CBSE Questions for Class 12 Medical Physics Moving Charges And Magnetism Quiz 5 - MCQExams.com

A wire bent as shown in Figure carries a current $$I$$. Find the magnetic field at $$P$$ :

142968_8d65bdbd855f48aba48ebc74f6adcd64.png
  • $$\dfrac {\mu_0I}{4R}$$
  • $$\dfrac {3\mu_0I}{2R}$$
  • $$\dfrac {7\mu_0I}{8R}$$
  • $$\dfrac {\mu_0I}{8R}$$
The substance in which the resultant magnetic moment of individual atoms in zero
  • Para Magnetic Substance
  • Diamagnetic
  • Ferro Magnetic
  • None of these
According to Fleming's Left Hand Rule, the ....... points in the direction of the magnetic field.
  • Thumb
  • Forefinger
  • Second finger
  • Middle finger
A wire carrying current of $$10A$$ supports a wire of $$10cm$$ long and weighing $$1 g$$ vertically above it at a distance of $$1 cm$$. The current that is passing through the wire is :
  • $$490A$$
  • $$205A$$
  • $$408A$$
  • $$316A$$
A magnetic field $$4\times 10^{-3}\hat{k}T$$ exerts a force $$(4\hat{i}+3\hat{j})\times 10^{-10}N$$ on a particle having a charge $$10^{-9}$$C and going in the X-Y plane. The velocity of the particle is
  • $$-75\hat{i}+100\hat{j}$$
  • $$100\hat{i}+75\hat{j}$$
  • $$75\hat{i}+100\hat{j}$$
  • $$100\hat{i}-75\hat{j}$$
An $$\alpha $$ -particle describes a circular path of radius $$r$$ in a magnetic field $$B$$. The radius of the circular path described by the proton of same energy in the same magnetic field is :
  • $$\dfrac{r}{2}$$
  • $$r$$
  • $$\sqrt{2}r$$
  • $$2r$$
The magnetic induction at O due to a current in conductor shaped as shown in figure is:

23886_9a75644f52144a319a89b637cb8c5fd4.png
  • $$\dfrac{\mu _{0}i}{4\pi }\left [ \dfrac{3\pi }{2a}+\dfrac{\sqrt{2}}{b} \right ]$$
  • $$\dfrac{\mu _{0}i}{4\pi }\left [ \dfrac{3\pi }{4a}-\dfrac{\sqrt{2}}{b} \right ]$$
  • $$\dfrac{\mu _{0}i}{2\pi }\left [ \dfrac{3\pi }{4a}-\dfrac{1}{\sqrt{2}b} \right ]$$
  • $$\dfrac{\mu _{0}i}{2\pi }\left [ \dfrac{1}{a}+\dfrac{1}{b} \right ]$$
A charged particle with velocity $$\vec{v}=x\hat{i}+y\hat{j}$$ moves in a magnetic field $$\vec{B}=y\hat{i}+x\hat{j}$$. The magnitude of magnetic force acting on the particles F. Among the following the correct statement(s) is/are :
  • no force will act on particle, if $$ x =y$$
  • $$F\alpha (x^{2}-y^{2})$$ is x > y
  • the force will act along z-axis, if x > y
  • the force will act along y-axis, if y > x
In the given diagram, two long parallel wires carry equal currents in opposite direction. The magnetic field B at O (origin) is non-zero along:

23892_10c7737ef6194df0ad19a85e4cfe0ca0.png
  • x, y and z-axis
  • x-axis
  • y-axis
  • z-axis
Two long conductors, separated by a distance d carry currents $$ I_{1}$$ and  $$ I_{2}$$ in the same direction. They exert a force F on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3 times. The new value of the force between them is :
  • $$-\dfrac{2F}{3}$$
  • $$\dfrac{F}{3}$$
  • $$-2F$$
  • $$-\dfrac{F}{3}$$
A circular coil of 100 turns and effective diameter 20 cm carries a current of 0.5 A. It is to be turned in a magnetic field of $$B = 2.0 T$$ from a position in which the normal to the plane of the coil makes an angle $$\theta $$ equals to zero to one in which $$\theta $$ equals to $$180^o$$. The work required in this process is:
  • $$\pi \ J$$
  • $$2\pi\  J$$
  • $$4\pi\  J$$
  • $$8\pi\  J$$
A charge $$q(>0)$$ moves towards the centre of a circular loop of radius $$R$$ along its axis. The magnitude of B along the periphery of the loop is

