CBSE Questions for Class 12 Medical Physics Moving Charges And Magnetism Quiz 3 - MCQExams.com

A charged particle experiences magnetic force in the presence of magnetic field. Which of the following statement is correct?
  • The particle is moving and magnetic field is perpendicular to the velocity.
  • The particle is moving and magnetic field is parallel to velocity.
  • The particle is stationary and magnetic field is perpendicular.
  • The particle is stationary and magnetic field is parallel.
Quantity that is not affected by magnetic field is:
  • Moving charge
  • Change in magnetic flux
  • Current flowing in conductor
  • Stationary charge
State whether True or False :
Lenz's law defines the polarity of the induced voltage.
  • True
  • False
Identify the wrong statement.
  • Current loop is equivalent to a magnetic dipole
  • Magnetic dipole moment of a planar loop of area $$A$$ carrying current $$l$$ is $$l^{2}A$$
  • Particles like proton, electron carry an intrinsic magnetic moment
  • The current loop (magnetic moment $$m$$) placed in a uniform magnetic field, $$B$$ experiences a torque $$\tau = m\times B$$
  • Ampere's circuit law is not independent of Biot Savart's law
A charged particle is moving along a magnetic field line. The magnetic force on the particle is
  • Along its velocity
  • Opposite to its velocity
  • Perpendicular to its velocity
  • Zero
Choose the correct alternative which matches second and third column with first column:
Column IColumn IIColumn III
(I) Magnetic field is produced 
near current carrying conductor		(A) Right hand
thumb rule		(a) Micheal Faraday
(II) Electric current is generated
in a conductor moving in a 
magnetic field.		(B) Fleming's right
hand rule		(b) Hans Oersted
  • (I)-(B)-(a),(II)-(B)-(b)
  • (I)-(A)-(b),(II)-(B)-(b)
  • (I)-(B)-(b),(II)-(A)-(a)
  • (I)-(A)-(b),(II)-(B)-(a)
A uniform magnetic field exists in the plane of paper pointing from left to right as shown in figure. In the field, an electron and a proton move as shown. The electron and the proton experiences:

764054_d93725abd14148fcbc5ae5340fc30f15.JPG
  • Forces both pointing into the plane of paper
  • Forces both pointing out of the plane of paper
  • Forces pointing into the plane of paper and out of the plane of paper respectively
  • Forces pointing opposite and along the direction of the uniform magnetic field respectively.
A bar magnet of magnetic moment $$M$$ is bent to form a semicircle. What is the magnetic moment of the bent magnet?
  • $$\cfrac{M}{\pi}$$
  • $$\cfrac{2M}{\pi}$$
  • $$\cfrac{M\pi}{2}$$
  • $$M$$
An eleclron is travelling horizontallty towards east. A magnetic field in vertically downward (inside the plane of paper) direction exerts a force on the electron along
  • East
  • West
  • North
  • South
When a charged particle moves in a magnetic field its kinetic energy __________.
  • Remains constant
  • Increases
  • Can decrease
  • Become zero
A electron with kinetic energy $$k$$ enters a region (i) uniform magnetic field (ii) non-uniform magnetic field and comes out with kinetic energy $$k_1$$ and $$k_2$$ respectively. What is relation between $$k_1, k_2$$ and $$k$$?
  • $$K_1 > K_2 > K$$
  • $$K_1 = K_2 > K$$
  • $$K_1 = K_2 = K$$
  • $$K_1 < K_2 < K$$
The gyromagnetic ratio of an electron $$=$$__________ specific charge of an electron.
  • $$1$$
  • $$2$$
  • $$1/2$$
  • $$4$$

