j}+2\hat{k})\mu \mathrm{N}\)
A galvanometer of resistance \(G \Omega\) is converted into an ammeter of range 0 to IA. If the current through the galvanometer is \(0.1 \%\) of I A, the resistance of the ammeter is :
\(\frac{ G }{1000} \Omega\)
$$\begin{aligned}& \text{Given: Galvanometer resistance } = G\ \Omega, \quad \text{Full-scale current } = I\ \mathrm{A}, \\[3pt]& \text{Current through galvanometer } = 0.1\% \text{ of } I = \frac{0.1}{100}I = \frac{I}{1000}. \\[6pt]& \text{Let shunt resistance } = S. \text{ Then the same potential difference acts across } G \text{ and } S. \\[3pt]& \text{So, } I_g G = I_s S, \quad \text{where } I_s = I - I_g = I - \frac{I}{1000} = \frac{999I}{1000}. \\[4pt]& \Rightarrow S = \frac{I_g G}{I_s} = \frac{\frac{I}{1000} G}{\frac{999I}{1000}} = \frac{G}{999}. \\[6pt]& \text{The equivalent resistance of the ammeter is } R_A = G \parallel S \\[4pt]& R_A = \frac{G \times S}{G + S} = \frac{G \times \frac{G}{999}}{G + \frac{G}{999}} = \frac{G^2 / 999}{G(1 + 1/999)} \\[4pt]& R_A = \frac{G / 999}{1 + 1/999} = \frac{G / 999}{1000/999} = \frac{G}{1000}. \\[6pt]& \boxed{R_A = \frac{G}{1000}} \\[4pt]& \text{Hence, the resistance of the ammeter is } \boxed{\tfrac{G}{1000}\ \Omega.}\end{aligned}$$
A straight wire is kept horizontally along east-west direction. If a steady current flows in wire from east to west, the magnetic field at a point above the wire will point towards
North
\(B=\frac{{\mu }_{0}i}{2\pi r}\)
from Right hand thumb rule, direction of B is North.
A galvanometer of resistance \(G \Omega\) is converted into an ammeter of range 0 to IA. If the current through the galvanometer is \(0.1 \%\) of I A, the resistance of the ammeter is :
Options are free to see. Unlock the correct answer and full explanation with Pass.
A galvanometer of resistance \(100 \Omega\) is converted into an ammeter of range \((0-1 A)\) using a resistance of \(0.1 \Omega\). The ammeter will show full scale deflection for a current of about
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A galvanometer of resistance \(50\Omega\) is converted into a voltmeter of range ( \(0-2\mathrm{V}\) ) using a resistor of \(1.0\mathrm{k}\Omega\). If it is to be converted into a voltmeter of range \((0-10\mathrm{V})\), the resistance required will be
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A current carrying circular loop of magnetic moment \(\vec{M}\) is suspended in a vertical plane in an external magnetic field \(\vec{B}\) such that its plane is normal to \(\overrightarrow{ B }\). The work done in rotating this loop by \(45^{\circ}\) about an axis perpendicular to \(\vec{B}\) is closest to :
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An electron projected perpendicular to a uniform magnetic field B moves in a circle. If Bohr's quantization is applicable, then the radius of the electronic orbit in the first excited state is :
[JEE Main 2025, 22 Jan (Shift 2)]
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A 10 cm long wire lies along y-axis. It carries a current of 1.0 A in positive y-direction. A magnetic field \(\vec{B}=(5 mT ) \hat{j}-(8 mT ) \hat{k}\) exists in the region. The force on the wire is :
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An electron projected perpendicular to a uniform magnetic field B moves in a circle. If Bohr's quantization is applicable, then the radius of the electronic orbit in the first excited state is :
[JEE Main 2025, 22 Jan (Shift 2)]
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A 1 cm segment of a wire lying along x-axis carries current of 0.5 A along \(+x\) direction. A magnetic field \(\vec{B}=\left(0.4mT\right)\hat{j}+(0.6mT)\hat{k}\) is switched on, in the region. The force acting on the segment is
Options are free to see. Unlock the correct answer and full explanation with Pass.
A galvanometer of resistance \(100 \Omega\) is converted into an ammeter of range \((0-1 A)\) using a resistance of \(0.1 \Omega\). The ammeter will show full scale deflection for a current of about
Options are free to see. Unlock the correct answer and full explanation with Pass.
