Contents

**NEET Physics Chapter Wise Mock Test – Magnetic Effects of Current**

**Question 1:
**Biot-Savart law indicates that the moving electrons (velocity v) produce a magnetic field B, such that

(a) B ⊥ v

(b) B || v

(c) It obey inverse cube law

(d) It is along the line joining the electron and point of observation

**Question 2:
**Magnetic field B on the axis of a circular coil far away at distance x from the centre of the coil are related as

(a) B ∝ x

^{-3}

(b) B ∝ x

^{-2}

(c) B ∝ x

^{-1}

(d) None of these

**Question 3:
**A current carrying coil is bent sharply, so as to convert it into a double loop both carrying current in the same direction. If B be the initial magnetic field at the centre, what will be the final concentric magnetic field ?

(a) 26

(b) 46

(c) 86

(d) Zero

**Question 4:
**A square wire of each side l carries a current I. What is the magnetic field at the mid-point of the square ?

**Question 5:
**A regular hexagon carries current I. The hexagon can be inscribed inside a circle of radius R. What is the magnetic field at the centre of the circle ?

**Question 6:
**An electron moves in a circular orbit with a uniform speed v. It produces a magnetic field B at the centre of the circle. The radius of the circle is proportional to

(a) B/v

(b) v/B

(c) √(v/B)

(d) √(B/v)

**Question 7:
**What is the magnetic field at the centre of arc in the figure below?

**Question 8:
**Two circular coils 1 and 2 are made from the same wire but the radius of the 1

^{st}coil is twice that of the 2

^{nd}coil. What is the ratio of potential difference applied across them, so that the magnetic field at their centres is the same?

(a) 3

(b) 4

(c) 6

(d) 2

**Question 9:
**An electron is revolving around a proton in a circular path of diameter 0.1 nm. It produces a magnetic field 4 Wm

^{-2}on the proton. What is the angular speed of the electron?

(a) 1.4x 10

^{16}rad s

^{-1}

(b) 2.2x 10

^{6}rad s

^{-1}

(c) 6.4 x 10

^{16}rad s

^{-1}

(d) 8.8 x 10

^{16}rad s

^{-1}

**Question 10:
**Infinite number of straight wires, each carrying current I are equally placed as shown in the figure. Adjacent wires have current tn opposite direction. Net magnetic field at point P, is

**Question 11:
**A current of 4×10

^{-3}A is flowing in a long straight conductor. The value of line integral of magnetic field around the closed path enclosing the straight conductor will be

(a) 1.6π x 10

^{-9}Wbm

^{-2}

(b) 1.6 x 10

^{-9}Wbm

^{-2}

(c) 1.6 x 10

^{-8}Wbm

^{-2}

(d) 1.6πx10

^{-7}Wbm

^{-2}

**Question 12:
**The magnetic field due to a straight conductor of uniform cross-section of radius a and carrying a steady current is represented by

**Question 13:
**Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field B = B

_{0}k.

(a) They have equal z-components of momenta

(b) They must have equal charges

(c) They necessarily represent a particle-anti-particle pair

(d) The charge to mass ratio satisfy : (e/m)

_{1}+ (e/m)

_{2}=0

**Question 14:
**When a charged particle moving with velocity v is subjected to a magnetic field of induction B, the force on it is non-zero. This implies that

(a) angle between v and B is necessarily 90°

(b) angle between v and B can have any value other than 90°

(c) angle between v and B can have any value other than zero and 180°

(d) angle between v and B is either zero or 180°

**Question 15:
**An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?

(a) The electron will be accelerated along the axis

(b) The electron path will be circular about the axis

(c) The electron will experience a force at 45° to the axis and hence execute a helical path

(d) The electron will continue to move with uniform velocity along the axis of the solenoid

**Question 16:
**An α-particle describes a circular path of radius r in a magnetic field B. What will be the radius of the circular path described by the proton of same energy in the same magnetic field ?

(a) r/2

(b) r

(c) √2

(d) 2r

**Question 17:
**A beam of electrons passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off and the same magnetic field is maintained, the electrons move

(a) in an elliptical orbit

(b) in a circular orbit

(c) along a parabolic path

(d) along a straight line

**Question 18:
**Under the influence of a uniform magnetic field, a charged particle is moving in a circle of radius R with constant speed v. The time period of the motion

(a) depends on v are not on R

(b) depends on both R and v

(c) is independent of both R and v

(d) depends on R and not on v

**Question 19:
**A beam of a-particles having specific charge 2.5x 10

^{7}C kg

^{-1}move with a speed of 2x 10

^{5}ms

^{-1}in a magnetic field of 0.05 T. What is the radius of the circular path described by the α-particles?