24028.jpg
  • $$zero$$
  • $$\dfrac{\mu _{0}}{4\pi }\dfrac{qvR}{\sqrt{(R^{2}+x^{2})^{3}}}$$
  • $$\dfrac{qvR}{\sqrt{R^{2}+x^{2}}}$$
  • $$\dfrac{\mu _{0}}{4\pi }\dfrac{qvR}{\sqrt{R^{2}+x^{2}}}$$
A wire of length $$L$$ is shaped into a circle and then bent in such a way that the two semi-circles are perpendicular. The magnetic moment of the system when current $$I$$ flows through the system is :
  • $$\dfrac{\sqrt{2}iL^{2}}{8\pi }$$
  • $$\dfrac{\sqrt{3}iL^{2}}{4\pi }$$
  • $$\dfrac{iL^{2}}{4\pi }$$
  • $$\dfrac{iL^{2}}{2\pi }$$
The potential energy of a bar magnet of magnetic moment $$M$$ placed in a magnetic field of magnitude $$B$$ such that it makes an angle $$\theta$$ with the direction of $$B$$ is:
  • $$MB\sin {\theta}$$
  • $$-MB\cos {\theta}$$
  • $$MB(1-\cos {\theta})$$
  • $$MB(1+\cos {\theta})$$
A charged particle enters a magnetic field at right angles to the field. The field exists for a length equal to 1.5 times the radius of circular path of particle. The particle will be deviated from its path by :
  • $$90^{o}$$
  • $$sin^{-1}\left ( \dfrac{2}{3} \right )$$
  • $$30^{o}$$
  • $$180^{o}$$
A charged particle is projected in a magnetic field $$\vec{B}=(3\vec{i}+4\vec{j})\times 10^{-2}T$$ and the acceleration is found to be $$\vec{a}=(x\vec{i}+2\vec{j})m/s^{2}$$. The value of x is :
  • -8/3 $$m/s^{2}$$
  • 8/3 $$m/s^{2}$$
  • -4/3 $$m/s^{2}$$
  • 4/3 $$m/s^{2}$$
The magnetic moment of a circular coil of radius $$(r)$$, carrying a current $$(I)$$ and number of turns $$(n)$$ varies as
  • $$\dfrac{1}{r^2}$$
  • $$\dfrac{1}{r}$$
  • $$r$$
  • $$r^2$$
A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through $$60^0$$. The torque needed to maintain the needle in this position will be:
  • $$\sqrt{3}\mathrm{W}$$
  • $$W$$
  • $$\sqrt{3/2}\mathrm{W}$$
  • 2W
A current carrying loop is placed in a uniform magnetic field in four different orientations, I, II, III & IV, arrange them in the decreasing order of Potential Energy.


42955.jpg
  • $$|>|||>||>$$
  • $$|>||>|||>$$
  • $$|>|\mathrm{V}>||>$$ III
  • $$|||>|\mathrm{V}>|>$$ II
A rectangular coil of area A of N turns has a current I flowing in clockwise direction when looked at from above. The magnetic moment associated with it
  • Points upwards
  • Points vertically downwards
  • Is zero
  • Is directly proportional to $$A^2$$
A charged particle of specific charge $$\alpha $$  moves with a velocity $$\vec{v}=v_{0}\hat{i}$$ in a magnetic field $$\vec{B}=\frac{B_{0}}{\sqrt{2}}(\hat{j}+\hat{k})$$. Then : (specific charge $$=$$ charge per unit mass)
  • path of the particle is a helix
  • path of the particle is a circle
  • distance moved by particle intime $$t=\dfrac{\pi}{B_{0}\alpha } \ is \ \dfrac{\pi v_{0}}{B_{0}\alpha }$$
  • velocity of particle after time $$t=\dfrac{\pi}{B_{0}\alpha }is\left ( \dfrac{v_{0}}{2}\hat{i} +\dfrac{v_{0}}{2}\hat{j}\right )$$
A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is in which direction?
  • towards south
  • towards east
  • downward
  • upward
Energy associated with an electric field is analogous to _______ whereas the energy associated with the magnetic field is analogous to ________. 
  • kinetic energy, potential energy
  • potential energy, potential energy
  • potential energy, kinetic energy
  • kinetic energy, kinetic energy
A conductor of length $$l$$ carrying current $$i$$ is placed perpendicular to magnetic field of induction $$B$$. The force experienced by it is :
  • $$i lB$$
  • $$\dfrac{iB}{l}$$
  • $$\dfrac{il}{B}$$
  • $$\dfrac{lB}{i}$$
An electron and a proton move in a uniform magnetic field with same speed $$20 \ m/s$$ perpendicular to the magnetic field ($$1 T$$). What are the forces they will experience ?
  • $$0 N, 0 N$$
  • $$32 \times 10^{-19} N, 32 \times 10^{-19} N$$
  • $$-32 \times 10^{-19} N, 32 \times 10^{-19} N$$
  • $$-32 \times 10^{-18} N, 32 \times 10^{-18} N$$
What happens to energy when a charged particle moving in a magnetic field although a magnetic force is acting on it ?
  • remains constant
  • increases
  • decreases
  • none of these.
Product of pole strength of a magnet and magnetic length is called
  • Magnetic Strength
  • Pole Strength
  • Magnetic Movement
  • None of these
A circular coil of $$16$$ turns and radius $$10$$ cm carrying a current of $$0.75 A$$ rests with its plane normal to an external field of magnitude $$5.0 \times 10^{-2}T$$. The coil is free to turn about an axis in its plane perpendicular to the filed direction. When the coil is turned slightly and released, it oscillates about its stable equilibrium with a frequency of $$2.0/s$$. What is the moment of inertia of the coil about its axis of rotation?
  • $$1.2 \times 10^{4} g-cm^2$$
  • $$3\times 10^{4} kg-m^2$$
  • $$0.3 \times 10^{4} kg-m^2$$
  • $$1.2 \times 10^{4} kg-m^2$$
A particle of mass $$M$$ and charge $$Q$$ moving with a velocity $$\overrightarrow{v}$$ described a circular path of radius $$R$$ when subjected to a uniform transverse magnetic field of induction $$B$$. The work done by the field when the particle completes one full circle is
  • $$zero$$
  • $$BQ2\pi R$$
  • $$BQv(2\pi R)$$
  • $$\left (\dfrac {Mv^2}{R}\right )(2\pi R)$$
A wire bent as shown in Fig is oriented along yz plane. Find the magnetic field at P and $$P_1$$.