A current carrying circular loop of magnetic moment \(\vec{M}\) is suspended in a vertical plane in an external magnetic field \(\vec{B}\) such that its plane is normal to \(\overrightarrow{ B }\). The work done in rotating this loop by \(45^{\circ}\) about an axis perpendicular to \(\vec{B}\) is closest to :
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Two charged particles, \(P\) and \(Q\), each having charge \(q\) but of masses m1 and m2 are accelerated through the same potential difference V. They enter a region of magnetic field \(\vec{\mathrm{B}}(⊥\vec{\mathrm{v}})\) and describe the circular paths of radii \(a\) and \(b\) respectively. Then \(\left(\frac{{m}_{1}}{{m}_{2}}\right)\) is equal to :
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A galvanometer of resistance \(G \Omega\) is converted into an ammeter of range 0 to IA. If the current through the galvanometer is \(0.1 \%\) of I A, the resistance of the ammeter is :
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A galvanometer of resistance \(\mathrm{G}\Omega\) is converted into an ammeter of range 0 to I A. If the current through the galvanometer is \(0.1\%\) of I A , the resistance of the ammeter is :
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A straight wire is kept horizontally along east-west direction. If a steady current flows in wire from east to west, the magnetic field at a point above the wire will point towards
Options are free to see. Unlock the correct answer and full explanation with Pass.
A circular loop of wire, carrying a current \(I\) ' is lying in xy-plane with its centre coinciding with the origin. It is subjected to a uniform magnetic field pointing along + z -axis. The loop will :
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A current carrying circular loop of magnetic moment \(\vec{M}\) is suspended in a vertical plane in an external magnetic field \(\vec{B}\) such that its plane is normal to \(\overrightarrow{ B }\). The work done in rotating this loop by \(45^{\circ}\) about an axis perpendicular to \(\vec{B}\) is closest to :
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An electron projected perpendicular to a uniform magnetic field B moves in a circle. If Bohr's quantization is applicable, then the radius of the electronic orbit in the first excited state is :
[JEE Main 2025, 22 Jan (Shift 2)]
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A galvanometer of resistance \(50\Omega\) is converted into a voltmeter of range ( \(0-2\mathrm{V}\) ) using a resistor of \(1.0\mathrm{k}\Omega\). If it is to be converted into a voltmeter of range \((0-10\mathrm{V})\), the resistance required will be
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An electron projected perpendicular to a uniform magnetic field B moves in a circle. If Bohr's quantization is applicable, then the radius of the electronic orbit in the first excited state is :
[JEE Main 2025, 22 Jan (Shift 2)]
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A straight wire of length 1.0 m is placed along x -axis, in a region with magnetic field \(\vec{B}=(3\hat{i}+2\hat{j})T\). A current of 2.0 A flows in the wire along \(+x\) direction. The magnetic force acting on the wire is :
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A loop carrying a current I clockwise is placed in \(x-y\) plane, in a uniform magnetic field directed along \(z\)-axis. The tendency of the loop will be to :
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A 10 cm long wire lies along y-axis. It carries a current of 1.0 A in positive y-direction. A magnetic field \(\vec{B}=(5\mathrm{mT})\hat{j}-(8\mathrm{mT})\hat{k}\) exists in the region. The force on the wire is :
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A particle of mass \(m\) and charge \(q\)describes a circular path of radius \(R\) in a magnetic field. If its mass and charge were 2 m and \(\frac{q}{2}\) respectively, the radius of its path would be
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A straight wire of length 1.0 m is placed along x -axis, in a region with magnetic field \(\vec{B}=(3\hat{i}+2\hat{j})T\). A current of 2.0 A flows in the wire along \(+x\) direction. The magnetic force acting on the wire is :
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A galvanometer of resistance \(100 \Omega\) is converted into an ammeter of range \((0-1 A)\) using a resistance of \(0.1 \Omega\). The ammeter will show full scale deflection for a current of about
Options are free to see. Unlock the correct answer and full explanation with Pass.
A loop carrying a current I clockwise is placed in \(x-y\) plane, in a uniform magnetic field directed along \(z\)-axis. The tendency of the loop will be to :
Options are free to see. Unlock the correct answer and full explanation with Pass.