The work done in turning a magnet of magnetic moment $$M$$ by an angle of $$90^{o}$$ from the meridian is $$n$$ times the corresponding work done to turn it through an angle of $$60^{o}$$ from the meridian, where $$n$$ is given by :
  • $$\dfrac{1}{2}$$
  • $$2$$
  • $$\dfrac{1}{4}$$
  • $$1$$
The distance between the wires of electric mains is 12cm. These wires exprience 4 mgwt per unit length. The value of current flowing in each wire will be if they carry current in same direction
  • 4.85A
  • zero
  • $$4.85\times 10^{-2}A$$
  • $$85\times 10^{-4}A$$

A magnet of moment $$4 \ Am^{2}$$ is suspended in a uniform magnetic field of induction $$5\times 10^{-4} \ T$$ with its axis at right angles. When the magnet is released from it's position, the kinetic energy that it gains in passing to the stable equilibrium position is :
  • $$10^{-4}$$ J
  • $$10^{-3}$$ J
  • $$2\times 10^{-3}J$$
  • $$5\times 10^{-4}J$$
The work done in rotating the magnet from the direction of uniform field to the opposite direction to the field is $$W$$. The work done in rotating the magnet from the field direction to half the maximum couple position is :
  • $$2\ W$$
  • $$\dfrac{\sqrt{3}W}{2}$$
  • $$\dfrac{W}{4}(2-\sqrt{3})$$
  • $$\dfrac{W}{4}(1-\sqrt{3})$$

A magnet of moment $$1.2\ Am^{2}$$ is kept suspended in a magnetic field of induction $$2\times 10^{-6}$$. The work done in rotating it through 120$$^{o}$$ is:
  • $$2.4\times 10^{-6}J$$
  • $$4.8\times 10^{-6}J$$
  • $$1.2\times 10^{-6}J$$
  • $$3.6\times 10^{-6}J$$
An electron enters a magnetic field with a speed of $$10^{8} cm/s$$. The particle experiences a force due to the magnetic field and the speed of the electron
  • will decrease
  • will increase
  • will remain constant
  • may in crease or decrease

Assertion: When radius of a circular wire carrying current is doubled, its magnetic moment becomes four times 

Reason: Magnetic moment is directly proportional to area of the loop
  • Both A and R are true and R is the correct explanation of A.
  • Both A and R are true and R is not correct explanation of A.
  • A is true, but R is false
  • A is false, but R is true

The magnetic moment of a bar magnet is 0.256 amp.m$$^{2}$$. Its pole strength is 400 milli amp. m. It is cut into two equal pieces and these two pieces are arranged at right angles to each other with their unlike poles in contact (or like poles in contact). The resultant magnetic moment of the system is
  • $$\sqrt{2}\times 256\times 10^{-3}Am^{2}$$
  • $$250\times 10^{-3}Am^{2}$$
  • $$\dfrac{256}{\sqrt{2}}\times 10^{-3}Am^{2}$$
  • $$\dfrac{128}{\sqrt{2}}\times 10^{-3}Am^{2}$$
An electron of mass m is accelerated through a potential difference of V and then it enters a magnetic field of induction B normal to the lines of force. Then the radius of the circular path is
  • $$\sqrt{\dfrac{2eV}{m}}$$
  • $$\sqrt{\dfrac{2Vm}{eB^{2}}}$$
  • $$\sqrt{\dfrac{2Vm}{eB}}$$
  • $$\sqrt{\dfrac{2Vm}{e^{2}B}}$$
A bar magnet of magnetic moment 3.0 A-m$$^{2}$$ is free to rotate about a vertical axis passing through its centre. The magnet is released from rest from east - west position. Then the kinetic energy of the magnet as it takes North- South position is :
(horizontal component of earths magnetic field is 25$$\mu $$T)
  • 25 $$\mu $$ J
  • 75 $$\mu $$J
  • 100$$\mu $$ J
  • 12.5 $$\mu $$ J