142974_6201ff3542794344a46e18801dd6cf0e.png
  • $$\frac {\mu_0I}{4a}, \frac {\mu_0I}{2\pi x}$$
  • $$\frac {\mu_0I}{4a}, \frac {\mu_0I}{2\pi (x^2+a^2)}$$
  • $$\frac {\mu_0I}{4a}, \frac {\mu_0I}{2\pi a(x^2+a^2)}$$
  • none of these
Two thin long, parallel wires separated by a distance $$d$$ carry a current $$i$$ each in the same direction. They will
  • repel each other with a force per unit length of  $$\dfrac {\mu_0i^2}{2\pi d}$$
  • attract each other with a force per unit length of $$\dfrac {\mu_0i^2}{2\pi d}$$
  • repel each other with a force per unit length of $$\dfrac {\mu_0i^2}{2\pi d^2}$$
  • attract each other with a force per unit length of $$\dfrac {\mu_0i^2}{2\pi d^2}$$
Two particles X and Y having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths or radii $$R_1$$ and $$R_2$$ respectively. The ratio of mass of X to that of  Y is equal to :
  • $$\left( \dfrac { { R }_{ 1 } }{ { R }_{ 2 } } \right) ^{ 2 }$$
  • $$\left( \dfrac { { R }_{ 1 } }{ { R }_{ 2 } } \right)$$
  • $$\left( \dfrac { { R }_{ 1 } }{ { R }_{ 2 } } \right) ^{ 1/2 }$$
  • $$\dfrac { { R }_{ 2 } }{ { R }_{ 1 } } $$
A closely wound solenoid of $$800$$ turns and area of cross-section $$2.5 \times 10^{-4} m^2$$ carries a current of $$3.0 A$$. Explain the sense in which the solenoid acts line a bar magnet. What is its associated magnetic moment?
  • $$6 J/T$$
  • $$0.9 J/T$$
  • $$9 J/T$$
  • $$0.6 J/T$$
An $$\alpha$$ -particles enters at the middle as shown in Fig. with $$10^5 ms^{-1}$$. In which direction will it bend?