A galvanometer of resistance \(50\Omega\) is converted into a voltmeter of range ( \(0-2\mathrm{V}\) ) using a resistor of \(1.0\mathrm{k}\Omega\). If it is to be converted into a voltmeter of range \((0-10\mathrm{V})\), the resistance required will be
Options are free to see. Unlock the correct answer and full explanation with Pass.
Two charged particles, \(P\) and \(Q\), each having charge \(q\) but of masses m1 and m2 are accelerated through the same potential difference V. They enter a region of magnetic field \(\vec{\mathrm{B}}(⊥\vec{\mathrm{v}})\) and describe the circular paths of radii \(a\) and \(b\) respectively. Then \(\left(\frac{{m}_{1}}{{m}_{2}}\right)\) is equal to :
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A 1 cm segment of a wire lying along x-axis carries current of 0.5 A along \(+x\) direction. A magnetic field \(\vec{B}=\left(0.4mT\right)\hat{j}+(0.6mT)\hat{k}\) is switched on, in the region. The force acting on the segment is
Options are free to see. Unlock the correct answer and full explanation with Pass.
A loop carrying a current I clockwise is placed in \(x-y\) plane, in a uniform magnetic field directed along \(z\)-axis. The tendency of the loop will be to :
Options are free to see. Unlock the correct answer and full explanation with Pass.
A particle of mass \(m\) and charge \(q\)describes a circular path of radius \(R\) in a magnetic field. If its mass and charge were 2 m and \(\frac{q}{2}\) respectively, the radius of its path would be
Options are free to see. Unlock the correct answer and full explanation with Pass.
A 10 cm long wire lies along y-axis. It carries a current of 1.0 A in positive y-direction. A magnetic field \(\vec{B}=(5\mathrm{mT})\hat{j}-(8\mathrm{mT})\hat{k}\) exists in the region. The force on the wire is :
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A current carrying circular loop of magnetic moment \(\vec{M}\) is suspended in a vertical plane in an external magnetic field \(\vec{B}\) such that its plane is normal to \(\overrightarrow{ B }\). The work done in rotating this loop by \(45^{\circ}\) about an axis perpendicular to \(\vec{B}\) is closest to :
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A galvanometer of resistance \(G \Omega\) is converted into an ammeter of range 0 to IA. If the current through the galvanometer is \(0.1 \%\) of I A, the resistance of the ammeter is :
Options are free to see. Unlock the correct answer and full explanation with Pass.
Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : A electron in a certain region of uniform magnetic field is moving with constant velocity in a straight line path.
Reason (R): The magnetic field in that region is along the direction of velocity of the electron. In the light of the above statements, choose the correct answer from the options given below :
[JEE Main 2025, 24 Jan (Shift 2)]
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A circular loop of wire, carrying a current \(I\) ' is lying in xy-plane with its centre coinciding with the origin. It is subjected to a uniform magnetic field pointing along + z -axis. The loop will :
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A 1 cm segment of a wire lying along x -axis carries current of 0.5 A along +x direction. A magnetic field \(\vec{B}=(0.4\mathrm{mT})\hat{j}+(0.6\mathrm{mT})\hat{k}\) is switched on, in the region. The force acting on the segment is
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A straight wire of length 1.0 m is placed along x -axis, in a region with magnetic field \(\vec{B}=(3\hat{i}+2\hat{j})T\). A current of 2.0 A flows in the wire along \(+x\) direction. The magnetic force acting on the wire is :
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A 10 cm long wire lies along y-axis. It carries a current of 1.0 A in positive y-direction. A magnetic field \(\vec{B}=(5\mathrm{mT})\hat{j}-(8\mathrm{mT})\hat{k}\) exists in the region. The force on the wire is :
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A galvanometer of resistance \(G \Omega\) is converted into an ammeter of range 0 to IA. If the current through the galvanometer is \(0.1 \%\) of I A, the resistance of the ammeter is :
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A \(2\) amp current is flowing through two small circular copper coils having radii ratio \(1:2\). The ratio of their respective magnetic moments will be
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A 10 cm long wire lies along y-axis. It carries a current of 1.0 A in positive y-direction. A magnetic field \(\vec{B}=(5 mT ) \hat{j}-(8 mT ) \hat{k}\) exists in the region. The force on the wire is :
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A particle of mass \(m\) and charge \(q\)describes a circular path of radius \(R\) in a magnetic field. If its mass and charge were 2 m and \(\frac{q}{2}\) respectively, the radius of its path would be
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An electron enters a uniform magnetic field with speed \(v\). It describes a semicircular path and comes out of the field. The final speed of the electron is :
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A circular loop of wire, carrying a current \(I\) ' is lying in xy-plane with its centre coinciding with the origin. It is subjected to a uniform magnetic field pointing along + z -axis. The loop will :
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An equilateral triangle frame of side \(l\) is carrying current \(i\), find magnetic field at its centroid
(Shift - II Memory Based)
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Two charged particles, \(P\) and \(Q\), each having charge \(q\) but of masses m1 and m2 are accelerated through the same potential difference V. They enter a region of magnetic field \(\vec{\mathrm{B}}(⊥\vec{\mathrm{v}})\) and describe the circular paths of radii \(a\) and \(b\) respectively. Then \(\left(\frac{{m}_{1}}{{m}_{2}}\right)\) is equal to :
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A galvanometer of resistance \(\mathrm{G}\Omega\) is converted into an ammeter of range 0 to I A. If the current through the galvanometer is \(0.1\%\) of I A , the resistance of the ammeter is :
Options are free to see. Unlock the correct answer and full explanation with Pass.
