CBSE Questions for Class 12 Medical Physics Moving Charges And Magnetism Quiz 7 - MCQExams.com

Two equal electric currents are flowing perpendicular to each other as shown in figure. AB and CD are perpendicular to each other and symmetrically placed with respect to the currents. Where do we expect the resultant magnetic field to be zero?
167420.png
  • on AB
  • on CD
  • on both AB & CD
  • on both OD & BO
Two long conductors, separated by a distance d carry current $$I_1$$ 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 3d. The new value of the force between them is
  • $$- \displaystyle \frac{2F}{3}$$
  • $$\displaystyle \frac{F}{3}$$
  • -2 F
  • $$- \displaystyle \frac{F}{3}$$
A particle of charge  $$q$$ and mass  $$m$$  moves in a circular orbit of radius $$r$$  with angular speed $$\omega$$. The ratio of the magnitude of its magnetic moment to that of its angular momentum depends on
  • $$\omega$$ and $$q$$
  • $$\omega,\ q$$ and $$m$$
  • $$q$$ and $$m$$
  • $$\omega$$ and $$m$$
Two thin long parallel wires separated by a distance $$b$$  are carrying a current $$I$$ ampere each. The magnitude of the force per unit length exerted by one wire on the other is
  • $$\dfrac {\mu_0I^2}{b^2}$$
  • $$\dfrac {\mu_0I^2}{2\pi b}$$
  • $$\dfrac {\mu_0I}{2\pi b}$$
  • $$\dfrac {\mu_0I}{2\pi b^2}$$
Current $$i$$ is flowing in a coil of area $$A\ \&$$ number of turns $$N,$$ then magnetic moment of the coil is $$M$$ is equal to
  • $$NiA$$
  • $$\dfrac{Ni}{A}$$
  • $$\dfrac{Ni}{\sqrt{A}}$$
  • $$N^2Ai$$
A current loop consists of two identical semicircular parts each of radius R, one lying in the x-y plane and the other in x-z plane. If the current in the loop is i., the resultant magnetic field due to the two semicircular parts at their common centre is
  • $$\displaystyle \frac{\mu_0 i}{\sqrt{2} R}$$
  • $$\displaystyle \frac{\mu_0 i}{ 2 \sqrt{2} R}$$
  • $$\displaystyle \frac{\mu_0 i}{2 R}$$
  • $$\displaystyle \frac{\mu_0 i}{4 R}$$
A loop carrying current $$I$$ lies in the $$x-y$$  plane as shown in figure. The unit vector $$\hat{k}$$ is coming out of the plane of the paper. The magnetic moment of the current loop is

167770.png
  • $$a^2I\hat{k}$$
  • $$\left (\dfrac {\pi}{2}+1\right)a^2I\hat{k}$$
  • $$-\left (\dfrac {\pi}{2}+1\right)a^2I\hat{k}$$
  • $$(2\pi +1)a^2I\hat{k}$$
An electron travelling with a speed u along the positive x-axis enters into a region of magnetic field where $$B=-B_0 \hat k(x > 0)$$. It comes out of the region with speed v. Then

167754_ffc764c24e8247d185ae14f89dc695fd.png
  • $$v=u$$ at y > 0
  • $$v=u$$ at y < 0
  • $$v > u$$ at y > 0
  • $$v > u$$ at y < 0
A charge $$q=-4\mu C$$ has an instantaneous velocity $$\vec{v}=(2\hat{i} -3\hat{j}+\hat{k})\times {10}^{6}m/s$$ in a uniform magnetic field $$\vec{B}=(2\hat{i} +5\hat{j}-3\hat{k})\times {10}^{-2}T$$.What is the force on the charge?
  • $$(-0.16\hat{i}-0.32\hat{j}-0.64\hat{k})N$$
  • $$(-0.16\hat{i}-0.12\hat{j}-0.44\hat{k})N$$
  • $$(-0.16\hat{i}-0.82\hat{j}-0.44\hat{k})N$$
  • $$(-0.12\hat{i}-0.12\hat{j}-0.64\hat{k})N$$
A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moment $$\mu$$ is given by
  • qvR$$^2$$
  • qvR$$^2$$/2
  • qvR
  • qvR/2
If an electron describes half a revolution in a circle of radius r in a magnetic field B, the energy acquired by it is
  • zero
  • $$\displaystyle \frac{1}{2} mv^2$$
  • $$\displaystyle \frac{1}{4} mv^2$$
  • $$\mu_r \times Bev$$
Through two parallel wires A and B, 10A and 2A of currents are passed respectively in opposite directions. If the wire A is infinitely long and the length of the wire B is 2m, then force on the conductor B, which is situated at 10 cm distance from A, will be
  • $$8 \times 10^{-7} N$$
  • $$8 \times 10^{-5} N$$
  • $$4 \times 10^{-7} N$$
  • $$4 \times 10^{-5} N$$
State condition when magnitude of force on a current carrying conductor placed in a magnetic field is zero.