(a) 4 cm

(b) 8 cm

(c) 16 cm

(d) 32 cm

**Question 20:
**A cyclotron is used to obtain a 2 MeV beam of protons. The alternating potential difference applied between the dees has a peak value of 20 kV and its frequency is 5 MHz. The intensity of magnetic field to be applied for resonance will be

(a) 0.0327 T

(b) 0.327 T

(c) 3.27 T

(d) None of these

**Question 21:
**A charged particle q enters a region of uniform magnetic field B (out of page) and is deflected a distance d after travelling a horizontal distance a. The magnitude of the momentum of the particle is

**Question 22:
**The radius of the earth is 6.4 x 10

^{6}m. The specific charge of proton is 9.6 x10

^{7}Ckg

^{-1}. What should be the value of minimum magnetic field at the equator of earth, such that a proton moving with velocity 1.92 x 10

^{7}ms

^{-1}may revolve round the earth ?

(a) 1.57x 10

^{-8}T

(b) 3.12x 10

^{-8}T .

(c) 5.36 x 10

^{-6}T

(d) 7.83 x 10

^{-6}T

**Question 23:
**A particle of mass 1.6x 10

^{-27}kg and charge 1.6x 10

^{-19}C enters a uniform magnetic field of 1 T as shown in the figure. The speed of the particle is 10

^{7}ms

^{-1}. The distance PQ will be

**(a) 0.141m**

(b) 0.28 m

(c) 0.4m

(d)0.5m

**Question 24:
**An irregular loop carrying current 5 A is placed in a uniform magnetic field B = 0.5 T, as such straight segment AB of length 10 cm is out of magnetic field. The magnitude and the direction of the magnetic force acting on the loop are

**(a) ON and unlike parallel to BC**

(b) 0.25 N and unlike parallel to BC

(c) 0.25 N and like parallel to BC

(d) None of the above

**Question 25:
**

**Question 26:
**Current of 5A and 2A are passed through two parallel wires A and B respectively, in opposite directions. If the wire A is infinitely long and the length of the wire B is 5 m, the force on the conductor B, which is situated at 20 cm distance from A will be

(a) 5 x 10

^{-5}N

(b) 2 x 10

^{-5}N

(c) 5π x 10

^{-7}N

(d) 2π x 10

^{-7}N

**Question 27:
**A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moment p is given by

(a) qvR/2

(b) qvR

^{2}

(c) qvR

^{2}/2

(d) qvR

**Question 28:
**What is the magnetic dipole moment of an electron orbiting around a nucleus in a circular orbit of radius 53 rpm? The orbital speed of the electron is 2.185 x 10

^{6}ms

^{-1}.

(a) 1.6x 10

^{-19}Am

^{2}

(b) 5.3x 10

^{-21}Am

^{2}

(c) 9.3x 10

^{-24}Am

^{2}

(d) None of these

**Question 29:
**The magnetic moment of the current carrying loop as shown in figure, is equal to

**Question 30:
**An insulation rod of length l carries a charge q distributed uniformly on it. The rod is pivoted at an end and is rotated at a frequency f about a fixed perpendicular axis. The magnetic moment of the system is

(a) zero

(b) πqfl

^{2}

(c) 1/2 πqfl

^{2}

(d) 1/3 πqfl

^{2}

**Question 31:
**A coil of 100 turns is lying in a magnetic field of 1 T as shown in the figure. A current of 1A is flowing in this coil. The torque acting on the coil will be

**(a) 1 Nm**

(b) 2 Nm

(c) 3 Nm

(d) 4 Nm

**Question 32:
**A coil in the shape of an equilateral triangle of side l is suspended between the pole pieces of a permanent magnet, such that B is in plane of the coil. If due to a current I in the triangle, a torque T acts on it. The side l of the triangle is

**Question 33:
**An infinitely long wire is bent at 90° at point O as shown in figure. Match the following

**Direction (Q. Nos. 34-39):** In each of the following questions, a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statement, mark the correct answer as

(a) If both Assertion and Reason are true and Reason is the correct explanation of the Assertion

(b) If both Assertion and Reason are true but the Reason is not the correct explanation of Assertion

(c) If Assertion is true but Reason is false

(d) If both Assertion and Reason are false

**Question 34:
Assertion (A): **Cyclotron does not accelerate electron.

**Mass of the electron is very small.**

Reason (R):

Reason (R):

**Question 35:
Assertion (A): **The magnetic field at the centre of the circular coil, in the following figure is zero.

**l**

Reason (R):

Reason (R):

_{1}=l

_{2}, therefore the magnetic field due to one part balances that due to the other part of the circle.

**Question 36:
Assertion (A): **In electric circuits, wires carrying currents in opposite directions are often twisted together.

**If the wire are not twisted together, the combination of the wires forms a current loop. The magnetic field generated by the loop might affect adjacent circuits or components.**

Reason (R):

Reason (R):

**Question 37:
Assertion (A): **The magnetic field at a point near the centre but outside a current carrying solenoid is zero.

**The magnetic field is zero because two halves of the solenoid produce equal and opposite magnetic fields.**

Reason (R):

Reason (R):

**Question 38:
Assertion (A): **A neutron enters in a magnetic field of strength B perpendicular to the magnetic lines of force, with speed v, the magnetic force on the neutron is zero.