A magnet is in stable equilibrium in a uniform magnetic field. It is deflected by $$60^{o}$$ and the workdone is equal to $$W$$. In deflecting the magnet further by $$30^{o}$$, Work done is:
  • $$\dfrac{W\sqrt{3}}{2}$$
  • $$\dfrac{W}{4}$$
  • $$\dfrac{W}{2}$$
  • $$W$$
A magnet of magnetic moment $$M$$ is rotated through 360$$^\circ$$ in a magnetic field $$H$$. Work done will be
  • $$0$$
  • $$2\ MH$$
  • $$MH$$
  • $$\pi MH$$
When a charged particle moves through a magnetic field, the quantity which is not affected in the magnetic field is:
  • particle velocity
  • particle acceleration
  • linear momentum of the particle
  • kinetic energy of the particle
The force felt by an electron on entering into a magnetic field is independent of its
  • Charge
  • Strength of the field
  • Mass
  • Direction of its velocity
You are sitting in a room in which uniform magnetic field is present in vertically downward direction. When an electron is projected in horizontal direction, it will be moving in circular path with constant speed
  • clockwise in vertical plane
  • clockwise in horizontal plane
  • anticlockwise in vertical plane
  • anticlockwise in horizontal plane
The magnetic field  $$\overline{dB}$$ due to a small current element dl at a distance $$\vec{r}$$ and carrying current ‘i’ is
  • $$\overline{dB}=\dfrac{\mu _{0}}{4\pi }i\left ( \dfrac{\overline{dl}\times \bar{r}}{r} \right )$$
  • $$\overline{dB}=\dfrac{\mu _{0}}{4\pi }i^{2}\left ( \dfrac{\overline{dl}\times \bar{r}}{r^{2}} \right )$$
  • $$\overline{dB}=\dfrac{\mu _{0}}{4\pi }i^{2}\left ( \dfrac{\overline{dl}\times \bar{r}}{r} \right )$$
  • $$\overline{dB}=\dfrac{\mu _{0}}{4\pi }i\left ( \dfrac{\overline{dl}\times \bar{r}}{r^{3}} \right )$$
For a given distance from a current element, the magnetic induction is maximum at an angle measured with respect to axis of the current. The angle is :
  • $$\dfrac{3\pi}{ 4}$$
  • $$\dfrac{\pi }{4}$$
  • $$\dfrac{\pi} {2}$$
  • $$2\pi $$
An electron and a proton are injected into a uniform magnetic field at right angle to its direction with the same momentum. Then
  • electrons path isless curved than protons path
  • protons path will be less curved than electrons

    path
  • the paths of both will be equally curved
  • both the trajectories will be straight
Magnetic field at a point on the line of current carrying conductor is
  • maximum
  • infinity
  • zero
  • finite value
A cathode ray beam is bent into an arc of a circle of radius $$0.02 m$$ by a field of magnetic induction $$4.55 mT$$. The velocity of electrons is:
(Given $$e=1.6\times 10^{-19}c$$ and $$m=9.1\times 10^{-31}kg$$)
  • $$2\times 10^{7}m/s$$
  • $$3\times 10^{7}m/s$$
  • $$1.6\times 10^{7}m/s$$
  • $$3.2\times 10^{7}m/s$$
The magnetic field due to a current element is independent of :
  • current through it
  • distance from it
  • its length
  • nature of meterial
A $$\beta -$$ particle enters a magnetic field making an angle of $$45^{o}$$ with the field lines. The path of the particle is
  • circular
  • elliptical
  • spiral
  • a straight line
An electron and a proton enter a magnetic field with equal velocities. The particle that experiences more force is
  • electron
  • proton
  • both experience same force
  • it cannot be predicted.
A magnetic field exerts no force on
  • a stream of electrons
  • a stream on protons
  • unmagnetised piece of iron
  • stationary charge.
A charged particle enters into a uniform magnetic field the parameter that remains constant is
  • velocity
  • momentum
  • kinetic energy
  • angular velocity
A charged particle is moving with velocity $$v$$ in a magnetic field of induction $$B$$. The force on the particle will be maximum when
  • $$v$$ and $$B$$ are in the same direction
  • $$v$$ and $$B$$ are in Opposite direction
  • $$v$$ and $$B$$ are perpendicular
  • $$v$$ and $$B$$ are at an angle of $$45^{o}$$
A charge moving with velocity $$v$$ in $$X-$$ direction is subjected to a field of magnetic induction in the negative $$X$$ direction. As a result the charge will :
  • remain unaffected
  • start moving in a circular path in $$Y-Z$$ plane
  • retard along $$X-$$axis
  • move along a helical path around $$X -$$ axis
The mono energetic beams of electrons moving along +y direction enter a region of uniform electric and magnetic fields. If the beam goes straight through these simultaneously, then field B and E are directed possibly along
  • -y axis and -z axis
  • +z axis and -x axis
  • + x axis and - x axis
  • -x axis and -y axis
A free charged particle moves through a magnetic field. The particle may undergo a change in
  • speed
  • energy
  • direction of motion
  • magnitude of the velocity
A charged particle moving in a magnetic field experiences a resultant force
  • in the direction opposite to that of the field.
  • in the direction opposite to that of its velocity
  • in the direction perpendicular to both field &

