Video Lecture
Theory For Notes Making
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Objective Assignment
Q.1
A long vertical straight conductor (not shown) is placed at O in figure, carries an inward current of 5 A. A small straight wire X of length 0.03 m is placed along the tangent to the circle of centre O and radius 0.1m as shown. If X carries a current of 2A, the force on X in N is
(a) 9 ´ 10-7 (b) 6 ´ 10-7 (c) zero (d) 3 ´ 10-7
Ans. (c)
Q.2
A long current-carrying wire W is free to move when placed in a magnetic field B at right angles to the field as shown
(a) it will move along the magnetic field to the right
(b) it will move upwards towards you
(c) it will move downwards away from you
(d) it will not move at all
Ans. (c)
Q.3
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 loop. If a steady current I is established in the wire as shown in fig., 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
Ans : (c)
Q.4
A circular coil of wire carries a current. PQ is part of a very long wire carrying a current and passing close to the circular coil. If the direction of the current are as shown in the figure. Then the direction of the force acting on PQ will be
(a) parallel to PQ, towards P
(b) parallel to PQ, towards Q
(c) at right angles to PQ, to the right
(d) at right angles to PQ, to the left
Ans : (d)
Q.5
In the figure, X and Y are two long straight conductors each carrying a current of 2 A. The force on each conductor is F. When the current in each is changed to 1 A and reversed in direction, the force on each is now
(a) F/4 and unchanged direction
(b) F/2 and reversed direction
(c) F/2 and unchanged direction
(d) F/4 and reversed direction
Ans. (a)
Q.6
P, Q and R are long parallel straight wires equally spaced in air, carrying current as shown in the figure. What is the direction of the resultant force on Q?
(a) to the left
(b) to the right
(c) perpendicular to plane of paper and direction inside
(d) perpendicular to plane of paper and direction upward
Ans : (b)
7.
A 3.0 cm wire carrying a current of 10A is placed inside a solenoid perpendicular to its axis. The magnetic field inside the solenoid is given to the 0.27 T. What is the magnetic force on the wire?find the force experienced by the conductor.
(a) 8.1\times {{10}^{{2}}}N
(b) 7.5\times {{10}^{{-2}}}N
(c) 8.1\times {{10}^{{5}}}N
(d) 8.1\times {{10}^{{-2}}}N
Ans (d)
8.
A conductor of length 20 cm is placed
(i)
parallel
(a)zero
(b)3
(c)9
(d)15
Ans (a)
(ii)
perpendicular
(a)0.8N
(b)0.2N
(c)1.0N
(d)2.5N
Ans (a)
(iii)
inclined at an angle 30°, to a uniform magnetic field of 2T. If the charge of 10 C passes through it in 5s.
(a)0.4N
(b)0.8N
(c)1.5N
(d) 2.0N
Ans (a)
9.
A long horizontal rigidly supported wire carries a current of 100A. Directly above it and parallel to it is a fine wire that carries a current of 200A and weighs 0.05 N/m. How far above the lower wire should the fire wire be kept to support it by magnetic repulsion?
(a)2 cm
(b) 4 cm
(c)6 cm
(d)8 cm
Ans (d)
10.
Find the magnetic force on segment PQ, due to a current of 5A flowing in it, if it is placed in a magnetic field of 0.25 T.
(a)0.20 N
(b)0.28 N
(c)0.35 N
(d)0.50 N
Ans (b)
11.
A current of 10A flows through each of two parallel long wires. The wires are 5 cm apart. Calculate the force acting per unit length of each wire. Use the standard value of constant required.
(a) 5\times {{10}^{{-4}}}N{{m}^{{-1}}}
(b) 9\times {{10}^{{-4}}}N{{m}^{{-1}}}
(c) 3\times {{10}^{{-4}}}N{{m}^{{-1}}}
(d) 4\times {{10}^{{-4}}}N{{m}^{{-1}}}
Ans(d)
12.
A short conductor of length 5.0 cm is placed parallel to a long conductor of length 1.5 cm near its center. The conductors carry currents 4.0 A and 3.0 A respectively in the same direction. What is the total force experienced by the ling conductor, when they are 3.0 cm apart?
(a) 2\times {{10}^{{-2}}}N
(b) 4\times {{10}^{{6}}}N
(c) 5\times {{10}^{{-6}}}N
(d) 4\times {{10}^{{-6}}}N
Ans (d)
13.
Two straight long parallel wires A and B carry currents of 5A and 10A respectively in opposite directions. The distance between the two wires is 0.1 m. Calculate the force on a 0.2 m section of the sire B near its center.
(a) 5\times {{10}^{{-5}}}\,N
(b) 2\times {{10}^{{5}}}\,N
(c) 2\times {{10}^{{-5}}}\,N
(d) 5\times {{10}^{{5}}}\,N
Ans (c)
Subjective Assignment
Q.1.
A current carrying loop, free to turn, is placed in a uniform magnetic field B. What will be its orientation, relative to B in the equilibrium state ‘?
Q.2
If current is passed through a spring it contracts .why ?
Q.3
Two conductors carrying current in the same direction attract each other where as two electron beams moving in the same direction repel each other .why ?
Q.4
How will you arrange two conductors carrying current, in such a way that no force will act between them ?
Q.5
How will you arrange a circular coil and a straight conductor carrying current , in such a way that no force will act between them?
Q.6.
What is the force that a conductor dl , carrying a current I, experiences when placed in a magnetic field B ‘? What is the direction of the force ?
Q.7.
Derive the expression for the force between two infinitely long parallel straight wires carrying current in the same direction. Hence define one ampere.
Q.8.
Derive an expression for the force experienced by a current carrying straight conductor placed in a magnetic field. Under what condition is this force maximum?
Q.9.
What is the magnitude of force on a wire of length 0.04 m placed inside a solenoid near its centre making an angle 30o with its axis ? The wire carries a current of 12 A and the magnetic field due to the solenoid has a magnitude of 0.25 T. [Ans. 0.06N]
Q.10
A conductor of length 20cm and mass 20gm is placed on an inclined plane with its length parallel to the horizontal plane. If the inclined plane makes an angle of 30o with the horizontal then find the magnitude of a vertical magnetic field required to avoid the slipping of the conductor down the plane. Assuming the current in the conductor to be 5amp. and the plane as frictionless.
Q.11
In the following diagram find the magnitude and direction of the force acting on the rectangular coil
Q.12
Find the force acting on the horizontal conductor due to the vertical conductor shown in the diagram.
Q.13
Two parallel wires 1m apart carry a current of 1amp and 3amp in opposite direction.Calculate the force acting per unit length between them
(a) when both are kept in free space
(b) when both are kept in water of relative permeability 0.022
Q.14
A conductor lies along z axis at -1.5 \displaystyle \le z \displaystyle \le 1.5 m and carries a fixed current of 10A in the -z direction. If the magnetic field in that region is B= 3×10-4 e \displaystyle \mu -0.2x j.Find the work and power required to move the conductor at constant speed to x = 2m and y = 0 in 5milli sec. Assume parallel motion along x axis.
Q.15
Two identical long conductors are hung from the same plane with the help of cords each of length 4cm. When equal and opposite current of 50amp is allowed to pass through them they are found to repel each other till their cords make 60o with each other.If the length of each conductor is 10cm find the mass of the conductors.
Q.16
Find the magnitude and direction of a force vector acting on a unit length of a thin wire, carrying a current I = 8.0 A , at a point O, if the wire is bent as shown in
(A) (a) with curvature radius r = 10cm.
(B) (b) the distance between the long parallel segments of the wire being equal to L = 20 cm.