  • When current in conductor is normal to the direction of magnetic field
  • When current in conductor is in the direction of magnetic field
  • When current in conductor is acute angled to the direction of magnetic field
  • When current in conductor is obtuse angled to the direction of magnetic field
How will the direction of force be changed, if the current is reversed in the conductor placed in a magnetic field ?
  • No direction.
  • Direction of force is reversed.
  • Direction of force remains same.
  • cant say
A deutron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 m, in a plane perpendicular to magnetic field $$\vec B$$. The kinetic energy of a proton that discribes a circular orbit of radius 0.5 m in the same plane with the same magnetic field $$\vec B$$ is
  • 200 keV
  • 50 keV
  • 100 keV
  • 25 keV
A closed curve encircles several conductors.The line integral $$\int{\vec{B}\cdot d\vec{l}}$$ around this curve is $$3.83\times {10}^{-7} T-m$$. What is the net current in the conductors?
  • $$0.1A$$
  • $$0.2A$$
  • $$0.3A$$
  • $$0.4A$$
If the acceleration and velocity of a charged particle moving in a constant magnetic region is given by $$\vec{a}={a}_{1}\hat{i}+{a}_{2}\hat{k},\vec{v}={b}-{1}\hat{i}+{b}_{2}\hat{k}$$.[$${a}_{1},{a}_{2},{b}_{1}$$ and $${b}_{2}$$ are constants],then choose the wrong statement
  • Magnetic field may be along y-axis
  • $${a}_{1}{b}_{1}+{a}_{2}{b}_{2}=0$$
  • Magnetic field is along x-axis
  • Kinetic energy of particle is always constant
A short bar magnet of magnetic moment $$0.4 J T^{1}$$ is placed in a uniform magnetic field of 0.16 T. The magnet is in stable equilibrium when the potential energy is
  • 0.064 J
  • -0.064 J
  • zero
  • 0.082 J
The figure shows the cross-section of two long coaxial tubes carrying equal currents $$I$$ in opposite directions. If $${B}_{1}$$ and $${B}_{2}$$ are magnetic fields at point 1 and 2, as shown in figure then
225043.png
  • $${B}_{1}\neq 0;{B}_{2}=0$$
  • $${B}_{1}=0;{B}_{2}=0$$
  • $${B}_{1}\neq 0;{B}_{2}\neq 0$$
  • $${B}_{1}=0;{B}_{2}\neq 0$$
A magnetic field cannot exert any force on a :
  • Moving magnet
  • Stationary magnet
  • Moving charge
  • Stationary charge
The acceleration of an electron at a certain moment in a magnetic field $$\vec{B}=2\hat{i}+3\hat{j}+4\hat{k}$$ is $$\vec{a}=x\hat{i}+\hat{j}-\hat{k}$$.The value of x is
  • 0.5
  • 1
  • 2.5
  • 1.5
A wire is placed between the poles of two fixed bar magnets as shown. A small current in the wire is into the plane of the paper. The direction of the magnetic force on the wire is
303646.png
  • $$\uparrow$$
  • $$\downarrow$$
  • $$\rightarrow$$
  • $$\leftarrow$$
  • $$\odot$$ out of the plane of the paper.
Two long parallel wires are at a distance of 1m. If both of them carry one ampere of current in same direction, then the force of attraction on unit length of the wires will be
  • $$2\times 10^{-7}N/m$$
  • $$4\times 10^{-7}N/m$$
  • $$8\times 10^{-7}N/m$$
  • $$10^{-7}N/m$$
If the particle were negatively charged then what will be the magnitude of force on the charged particle?
  • $$23.04\times {10}^{-6}N$$
  • $$230.4\times {10}^{-5}N$$
  • zero
  • None of these
The equation of line on which magnetic field is zero due to system of two perpendicular infinitely long current carrying straight wires, is
293612.PNG
  • $$x=y$$
  • $$x=2y$$
  • $$x=3y$$
  • $$3x=y$$
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection.