**Charge on neutron is zero.**

Reason (R):

Reason (R):

**Question 39:
**A current I amp flows along an infinitely long straight thin walled tube. The magnetic induction at any point inside the tube at a distance r metre from axis, is

(a) 0

(b) ∞

(c) μ

_{0}l/2r

(d) μ

_{0}l/2πr

**Question 40:
**A wire carrying current I has the shape as shown in adjoining figure. Linear parts of the wire are very long and parallel to X-axis while semi-circular portion of radius R is lying in YZ-plane. Magnetic field at point O is

**Question 41:
**An electron moving in a circular orbit of radius r, makes n rotations per second. The magnetic field produced at the centre has magnitude

**Question 42:
**A conducting square frame of side a and a long straight wire carrying current I are located in the sample plane as shown in the figure. The frame moves to the right with a constant velocity v. The emf induced in the frame will be proportional to

**Question 43:
**Two identical along conducting wires AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry l

_{1}and l

_{2}currents, respectively. Point P is lying at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be

**Question 44:
**In an ammeter 0.2% of main current passes through the galvanometer. If resistance of galvanometer is G,the resistance of ammeter will be

(a) G/499

(b) 499G/500

(c) G/500

(d) 500G/499

**Question 45:
**A uniform electric field and an uniform magnetic field are produced, pointed in the same direction. An electron is projected with its velocity pointing in the same direction

(a) the electron will turn to its left

(b) the electron will turn to its right

(c) the electron velocity will increase in magnitude

(d) the electron velocity will decrease in magnitude

**Question 46:
**A current loop in a magnetic field

(a) experiences a torque, whether the field is uniform or non-uniform in all orientations

(b) can be in equilibrium in one orientation

(c) can be equilibrium in two orientations, both the equilibrium states are unstable

(d) can be in equilibrium in two orientations, one stable while the other is unstable

**Question 47:
**When a proton is released from rest in a room, it starts with an initial acceleration a

_{0}towards West. When it is projected towards North with a speed v

_{0}, it moves with an initial acceleration 3a

_{0}towards West. The electric and magnetic fields in the room are

**Question 48:
**A rectangular loop carrying a current I is situated near a long straight wire, such that the wire is parallel to one of the sides of the loop and is in the plane of the loop. If a steady current I is established in the wire as shown in the figure, the loop will

(a) rotate about an axis parallel to the wire

(b) move away from the wire

(c) move towards the wire

(d) remain stationary

**Question 49:
**A magnet of dipole moment 2 Am

^{2}is deflected through 30° from magnetic meridian. The required deflecting torque is (BH = 0.4 x 10

^{-4})

(a) 0.4 x 10

^{-4}Nm

(b) 0.4 Nm

(c) 0.2 x 10

^{-4}N m

(d) None of these

**Question 50:
**In the circuit shown the cells A and B have negligible resistances. For V

_{A}=12 V, R

_{1}=500 Ω and R = 100 Ω the galvanometer (G) shows no deflection. The value Of VB is

**(a) 4 V**

(b) 2 V

(c) 12 V

(d) 6V

**Question 51:
**A millivoltmeter of 25 mV range is to be converted into an ammeter of 25 A range. The value (in Ω) of necessary shunt will be

(a) 0.001

(b) 0.01

(c) 1

(d) 0.05

**Question 52:
**If a shunt of 1/10 th of the coil resistance is applied to a moving coil galvanometer, its sensitivity becomes

(a) 10 fold

(b) 1/10 fold

(c) 11 fold

(d) 1/11 fold

**Question 53:
**A circular loop and a square loop are formed from the same wire and the same current is passed through them. Find the ratio of their dipole moments.

(a) 4π

(b) 4/π

(c) 2/π

(d) 2π

**Question 54:
Assertion (A): **Magnetic field due to an infinite straight conductor varieg inversely as the distance from it.

**The magnetic field at the center of the circular coil in the following figure is zero.**

Reason (R):

Reason (R):

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion

(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion

(c) If Assertion true but Reason is false

(d) If both Assertion and Reason are false

**Question 55:
**A thin ring of radius R metre has charge q coulomb uniformly spread on it. The ring rotates about its axis with a constant frequency of f revolution/s. The value of magnetic induction in Wb m

^{-2}at the center of the ring is

**Question 56:
**A conducting circular loop is placed in a uniform magnetic field, B = 0.025 T with its plane perpendicular to the loop. The radius of the loop is made to shrink at a constant rate of 1 mms

^{-1}. The induced emf when the radius is 2 cm, is

(a) 2πμV

(b) πμV

(c) π/2 μV

(d) 2μV

**Question 57:
**A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is F, the net force on the remaining three arms of the loop is

(a) 3 F

(b) -F

(c) -3F

(d) F

**Question 58:
**A square conducting loop of side length L carries a current I. The magnetic field at the centre of the loop is

(a) independent of L

(b) proportional to L

^{2}

(c) inversely proportional to L

(d) linearly proportional to L

**Question 59:
**Torques τ

_{1}, and τ

_{2}are required for magnetic needle to remain perpendicular to the magnetic field B

_{1}and B

_{2}at two different places. The ratio B

_{1}/B

_{2}is

**Question 60:
**Magnetic field at the centre of a circular loop of area A is B. The magnetic moment of the loop will be

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