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Magnetostatics(3.1)
Level 1
1. The magnitude of the B-field due to a moving charge is greatest when the angle
between L and r is Ans:B
A) 0o
B) 90o
C) magnitude independent of angle
D) None
2. Which of the following can produce a region with a uniform B-field?
Ans:C
A) moving charge
B) straight wire carrying current
C) solenoid D) None
3. If a current is passed through one of two closely spaced metal rods and the
other rod moves away, the other rod must have a current that is
A) parallel
B) anti-parallel
Ans:B
C) zero D) A and B
4. Whose law relates a magnetic function to current? Ans:B
A) Gauss’s law for magnetism
B) Ampere’s law for magnetism
C) Gauss’s law for electricity
D) Newton’s Law
5. If current flows clockwise as seen from above through a horizontal wire loop, the
magnetic field at the center of the loop is directed
A) up
B) down
Ans :B
C) no field at center of loop
6. If Object X attracts Y (X never repel Y) then which is false statement Ans:c
a) X is magnet
b) Y is iron
c)X and Y are magnet
d)X is magnet and Y is iron
7. Which of the following is true? Ans:A
A) a closed surface determines a unique volume
B) a unique boundary determines a unique surface
C) both are true
D) neither are true
8. What is the pitch of a solenoid? Ans:C
A) number of loops
B) length L of coil
C) ratio of number to length D) None
D) A and B
9. Who came up with the idea of a displacement current? Ans:D
A) Newton
B) Coulomb
C) Gauss
D) Maxwell
E) Ampere
10.One of the following is not a source of magnetostatic fields:
A) A dc current in wire
B) A permanent magnet
C) An accelerated charge
D) A charge disk rotating at uniform speed
E) An electric field linearly changing with time
Level 2
11. Which of the following choices correctly indicates the relationship between the magnetic field due to
a current carrying, long straight wire at a distance R from the wire?Ans:b
a)B=kR
b)B=k/R
c)B=kR2
d)B=k/R2
12. The magnetic field B at a distance r from a long straight wire is measured. What
will the magnetic field B be at a point twice as far from the wire? Ans:B
A) doubled
B) halved
C) quadrupled
D) quartered
13. What is the radius of the path of an electron (mass 9 × 10-31 kg and charge 1.6 × 10–19 C) moving at a
speed of 3 ×107 m/s in a magnetic field of 6 × 10–4 T perpendicular to it? Ans:a
a)26cm
b)26m
b)36m
c)36cm
14. Refer Question 13 , find what is its frequency? Ans:c
a)1MHz
b)3MHz
c)2MHz
d)4MHz
15.Refer question 13 , Calculate energy of electron in electron volts(eV)? Ans:a
a)2.5k
b)3.5k
c)5k
d)7.67k
16. A solenoid of length 0.5 m has a radius of 1 cm and is made up of 500 turns. It carries a current of
5A. What is the magnitude of the magnetic field inside the solenoid? Ans:c
a)3.14T
b)3.14 mT
c)6.28 mT
d)6.28T
17. A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What
is the magnitude of the magnetic field B at the centre of the coil? Ans:c
a)1000uT
b)10uT
c)100uT
d)1uT
18. A horizontal overhead power line carries a current of 90 A in east to west direction. What is the
magnitude and direction of the magnetic field due to the current 1.5 m below the line? Ans:a
a)12 uT ,toward south
b)12uT ,toward North
b) 1.2 uT toward south
d)1.2 uT ,toward North
19. A 3.0 cm wire carrying a current of 10 A is placed inside a solenoid perpendicular to its axis. The
magnetic field inside the solenoid is given to be 0.27 T. What is the magnetic force on the wire? Ans:a
a)0.81 mN
b)81mN
c)8.1 mN
d)810mN
20.What is the magnitude of magnetic force per unit length on a wire carrying a current of 8 A and
making an angle of 30º with the direction of a uniform magnetic field of 0.15 T?Ans:b
a)6 Nm-1
b) 0.6 Nm-1
c) 8 Nm-1
d)0. 8 Nm-1
Level 3
21.Give the signs of the potential difference VP – VQ; VB – VA.
A)positive,negative
B)negative ,positive
C)negative,negative
D)positive,positive
Ans:B
22.Give the sign of the potential energy difference of a small negative
charge between the points Q and P; A and B.