  • True
  • False
  • Ambiguous
  • Data insufficient
A charged particle moves through a magnetic field in a direction perpendicular to it. Then the
  • speed of the particle remains unchanged
  • direction of the particle remains unchanged
  • acceleration remains unchanged
  • velocity remains unchanged
When a charged particle moving with velocity $$\vec V$$ is subjected to a magnetic field of induction $$\vec B$$, the force on it is non-zero. This implies the
  • Angle between $$\vec V$$ and $$\vec B$$ is necessary $$90^o$$
  • Angle between $$\vec V$$ and $$\vec B$$ can have a value other than $$90^o$$
  • Angle between $$\vec V$$ and $$\vec B$$ can have a value other than zero and $$180^o$$
  • Angle between $$\vec V$$ and $$\vec B$$ is either zero or $$180^o$$
An electron has a circular path of radius $$0.01 m$$ in a perpendicular magnetic induction $$10^{-3} T$$. The speed of the electron is nearly
  • $$7.04 \times 10^{6}\ {ms}^{-1}$$
  • $$1.76 \times 10^{6}\ {ms}^{-1}$$
  • $$3.52 \times 10^{6}\ {ms}^{-1}$$
  • $$1.76 \times 10^{4}\ {ms}^{-1}$$
A proton is moving with velocity $${10}^{4}m/s$$ parallel to the magentic field of intensity 5 tesla.The force on the proton is
  • $$8\times {10}^{-15}N$$
  • $${10}^{4}N$$
  • $$1.6\times {10}^{-19}N$$
  • Zero
In the given figure, what is the magnetic field at the point 'O' ?
334187_136fe87b1acf4eec9dfb93308c41c2ba.png
  • $$\displaystyle \frac{\mu _0I}{4\pi r}\, +\, \frac{\mu _0I}{2\pi r}$$
  • $$\displaystyle \frac{\mu _0I}{ 4 \pi r}$$
  • $$\displaystyle \frac{\mu _0I}{4r }\, +\, \frac{\mu _0I}{4\pi r}$$
  • $$\displaystyle \frac{\mu _0I}{4r }\, -\, \frac{\mu _0I}{4\pi r}$$
Consider a wire carrying a steady current placed in a uniform magnetic field B perpendicular to its length Consider the charges inside the wire It is known that magnetic forces do no work This implies that
  • motion of charges inside the conductor is unaffected by B since they do not absorb energy
  • some-charges inside the wire move to the surface as a result of B
  • If the wire moves under the influence of B no work is done by the force
  • it the wire moves under the influence of B no work is done by the magnetic forces on the ions assumed fixed the wire
Two charges of same magnitude move in two circlesof radii $$R_1 = R$$ and $$R_2 = 2R$$ in a region of constant uniform magnetic field $$B_0$$. The work $$W_1$$, and $$W_2$$ done by the magnetic field in the Two cases, respectively are such that:
  • $$W_1 = W_2 = 0$$
  • $$W_1 > W_2$$
  • $$W_1 = W_2 \neq 0$$
  • $$W_1 < W_2$$
Two charges of same magnitude move in two circles of radii $$R_1\,  =\, R\, and\,  R_2\, =\, 2R$$ in a region of constant uniform magnetic field $$\vec{B}$$.
The work $$W_1\,  and\, W_2$$ done by the magnetic field in the Two cases, respectively are such that
  • $$W_1\, =\, W_2\, =\, 0$$
  • $$W_1\, >\, W_2$$
  • $$W_1\, =\, W_2\, \neq \, 0$$
  • $$W_1\, <\, W_2$$
Which one of the following is not correct about Lorentz Force?
  • In presence of electric field $$\bar{E} (r)$$ and magnetic field $$\bar{B} (r)$$ the force on a moving electric charge is $$\bar{F} = q[\bar{E}(r) + \vec{v} \times \bar{B}(r)]$$.
  • The force, due to magnetic field on a negative charge is opposite to that on a positive charge.
  • The force due to magnetic field become zero if velocity and magnetic field are parallel or antiparallel.
  • For a static charge the magnetic force is maximum.
Two charges of same magnitude move in two circles of radii $$R_{1} = R$$ and $$R_{2} = 2R$$ in a region of constant uniform magnetic field $$B_{0}$$.
The work $$W_1$$ and $$W_2$$ done by the magnetic field in the Two cases, respectively are such that
  • $$W_{1} = W_{2} = 0$$
  • $$W_{1} > W_{2}$$
  • $$W_{1} = W_{2} \neq 0$$
  • $$W_{1} < W_{2}$$
Some current carrying wires are given in List -I and graph of variation of magnetic field versus position of point P are given in List -II. Match the graph given in List -II for the current carrying wire in List -I
332055.png
  • P-2, Q-4, R-3, S-1
  • P-2, Q-1, R-3, S-4
  • P-3, Q-4, R-1, S-3
  • P-4, Q-1, R-2, S-3
The magnetic moment of current $$(I)$$ carrying circular coil of radius $$(r)$$ and number of turns $$(n)$$ varies as
  • $$1/r^2$$
  • $$1/r$$
  • $$r$$
  • $$r^2$$
When a proton moves in a uniform magnetic field, the momentum change but its kinetic energy does not change because :
  • The magnetic force exerted will be perpendicular to the direction of motion of the proton.