    its velocity
  • in the direction parallel to the field
A proton and an electron enter a region with equal speed in which a magnetic field is suddenly switched on. The force experienced by them are
  • equal and opposite
  • different in magnitude but same in direction
  • in the ratio of 1840
  • same in magnitude and direction
When a charged particle moves in a uniform magnetic field
  • it gains energy from the field
  • it loses energy to the field
  • it neither gains nor changes energy and momentum
  • momentum changes but not energy
A proton enters a magnetic field with a velocity of $$2.5\times 10^{7}ms^{-1}$$ making an angle $$30^{0}$$ with the magnetic field. The force on the proton is $$(B=25T)$$
  • $$1.25\times 10^{-11}N$$
  • $$2.5\times 10^{-11}N$$
  • $$5.0\times 10^{-11}N$$
  • $$7.5\times 10^{-11}N$$
A particle of mass $$M$$ and charge $$Q$$ moving with velocity $$\vec{v}$$ describes a circular path of radius $$R$$ when subjected to a uniform transverse magnetic field of induction $$\vec{B}$$. The work done by the field when the particle completes one full circle is 
  • $$MV^{2}R^2 $$
  • $$0$$
  • $$VBQR$$
  • $$2\pi VBQR$$
A current of one ampere is passed through a straight wire of length 2 metre. The magnetic field at a point in air at a distance of 3 m from one end of the wire but lying on the axis of the wire will be:
  • $$\mu _{0}/2\pi $$
  • $$\mu _{0}/4\pi $$
  • $$\mu _{0}/8\pi $$
  • Zero
Singly ionized helium(x), ionized deuteron(y), alpha(z) particles are projected into a uniform magnetic field $$3 \times 10^{-4}$$ Tesla with velocities $$10^{5} ms^{-1}$$, $$0.4 \times 10^{4} ms^{-1}$$ and $$2 \times 10^{3} ms^{-1}$$ respectively. The correct relation between the ratio of the angular momentum to the magnetic moment of the particles is :
  • $$x>y= z$$
  • $$x < y < z$$
  • $$x< z < y$$
  • $$z > x > y$$
A proton is rotating along a circular path with kinetic energy K in a uniform magnetic field B.If the magnetic field is made four times, the kinetic energy of rotation of proton is
  • 16K
  • 8K
  • 4K
  • K
A particle of mass $$0.6$$ $$g$$ and having a charge of $$25$$ $$nC$$ is moving horizontally with a uniform velocity $$1.2 \times10^{4}$$ $$m/s$$ in a uniform magnetic field, then the value of the magnetic induction is (Take $$g=10 \ m/s^2$$)
  • $$zero$$
  • $$10  T$$
  • $$20  T$$
  • $$200  T$$
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