Magnetism Question 1.
Consider a hypothetic spherical body. The body is cut into two parts about the diameter. One of hemispherical portion has mass distribution distribution m while the other portion has has identical identical charge distribution distribution q. The body is rotated about the axis with constant speed . Then, the ratio of magnetic moment to angular momentum is :
[A] [B] [C] [D] can't be calculated
Question 2.
A wire PQ wire PQ of of mass 10 g 10 g is is at rest on two horizontal parallel metal rails. The separation between the rails is 5 cm. A vertical magnetic field of 0.80 T is is applied perpendicular perpendicular to the plane of the the rails, directed directed downwards. downwards. The resistance resistance of the circuit is slowly decreased. When the resistance decreases to below the wire PQ wire PQ begins begins to slides on the rails. Calculate the coefficient of friction between the wire and the rails. ( g ( g = = 10 m/s2)
[A] [B] [C] [D]
0.08 0.12 0.18 0.50
Question 3.
Three infinitely long thin wires, each carrying current i in the same direction, are in the X -Y plane of a gravity free space. The central wire is along the y-axis while the other two are along Choose the correct option. [A]
The magnetic field is zero at
[B]
The magnetic field is zero at [C] Both (A) and (B) are correct [D] Both (A) and (B) are wrong
Question 4.
Three infinitely long thin wires, each carrying current i in the same direction, are in the X -Y plane of a gravity free space. The central wire is along the y-axis while the other two are along If the central wire is displaced along the z -direction by a small amount andreleased, show that it will execute simple harmonic motion. If the linear density of the wires is , find the frequency of oscillation. [A] [B] [C] [D]
Question 5.
The figure shows two coaxial circular loops 1 and 2, which forms same solid angle at point O. If B1 and B2 are the magnetic fields produced at the point O due to loop 1 and 2 respectively, then :
[A] [B] [C] [D]
Question 6.
A wire carrying a current of 3 A is bent in the form of a parabola as shown in figure, where x and y are in metre. The wire is placed in a uniform magnetic field tesla. The force acting on the wire is:
[A] [B] [C] [D]
Question 7.
A uniform current carrying ring of mass m and radius R is connected by a massless strings as shown. A uniform magnetic field B0 exist in the region to keep the ring in horizontal position, then the current in the ring is :
[A] [B] [C] [D]
Question 8.
Two wires wrapped over a conical frame from the coils 1 and 2. If they produce no net magnetic field at the apex P. the value of
[A] [B] [C]
[D]
Question 9.
A charge particle of mass and charge is projected with a velocity v at a distance d from a long straight current carrying conductor. The radius of curvature of the path traced by the particle at the given position does not depend on :
[A] m [B]
[C] q [D]
Question 10.
[A] [B] [C] [D]
Question 11.
A charged particle of mass enters horizontally and perpendicularly to a horizontal magnetic field of induction 1 T . If , for what value of velocity will it pass straight through the field without deflection? [A] [B] [C] [D]
Question 12.
A steady current is flowing in a circular coil of radius R, made up of a thin conducting wire. The magnetic field at the centre of the loop is B L. Now, a circular
loop of radius R/n is made from the same wire without changing its length, by unfolding and refolding the loop, and the same current is passed through it. If new magnetic field at the centre of the coil is BC , then the ratio B L /BC is : [A] 1 : n [B] n [C] n : 1 [D] None of these
Question 13.
A uniform magnetic field exists in region of space. A semicircular wire of radius 1 m carrying current 1 A having its centre at (2, 2, 0 ) is placed in x y plane as shown in figure. The force on semicircular wire will be :
[A] [B] [C] [D]
Question 14.
Determine the magnetic field at the centre of the current carrying wirer arrangement shown in Fig. The arrangement extends to infinity. (The wires joining the successive squares are along the line passing through the centre)
[A] [B] 0 [C] [D] None of these
Question 15.
In a certain region of space, there exists a uniform and constant electric field of strength E along x - axis and uniform constant magnetic field of induction Balong z -axis. A charged particle having charge q and mass m is projected with speed v parallel to x-axis from a point (a, b, 0). When the particle reaches a point 2a, b/2, 0 its speed becomes 2 v. Find the value of electric field strength in terms of m, v and co-ordinates. [A] [B] [C] [D]
Question 16.
A particle of specific charge is projected from the origin towards positives x-axis with a velocity of 10 m/ s in a uniform magnetic field Tesla. The velocity of the particle after time will be : [A] [B]
[C] [D]
Question 17.
A long straight non-conducting string carries a charge density of . It is pulled along its length at a speed of 300 m/ sec. What is the magnetic field at a normal distance of 5mm from the moving string? [A] [B] [C] [D]
Question 18.
Cyclotron is a device to speed up a charge particle to any desired speed. The principle is that a charge particle speeds up in the gap between the Dees where an alternating electric field is applied. The time of circular motion of the charge particle in the magnetic field normal to the Dees does not depend on the speed of the particle which is given as
Hence, the particle takes
to revolve a half circle.