A galvanometer of resistance \(\mathrm{G}\Omega\) is converted into an ammeter of range 0 to I A. If the current through the galvanometer is \(0.1\%\) of I A , the resistance of the ammeter is :
Options are free to see. Unlock the correct answer and full explanation with Pass.
A current carrying circular loop of magnetic moment \(\vec{M}\) is suspended in a vertical plane in an external magnetic field \(\vec{B}\) such that its plane is normal to \(\overrightarrow{ B }\). The work done in rotating this loop by \(45^{\circ}\) about an axis perpendicular to \(\vec{B}\) is closest to :
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A galvanometer of resistance \(50\Omega\) is converted into a voltmeter of range ( \(0-2\mathrm{V}\) ) using a resistor of \(1.0\mathrm{k}\Omega\). If it is to be converted into a voltmeter of range \((0-10\mathrm{V})\), the resistance required will be
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Consider a long straight wire of a circular cross-section (radius a) carrying a steady current I. The current is uniformly distributed across this cross-section. The distances from the centre of the wire's cross-section at which the magnetic field [inside the wire, outside the wire] is half of the maximum possible magnetic field, any where due to the wire, will be
[JEE Main 2025, 29 Jan (Shift 1)]
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A wire of length 4.4 m is bent round in the shape of a circular loop and carries a current of 1.0 A . The magnetic moment of the loop will be :
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Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : A electron in a certain region of uniform magnetic field is moving with constant velocity in a straight line path.
Reason (R): The magnetic field in that region is along the direction of velocity of the electron. In the light of the above statements, choose the correct answer from the options given below :
[JEE Main 2025, 24 Jan (Shift 2)]
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Two charged particles, \(P\) and \(Q\), each having charge \(q\) but of masses m1 and m2 are accelerated through the same potential difference V. They enter a region of magnetic field \(\vec{\mathrm{B}}(⊥\vec{\mathrm{v}})\) and describe the circular paths of radii \(a\) and \(b\) respectively. Then \(\left(\frac{{m}_{1}}{{m}_{2}}\right)\) is equal to :
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A 1 cm segment of a wire lying along x-axis carries current of 0.5 A along \(+x\) direction. A magnetic field \(\vec{B}=\left(0.4mT\right)\hat{j}+(0.6mT)\hat{k}\) is switched on, in the region. The force acting on the segment is
Options are free to see. Unlock the correct answer and full explanation with Pass.
A galvanometer of resistance \(\mathrm{G}\Omega\) is converted into an ammeter of range 0 to I A. If the current through the galvanometer is \(0.1\%\) of I A , the resistance of the ammeter is :
Options are free to see. Unlock the correct answer and full explanation with Pass.
