All India Radio AIR and DD Engineering Assistants Solved Question Paper

All India Radio (AIR) and DD Engineering Assistants Solved Question Paper

1. A current carrying coil is subjected to a uniform magnetic field. The coil will orient so that its
plane becomes    ?
(a) inclined at 45° to the magnetic field
(b) inclined at any arbitrary angle to the
magnetic field
(c)   parallel to the magnetic field
(d)   perpendicular to magnetic field
Ans:c


2. Tesla is the unit of
(a)    magnetic flux
(b)    magnetic field
(c)    magnetic induction
(d)    magnetic moment
Ans:b


3. Energy in a current carrying coil is stored in the
form of   ?
(a) electric field
(b) magnetic field
(c) dielectric strength
(d) heat
Ans:b


4. The total charge induced in a conducting loop when it is moved in magnetic field depends on?
(a) the rate of change of magnetic flux
(b) initial magnetic flux only
(c) the total change in magnetic flux
(d) final magnetic flux only.
Ans:c


5. The magnetic induction at a point P which is at the distance of 4 cm from a long current carrying wire is 10-3 T. The field of induction at a distance 12 cm from the current will be ?
(a) 3.33 x 10-4 T
(b) 1.11x 10-4 T
(c) 3×10-3 T
(d) 9×10-3 T
Ans:a


6. A charge moving with velocity v in X-direction is subjected to a field of magnetic induction in negative X-direction. As a result, the charge will
(a) remain unaffected
(b) start moving in a circular path in Y—Z plane
(c) retard along X-axis
(d) moving along a helical path around X-axis
Ans:a


7. A uniform magnetic field acts right angles to the direction of motion of electrons. As a result, the electron moves in a circular path of radius 2cm. If the speed of electrons is doubled, then the radius of the circular path will be ?
(a)2.0 cm
(b) 0.5 cm
(c)4.0cm
(d) 1.0cm
Ans:c


8. A deuteron of kinetic energy 50 keV is describing a circular orbit of radius 0.5 metre in a plane perpendicular to magnetic field B. The kinetic energy of the proton that describes a circular orbit of radius 0.5 metre in the same plane with
the same B is
(a)25 keV
(b) 50 keV
(c)200 keV
(d) 100 keV
Ans:d


9. A straight wire of length 0.5 metre and carrying a current of 1.2 ampere is placed in uniform magnetic field of induction 2 Tesla. The magnetic field is perpendicular to the length of the wire. The force on the wire is ?
(a) 2.4N
(b) 1.2N
(c) 3.0 N
(d) 2.0 N
Ans:b


10. To convert a galvanometer into an ammeter, one needs to connect a ?
(a) low resistance in parallel
(b) high resistance in parallel
(c) low resistance in series
(d) high resistance in series.
Ans:a


11. A coil carrying electric current is placed in uniform magnetic field
(a) torque is formed
(B) e.m.f is induced
(c) both (a) and (b) are correct
(d) none of the above
Ans:a


12. The magnetic field at a distance ‘r’ from a long wire carrying current ‘i’ is 0.4 Tesla. The magnetic field at a distance ‘2r’ is ?
(a)0.2Tesla
(b) 0.8 Tesla
(c)0.1 Tesla
(d) 1.6 Tesla
Ans:a
13. A electron enters a region where magnetic (B) and electric (E) fields are mutually
perpendicular, then ?
(a) it will always move in the direction of B
(b) it will always move in the direction of E
(c) it always possesses circular motion
(d) it can go un deflected also.
Ans:d


14. A straight wire of diameter 0.5 mm carrying a current of 1 A is replaced by another wire of I mm diameter carrying same current. The strength of magnetic field far away is?
(a) twice the earlier value
(b) same as the earlier value
(c) one-half of the earlier value
(d) one-quarter of the earlier value
Ans:b


15. At what distance from a long straight wire carrying a current of 12 A will the magnetic field
be equal to 3×10-6 Wb/metre Square
(a) 8×10-2 m
(b) 12×10-2 m
(c)18x 10-2 m
(d) 24×10-2 m
Ans:a


16. 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) B/v
(c) √(v/B)
(d)v/B
Ans:d


17. A 10 eV electron is circulating in a plane at right angles to a uniform field at magnetic induction 10-4 Wb/m2 (= 1.0 gauss). The orbital radius of the electron is ?
(a) 12cm
(b) 16cm
(c) 11cm
(d) 18cm
Ans:c


18. A galvanometer acting as a voltmeter will have?
(a) a low resistance in series with its coil.
(b) a high resistance in parallel with its coil
(c) a high resistance in series with its coil
(d) a low resistance in parallel with its coil
Ans:c


19. A beam of electrons is moving with constant velocity in a region having simultaneous perpendicular electric and magnetic fields of strength 20 Vm-1 and 0.5 T respectively at right angles to the direction of motion of the electrons. Then the velocity of electrons must be?
(a) 8m/s
(b) 20 m/s
(c) 40m/s
(d) 1/40 m/s
Ans:c


20. A galvanometer of resistance 20 Ohms gives full scale deflection with a current of 0.004 A. To convert it into an ammeter of range 1 A, the required shunt resistance should be?
(a) 0.38 Ohms
(b) 0.21 Ohms
(c) 0.08 Ohms
(d) 0.05 Ohms
Ans:c