142869.png
  • towards 1 A wire
  • towards 3 A wire
  • upwards the plane of wires
  • downwards the plane of wires
A hollow tube is carrying an electric current along its length distributed uniformly over its surface. The magnetic field :
  • increases linearly from the axis to the surface
  • is constant inside the tube
  • is zero at the axis
  • is zero just outside the tube
A straight conductor carries a current. Assume that all free electrons in the conductor move with the same drift velocity v. A and B are two observers on a straight line XY parallel to the conductor. A is stationary. B moves along XY with a velocity v in the direction of the free electrons.
  • A and B observe the same magnetic field
  • A observes a magnetic field, B does not
  • A and B observe magnetic fields of the same magnitude but opposite directions
  • A and B do not observe any electric field
The magnetic field at the origin due to a current element $$i.\vec {dl}$$ placed at a position $$\vec r$$ is
  • $$\dfrac {\mu_0i}{4\pi} \dfrac {\vec {dl}\times \vec r}{r^3}$$
  • $$\dfrac {\mu_0i}{4\pi} \dfrac {\vec r\times \vec {dl}}{r^3}$$
  • $$-\dfrac {\mu_0i}{4\pi} \dfrac {\vec r\times \vec {dl}}{r^3}$$
  • $$-\dfrac {\mu_0i}{4\pi} \dfrac {\vec {dl}\times \vec r}{r^3}$$
An observer A and a charge Q are fixed in a stationary frame $$F_1$$. an observer B is fixed in a frame $$F_2$$, which is moving with respect to $$F_1$$ :

143076_5de2281f03d84390bebdf733ebc068ff.png
  • both A and B will observe electric fields
  • both A and B will observe magnetic fields
  • neither A nor B will observe magnetic fields
  • B will observe a magnetic field, but A will not
In a coaxial, straight cable, the central conductor and the outer conductor carry equal currents in opposite directions. The magnetic field is zero :
  • outside the cable
  • inside the inner conductor
  • inside the outer conductor
  • in between the two conductors
A long straight conductor, carrying a current $$i$$, is bent to form an almost complete circular loop of radius $$r$$ as shown. The magnetic field at the centre of the loop :

143202_05681380fdd243ab8076eae339535967.png
  • has magnitude $$\dfrac {\mu_0i}{r}\left (1-\dfrac {1}{\pi}\right )$$
  • has magnitude $$\dfrac {\mu_0i}{r}\left (1+\dfrac {1}{\pi}\right )$$
  • has magnitude $$\dfrac {\mu_0i}{2r}\left (1-\dfrac {1}{\pi}\right )$$
  • has magnitude $$\dfrac {\mu_0i}{2r}\left (1+\dfrac {1}{\pi}\right )$$
The force $$F$$ acting on charge $$q$$ moving with velocity $$v$$ perpendicular to magnetic field $$B$$ is:
  • $$F = qvB$$
  • $$F = \dfrac {qv}{B}$$
  • $$F = \dfrac {qB}{v}$$
  • $$F = \dfrac {Bv}{q}$$
A steady electric current is flowing through a cylindrical conductor
  • the electric field at the axis of the conductor is zero
  • the magnetic field at the axis of the conductor is zero
  • the electric field in the vicinity of the conductor is zero
  • the magnetic field in the vicinity of the conductor is zero
A fiat circular coil, carrying a current, has a magnetic moment $$\mu$$
  • $$\mu$$ has only magnitude; it does not have direction
  • the direction of $$\mu$$ is along the normal to the plane of the coil
  • the direction of $$\mu$$ depends on the direction of the current flow
  • the direction of $$\mu$$ does not change if the current in the coil is reversed
A long straight wire of radius R carries a current distributed uniformly over its cross-section. The magnitude of the magnetic field is
  • maximum at the axis of the wire
  • minimum at the axis of the wire
  • maximum at the surface of the wire
  • minimum at the surface of the wire
A current i is flowing in a conductor as shown in the figure. The magnetic induction at point O will be :

143230_5b905670e48c450299420036ff392881.png
  • zero
  • $$\mu_0i/r$$
  • $$2\mu_0i/r$$
  • $$\mu_0i/4r$$
The phenomenon of production of magnetic field on passing an electric current in a straight conducting wire is based on the law of
  • Faraday
  • Coulomb
  • Ampere
  • Oersted
Two parallel straight conductors, in which current is flowing in the same direction, attract each other. The cause of it is
  • magnetic force between the two
  • electric force between the two
  • potential difference between the two
  • mutual induction between the two
The work done by a normal magnetic field in revolving a charged particle q in a circular path will be
  • zero
  • $$MB (1-cos\theta)$$
  • $$MB$$
  • $$-MB$$
A charged particle with charge $$q$$ is moving in a uniform magnetic field. If this particle makes any angle with the magnetic field then its path will be :
  • circular
  • straight line
  • helical
  • parabolic
The distance between two thin long straight parallel conducting wires is $$b$$. On passing the same current $$i$$ in them, the force per unit length between them will be
  • $$\dfrac {\mu_0i}{2\pi b}$$
  • $$\dfrac {\mu_0i^2}{2\pi}$$
  • $$\dfrac {\mu_0i^2}{2\pi b}$$
  • zero
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