Ans:D
A)positive,negative
B)negative ,positive
C)negative,negative
D)positive,positive
23.Give the sign of the work done by the field in moving a small
positive charge from Q to P.
Ans:B
A)positive
B)negative
C)insufficient data
D)none
24.Give the sign of the work done by the external agency in moving
a small negative charge from B to A.
Ans:A
A)positive
B)negative
C)insufficient data
D)none
25.Does the kinetic energy of a small negative charge increase or
decrease in going from B to A?
Ans:B
A)Increase
B)Decrease
C)insufficient data to calculate
D)none
21. Which one of the following statement concerning Ampere’s law for static magnetic fields is false?
Ans:a
a) The strength of the magnetic field produced by the current is not dependent on the distance from the
current geometry that produces the magnetic field.
b) A closed path of arbitrary shape is constructed around the current.
c) This law may be applied to any current geometry that produces a magnetic field that does not change
with time.
d) The permeability of free space is a constant that appears in Ampere’s law.
22. Consider two parallel wires carrying current in the same direction. Which one of the following
statements to true concerning this situation? Ans:a
a) The two wires will attract each other, even if no external magnetic field is applied to the wires.
b) The two wires will repel each other, even if no external magnetic field is applied to the wires.
c) The two wires will attract each other, only if an external magnetic field is applied to the wires.
d) The two wires will repel each other, only if an external magnetic field is applied to the wires.
23. Consider two parallel wires carrying current in opposite directions. Which one of the following
statements to true concerning this situation? Ans:b
a) The two wires will attract each other, even if no external magnetic field is applied to the wires.
b) The two wires will repel each other, even if no external magnetic field is applied to the wires.
c) The two wires will attract each other, only if an external magnetic field is applied to the wires.
d) The two wires will repel each other, only if an external magnetic field is applied to the wires.
24. Which one of the following parameters is not used to determine the magnetic force on a currentcarrying wire in a magnetic field? Ans:b
a) length of the wire
b) radius of the wire
c) direction of the magnetic field with respect to the direction of the current
d) the strength of the magnetic fielde) the magnitude of the electric current
25. Under which of the following conditions is Ampere’s law most easily applied? Ans:d
a) the currents are all in the same direction
b) the magnetic fields are spherically symmetrical
c) no currents are present within the system
d) the magnetic fields are cylindrically symmetric
26. Which one of the following statement concerning Ampere’s law for static magnetic fields is false?
Ans:a
a) The strength of the magnetic field produced by the current is not dependent on the distance from the
current geometry that produces the magnetic field.
b) A closed path of arbitrary shape is constructed around the current.
c) This law may be applied to any current geometry that produces a magnetic field that does not change
with time.
d) The component of the magnetic field that is parallel to the closed path is used in Ampere’s law.
27. The coils of a solenoid are stretched so that the length of the solenoid is twice its original length.
Assuming the same current is passed though the solenoid before and after it is stretched, how does the
magnetic field inside the solenoid change, if at all, as a result of the stretching? Ans:b
a) The magnetic field after the stretching is one-fourth the value it was before stretching.
b) The magnetic field after the stretching is one-half the value it was before stretching.
c) The magnetic field after the stretching is the same as the value it was before stretching.
d) The magnetic field after the stretching is twice the value it was before stretching.
28. A magnetic field is generated by a current-carrying wire. Which one of the following statements
concerning this situation is false?Ans:d
a) The magnitude of this magnetic field decreases with increasing distance away from the wire.
b) A right-hand rule is useful for determining the direction of the magnetic field at a particular location.
c) The magnitude of the magnetic field is directly proportional to the magnitude of the current.
d) The magnetic field is parallel to the direction of the current in the wire.
29. Two circular loops carry identical currents, but the radius of one loop is twice that of the other. How
do the magnetic fields at the centers of the loops compare? Ans:d
a) In both cases, the magnetic field at the center would be zero tesla.
b) The magnetic field at the center of the larger loop is twice that at the center of the smaller loop.
c) The magnetic field at the center of the larger loop is the same as that at the center of the smaller
loop.
d) The magnetic field at the center of the larger loop is one-half that at the center of the smaller loop.
30. Two identical coils have two different steady currents flowing through them. If the current through
the first coil is half the current through the second one, the emf across the first coil, compared to the
emf across the second, is
Ans:C
A) twice
B) half
C) same