During this time the polarity of the Dees can be changed (adjusted) so that always the particle speeds up in the gap. This is possible by synchronizing the frequency of oscillation of the electric field and frequency of revolution of the particle. In each revolution, the particle gets two impulses to increase its speed. After millions of revolutions, the particle attains suitable speeds for different purpose such as atom splitting etc. The Dees are perforated so that the stream of particles move in spiral path before emerging by the deflector. Using the above ideas answer the following questions.
The angular momentum of an accelerating charge in the cyclotron depends on r as:
[A] r [B] [C] [D]
Question 19.
If the maximum voltage across the gap is gap is 50 kV , the number of revolution to attain 100 MeV for a proton is: [A] 2000 [B] 1000 [C] 500 [D] None of these
Question 20.
[A] [B] [C] [D]
Question 21.
A particle with charge +Q and mass m enters a magnetic field of magnitude B, existing only to the right of the boundary YZ . The direction of the motion of the particle is perpendicular to the direction of B Let particle in the field will be :
, the time spent by the
[A] [B] [C] [D]
undefinedundefinedNaN Question 22. A long straight wire along the z -axis carries a current i in the negative z -direction. The magnetic vector field at a point having coordinate ( x, y) on the z = 0 plane is:
[A]
[B]
[C]
[D]
undefinedundefinedNaN Question 23. A loop and a straight wire carrying a current i are placed in the same plane as shown in the figure. Than the value of x for which zero magnetic field is produced at C is :
[A] [B] [C] [D] None of these
Question 24.
If the B- H curves of two samples P and Q of iron are as shown below. Then choose the correct statement :
[A] [B] [C] [D]
Both P and Q are suitable for making permanent magnet P is suitable for making permanent magnet and Q for making electromagnet P is suitable for making electromagnet and Q is suitable for permanent magnet Both P and Q are suitable for making electromagnets
Question 25.
In a certain region a uniform electric field E and magnetic field B are present in opposite directions. At the instant t = 0, a particle of mass m carrying a charge q is given velocity v0 at angle , with the y-axis, in the yz plane. The time after which the speed of the particle would be minimum is equal to:
[A] [B] [C] [D]
Question 26.
A particle of charge 'q' and mass 'm' enters normally (at point P ) in a region of magnetic field with speed v. It comes out normally (from point Q) after timeT as shown in figure. The magnetic field B is present only in the region of radius R and is uniform. Initial and final velocities are along radial direction and they are perpendicular to each other. For this to happen, which of the following expression is incorrect :
[A] [B] [C] Impulse of magnetic field
[D]
Work done by magnetic field =
Question 27.
Two long parallel straight conductors carry currents . When the currents are in the same direction, the magnetic field at a point midway between the wires is . If the direction of is reversed field becomes . The ratio of the currents is : [A] [B] [C] [D]
5/2 4/3 5/3 7/3
Question 28.
A wipe of length L is bent to form a circular coil of certain number of turns n. A current I is established in the coil and a uniform magnetic field B in the plane of the coil is switched on. The torque acting on the coil then is proportional to : [A] [B] [C] [D]
n 1/n n 1/n
Question 29.
A coil having n turns and resistance is connected with a galvanometer of resistance . This combination is moved in time t seconds from a magnetic flux W 1 Weber to W 2 Weber. The induced current in the circuit is : [A] [B] [C] [D]
Question 30.
A current I flows through a thin wire shaped as regular polygon of n sides which can be inscribed in a circle of radius R. The magnetic field induction at the centre of polygon due to one side of the polygon is: [A] [B] [C] [D]
Question 31.
Consider the situation shown in the figure below. The mass of the ring is ' m' and the radius is 'a' . The resistance of each semicircular part of the ring is r . The ring is free to slide down the parallel rails without friction. The rails are connected with a resistor R at the top. A magnetic field B is present and is into the page in the figure shown. The terminal velocity v of the ring is :
[A] [B] [C] [D]
Question 32.
Figure shows three infinite currents carrying wires perpendicular to the X -Y plane passing through x-axis. The direction and magnitude of current is shown in the
figure. Which of the following graphs correctly represents B y variation of magnetic field on the X-axis?
[A]
[B]
[C]
[D]
Question 33.
The figure shows a (into the Plane) long straight metal rod carrying a current I along negative Z axis. The radius of the rod is R. The rod has two holes drilled along the complete length, each of radius . Find the magnetic field at a point P on the x axis at a distance 2 R from the centre of the wire.
[A] 0 [B] [C] [D]
Question 34.
An infinitely long wire lying along z-axis carries a current I, flowing towards positive z -direction. There is no other current. Consider a circle in x- y plane with centre at (2 meter, 0, 0) and radius 1 meter. Divide the circle in small segments and let
denote the length of a small segment in anticlockwise direction, as shown.
Consider two points A(3m, 0, 0) and B(2m, 1, 0) on the given circle. The path integral of the total magnetic field from A to B is : [A] [B] [C] [D] 0
along the perimeter of the given circle
Question 35.
The maximum value of path integral of the total magnetic field perimeter of the given circle between any two points on the circle is :
along the
[A] [B] [C] [D] 0
Question 36.
From a long solid cylinder of radius R, a cylinder of radius R/2 is removed, as shown. Current flowing in the remaining cylinder is I. Magnetic field strength is:
[A] Zero at point A [B] Zero at point B [C] [D]
at point A at point B