  • Work done will be zero.
  • Kinetic energy does not change.
  • All
The pattern of the magnetic field around a conductor due to an electric current flowing through it depends on
  • amount of current flowing through the conductor
  • amount of voltage supplied to the conductor
  • size of conductor
  • shape of the conductor
In a long straight conductor carrying current, if the current is tripled and the distance of the point from the conductor is doubled, then the ratio of new magnetic induction to old magnetic induction is ______
396763.JPG
  • $$3:2$$
  • $$2:3$$
  • $$4:9$$
  • $$9:4$$
If two wires are carrying currents in opposite directions, then they will 
  • repel each other
  • attract each other
  • become inclined to each other
  • neither repel nor attract each other
Two circular coils made up of identical wires of length 40 cm have respectively 8 and 4 turns and the current flowing through the second coil is 4 times greater than in the first coil. The ratio of magnetic induction at their centres is :
  • 2:3
  • 3:2
  • 1:1
  • 1:2
A proton and an $$\alpha$$ particle moving with the same speed enter a uniform magnetic field. The proton enters at right angles to the field. The magnetic force $$F$$ on the particles will be the same when the direction of motion of a particle is ________.
  • Parallel to the field
  • Perpendicular to the field
  • At $$30$$ to the field
  • At $$60$$ to the field
Circular loop of a wire and a long straight wire carry currents $$I_o$$ and $$I_e$$, respectively as shown in figure. Assuming that these are placed in the same plane, the magnetic fields will be zero at the centre of the loop when the separation H is

431124.png
  • $$\displaystyle\frac{I_eR}{I_c\pi}$$
  • $$\displaystyle\frac{I_cR}{I_e\pi}$$
  • $$\displaystyle\frac{\pi I_c}{I_e R}$$
  • $$\displaystyle\frac{I_e\pi}{I_cR}$$
A long curved conductor carrier a current $$\vec{I}$$($$\vec{I}$$ is a vector). A small current element of length $$d \vec l$$, on the wire, induces a magnetic field at a point, away from the current element. If the position vector between the current element and the point is $$\vec{r}$$, making an angle $$\theta$$ with current element then, the induced magnetic field density, $$d \vec B$$ at the point is $$(\mu_0=$$permeability of free space):
  • $$\displaystyle\frac{\mu_oI (d \vec l\times \vec{r})}{4\pi r^3}$$ perpendicular to the current element $$d \vec l$$
  • $$\displaystyle\frac{\mu_oI\times \vec{r}.d \vec l}{4\pi r^2}$$ perpendicular to the current element $$d \vec l$$
  • $$\displaystyle\frac{\mu_oI\times d \vec l}{ r}$$ perpendicular to the plane containing the current element and position vector $$\vec{r}$$
  • $$\displaystyle\frac{\mu_oI\times d \vec l}{4\pi r^2}$$ perpendicular to the plane containing current element and position vector $$\vec{r}$$
A galvanometer of resistance $$50   \Omega$$ is connected to a battery of $$3   V$$ along with a resistance of $$2950   \Omega$$ in series. A full-scale deflection of $$30$$ divisions is obtained in the galvanometer. In order to reduce this deflection to $$20$$ divisions, the resistance in series should be equal to :
  • $$5050 \Omega$$
  • $$5550 \Omega$$
  • $$6050 \Omega$$
  • $$4450 \Omega$$
Magnetic induction produced at the centre of a circular loop carrying current is $$B$$. The magnetic moment of the loop of radius $$R$$ is
($${\mu_0} =$$ permeability of free space)
  • $$\dfrac{B{R}^{3}}{2\pi {\mu}_{0}}$$
  • $$\dfrac{2\pi B{R}^{3}}{{\mu}_{0}}$$
  • $$\dfrac{B{R}^{2}}{2\pi {\mu}_{0}}$$
  • $$\dfrac{2\pi B{R}^{2}}{{\mu}_{0}}$$
A wire of length L metre carrying current I ampere is bent in the form of a circle. What is the magnitude of magnetic dipole moment?
  • $$IL^2/4\pi$$
  • $$I^2L^2/4\pi$$
  • $$I^2L/8\pi$$
  • $$IL^2/8\pi$$
If magnetic field produced by a straight current carrying wire at a distance 10cm from it is X. Then the magnetic field produced at a distance 29cm will be
  • >X
  • <X
  • =X
  • all
0:0:1


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