21. A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of the magnetic field is ?
(a) 4B
(b) B/2
(c) B
(d) 2B
Ans:c
22. A positively charged particle moving due east enters a region of uniform magnetic field directed vertically upwards. The particle will
(a) continue to move due east
(b) move in a circular orbit with its speed unchanged
(c) move in a circular orbit with its speed increased
(d) gets deflected vertically upwards.
Ans:b
23. Two long parallel wires are at a distance of 1 metre. Both of them carry one ampere of current The force of attraction per unit length between the two wires is?
(a)2 x10-7 N/m
(b) 2 x10-8 N/m
(c) 5×10-8 N/m
(d)10-7 N/m
Ans:a


24. A galvanometer having a resistance of 8 ohms is shunted by a wire of resistance 2 ohms. If the total current is 1 amp, the part of it passing through the shunt will be?
(a)0.25 amp
(b) 0.8 amp
(c)0.2 amp
(d) 0.5 amp
Ans:b


25. A coil of one turn is made of a wire of certain length and then from the same length a coil of two turns is made. If the same current is passed in both the cases, then the ratio of the magnetic inductions at their centres will be?
(a)2:1
(b)1:4
(c)4:1
(d)1:2
Ans:b


26. Magnetic field intensity in the centre of coil of 50 turns, radius 0.5 m and carrying a current of
2A is ?
(a) 0.5 x 10-5 T
(b) 1.25x 10-4 T
(c) 3x 10-5 T
(c) 4 x 10-5 T
Ans:b


27. When a proton is accelerated through I V, then its kinetic energy will be?
(a)1840 eV
(b) 13.6eV
(c)1 eV
(d) 0.54eV
Ans:c
28. If a long hollow copper pipe carries a current,thin magnetic field is produced
(a)inside the pipe only
(b)outside the pipe only
(c)both inside and outside the pipe
(d) no where
Ans:b


29. A charged particle moves through a magnetic field in a direction perpendicular to it. Then the
(a) velocity remains unchanged
(b) speed of the particle remains unchanged
(c) direction of the particle remains unchanged
(d) acceleration remains unchanged
Ans:b


30. Two long parallel wires P and Q are both perpendicular to the plane of the paper with distance of 5 m between them. If P and Q carry current of 2.5 amp and 5 amp respectively in the same direction, then the magnetic field at a point half-way between the wires is ?
(a)3µ/2∏
(b)µ/∏
(c)√3µ/2∏
(d)µ/2∏
Ans:a


31. A proton moving with a velocity 3 x 105 m/s enters a magnetic field of 0.3 Tesla at an angle of 30° with the field. The radius of curvature of its path will be (e/m for proton – 108 C/kg)
(a)2cm
(b) 0.5 cm
(c)0.02 cm
(d) 1.25 cm
Ans:b
32. A charged particle of charge q and mass m enters perpendicularly in a magnetic field B. Kinetic energy of the particle is E; then frequency of rotation is?
(a)qB/m∏
(b) qB/2m∏
(c)qBE/2m∏
(d) qB/2E∏
Ans:b


33. A galvanometer can be converted into a voltmeter by connecting?
(a) A high resistance in parallel
(b) A low resistance in series
(c) A high resistance in series
(d) A low resistance in parallel
Ans:c


34. A wire carries a current. Maintaining the same current it is bent first to form a circular plane coil of one turn which produces a magnetic field B at the centre of the coil. The same length is now bent more sharply to give a double loop of smaller radius. The magnetic field at the centre of the double loop, caused by the same current is ?
(a)4B
(b) B /4
(c) B/2
(d) 2B
Ans:a


35.A bar magnet is oscillating in earth’s magnetic field with a period T. What happens to its period of motion, if its mass is quadruped ?
(a) Motion remains simple harmonic with new period =T/2
(b) Motion remains simple harmonic with new period = 2 T
(c) Motion remains simple harmonic with new period =4T
(d) Motion remains simple harmonic and the period stays nearly constant
Ans:b


36. The work done in turning a magnet of magnetic moment M by an angle of 90° from the meridian, is n times the corresponding work done to turn it through an angle of 60°.
The value of n is given by
(a)2
(b) 1
(c) 0.5
(d) 0.25
Ans:a


37 . For protecting a sensitive equipment from the external electric arc, it should be ?
(a) Wrapped with insulation around it when passing current through it
(b) Placed inside an iron can
(c) Surrounded with fine copper sheet
(d) Placed inside an aluminium can
Ans:b
38. If a diamagnetic substance is brought near north or south pole of a bar magnet, it is?
(a) attracted by the poles
(b) repelled by the poles
(c) repelled by north pole and attracted by the south pole
(d) attracted by the north pole and repelled by the south pole
Ans:b


39. Current i is flowing in a coil of area A and number of turns N, then magnetic moment of
the coil is M= ?
(a) NiA
(b) Ni/A
(c)Ni/√A
(d) N2Ai
Ans:a


40. Two magnets of magnetic moments M and 2M are placed in a vibration magnetometer, with the identical poles in the same direction. The time period of vibration is T1. If the magnets are placed with opposite poles together and vibrate with time period T2 then ?
(a) T2 is infinite
(b) T2=T1
(c)T2>T1
(d) T2 is less than T1
Ans:c


41. A diamagnetic material in a magnetic field moves
(a) perpendicular to the field
(b) from stronger to the weaker pans of the field
(c) from weaker to the stronger parts of the field
(d) in none of the above directions
Ans:b


42. According to Curie’s law, the magnetic susceptibility of a substance at an absolute
temperature T is proportional to?
(a) T2
(b) 1/T
(c) T
(d) 1/T2
aNS (B)