A 10 cm long wire lies along y-axis. It carries a current of 1.0 A in positive y-direction. A magnetic field \(\vec{B}=(5 mT ) \hat{j}-(8 mT ) \hat{k}\) exists in the region. The force on the wire is :
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A 1 cm segment of a wire lying along x -axis carries current of 0.5 A along +x direction. A magnetic field \(\vec{B}=(0.4\mathrm{mT})\hat{j}+(0.6\mathrm{mT})\hat{k}\) is switched on, in the region. The force acting on the segment is
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A straight wire of length 1.0 m is placed along x -axis, in a region with magnetic field \(\vec{B}=(3\hat{i}+2\hat{j})T\). A current of 2.0 A flows in the wire along \(+x\) direction. The magnetic force acting on the wire is :
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A wire of length 4.4 m is bent round in the shape of a circular loop and carries a current of 1.0 A . The magnetic moment of the loop will be :
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A current carrying circular loop of magnetic moment \(\vec{M}\) is suspended in a vertical plane in an external magnetic field \(\vec{B}\) such that its plane is normal to \(\overrightarrow{ B }\). The work done in rotating this loop by \(45^{\circ}\) about an axis perpendicular to \(\vec{B}\) is closest to :
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Assertion (A) : Two long parallel wires, freely suspended and connected in series to a battery, move apart.
Reason (R) : Two wires carrying current in opposite directions repel each other.
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Assertion (A) : When radius of a circular loop carrying a steady current is doubled, its magnetic moment becomes four times.
Reason \((R)\) : The magnetic moment of a circular loop carrying a steady current is proportional to the area of the loop.
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Assertion (A) : A current carrying square loop made of a wire of length \(\mathrm{L}\) is placed in a magnetic field. It experiences a torque which is greater than the torque on a circular loop made of the same wire carrying the same current in the same magnetic field.
Reason \((R)\) : A square loop occupies more area than a circular loop, both made of wire of the same length.
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A particle of mass \(m\) and charge \(q\) moving with a uniform velocity \(\vec{v}=v_{0 x} \hat{i}+v_{0 y} \hat{j}\) enters a region with a magnetic field \(\vec{B}=B_0 \hat{j}\). After some time, an electric field \(\overrightarrow{ E }= E _0 \hat{ j }\) is also switched on in the region. The resulting path described by the particle will be :
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Two statements are given - one labelled Assertion (A) and the other labelled Reason \((R)\). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A) : A proton and an electron enter a uniform magnetic field \(\vec{B}\) with the same momentum \(\vec{p}\) such that \(\vec{p}\) is perpendicular to \(\vec{B}\). They describe circular paths of the same radius.
Reason (R): In a magnetic field, orbital radius r is equal to \(\frac{ p }{ qB }\).
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Assertion (A) and Reason (R) type questions. Two statements are given one labelled Assertion (A) and the other labelled Reason
(R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A) : An electron and a proton enter with the same momentum \(\vec{\mathrm{p}}\) in a magnetic field \(\vec{\mathrm{B}}\) such that \(\vec{\mathrm{p}}⊥\vec{\mathrm{B}}\). Then both describe a circular path of the same radius.
Reason (R) : The radius of the circular path described by the charged particle (charge \(q\), mass \(m\) ) moving in the magnetic field \(\vec{B}\) is given by \(r=\frac{mv}{qB}\).
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Assertion (A) : The deflection in a galvanometer is directly proportional to the current passing through it.
Reason (R) : The coil of a galvanometer is suspended in a uniform radial magnetic field.
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Two statements are given - one labelled Assertion (A) and the other labelled Reason \((R)\). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A) : Two long parallel wires, freely suspended and connected in series to a battery, move apart.
Reason ( \(R\) ): Two wires carrying current in opposite directions repel each other.
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A circular loop of radius r is carrying current I. The ratio of magnetic field at the centre of circular loop and at a distance r from the center of the loop on its axis is:
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Assertion (A) : The deflecting torque acting on a current carrying loop is zero when its plane is perpendicular to the direction of magnetic field.
Reason (R) : The deflecting torque acting on a loop of magnetic moment \(\vec{m}\) in a magnetic field \(\vec{B}\) is given by the dot product of \(\vec{m}\) and \(\vec{B}\).
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Assertion (A) : The energy of a charged particle moving in a magnetic field does not change.
Reason (R) : It is because the work done by the magnetic force on the charge moving in a magnetic field is zero.
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Two long parallel wires kept \(2 \mathrm{~m}\) apart carry \(3 \mathrm{~A}\) current each, in the same direction. The force per unit length on one wire due to the other is
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Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R).
Select the correct answer from the codes (A), (B), (C) and (D)as given below.
Assertion (A) : The torque acting on a current carrying coil is maximum when it is suspended in a radial magnetic field.
Reason (R) : The torque tends to rotate the coil on its own axis.
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