Untitled Document

Question Bank No: 1

1. Magentic meridian is a

a)		point
b)		line along NS
c)		horizontal plane
d)		vertical plane along NS

2. To shield an instrument from external magnetic field, it is placed inside a cabin made of

a)		wood
b)		ebonite
c)		iron
d)		diamagnetic substance

3. The magnetising field of 2 $\times 10^{3}$ emp/m produces a magnetic flux densisty of 8 $π$ testa in an iron rod. The relative permeability of the rod will be

a)		$10^{2}$
b)		$10^{0}$
c)		$10^{3}$
d)		$10^{4}$

4. Which of the following has low value for ferrite?

a)		conductivity
b)		permeability
c)		susceptibility
d)		none of these

5. The susceptibility of paramagnetic material is K at 27 degree C. At what temperature will its susceptibility be K/2?

a)		$600^{0} c$
b)		$287^{0} c$
c)		$54^{0} c$
d)		$327^{0} c$

6. Unit of magnetic permeability is _____

a)		A $m^{- 1}$
b)		A $m^{- 2}$
c)		H
d)		H $m^{- 1}$

7. Time period of oscillation of a magnet is 2sec. When it is remagnetised so that its pole strength is 4 times, its period will be

a)		4 sec
b)		2 sec
c)		1 sec
d)		8 sec

8. A magnetic needle suspended freely orients itself

a)		in a definite direction
b)		in no direction
c)		upward
d)		down ward

9. A certain amount of current when flowing in a properly set tangent galvano meter, produces a deflection of $45^{0} .$ If the current be reduced by a factor of $\sqrt{3}$ the deflection would

a)		decrease by $30^{0}$
b)		decrease by $15^{0}$
c)		increase by $15^{0}$
d)		increase by $30^{0}$

10. The narrowest hysteresis loop is for

a)		cobalt steel
b)		almic
c)		perm alloy
d)		stainless steel

11. The permanent magnetic moment of atom or molecules of a diamagnetic material is

a)		small
b)		large
c)		negative
d)		zero

12. Platinum is

a)		dia magnetic
b)		Para magnetic
c)		ferro magnetic
d)		non magnetic

13. When a small magnetic field H is applied to a magentic material, the intensity of magnetisation is proportional to

a)		H
b)		$H^{2}$
c)		$H^{1 / 2}$
d)		$H^{- 2}$

14. When a magnet is placed vertically on a horizontal board, number of neutral points obtained on the board is

a)		four
b)		three
c)		two
d)		one

15. Lines passing through points of zero declination are

a)		isogonic line
b)		isoclinic lines
c)		agonic line
d)		aclinic lines

16. The period of oscillation of two magnets in the same field are in the ration 2:1. If their moment of inertia are equal, ratio of their magnetic moment S is

a)		1:2
b)		1:4
c)		2:1
d)		4:1

17. When a magnet is suspended horizontally at neutral point. Its frequency of oscillation is

a)		zero
b)		infinity
c)		neither of the two
d)		one

18. A dip needle which is free to move in a verticle plane $⊥ r$ to magnetic meridian will remain

a)		horizontal
b)		vertical
c)		neither horizontal nor vertical
d)		zero

19. The vertical component of earth's magnetic field is zero at

a)		magnetic equator
b)		magnetic pole
c)		geographic poles
d)		at $90^{0}$ latitude

20. The distance between the poles of a horse shoe magnet is 4cm. The pole strength of each pole is 40units. The magnetic potential midway between poles is

a)		80 units
b)		10 units
c)		20 units
d)		zero

21. Two identical coils carrying same current have common centre but have their planes at right angles to each other. If the field due to each coil is B, the resultant field will be

a)		$\sqrt{2} B$
b)		$\frac{1}{\sqrt{2}} B$
c)		2B
d)		zero

22. A bar magnet is held at right angles to a uniform magnetic field. The couple acting on the magnet is to be halved by rotating it from this position. The angle of rotation is

a)		$60^{0}$
b)		$45^{0}$
c)		$30^{0}$
d)		$75^{0}$

23. Potential at any point on equatorial line of dipole is

a)		$μ_{0} μ / 4 π d^{2}$
b)		$μ_{0} μ / 4 π d^{3}$
c)		zero
d)		none of these

24. Magnetic field intensity due to a dipole varies as $d^{h}$ where n is equal to

a)		2
b)		-2
c)		3
d)		-3

25. A cube of side $l$ is placed in a magnetic field of intensity B. The magnetic flux coming out is

a)		B $l^{2}$
b)		2B $l^{2}$
c)		6B $l^{2}$
d)		zero

26. A dip needle arranged to move freely in the magnetic meridian dips by an angle $φ$ . If the vertical plane in which the needle moves is rotated through an angle $\propto$ to the magnetic meridian, then the needle will dip by an angle

a)		$φ$
b)		$\propto$
c)		more than $φ$
d)		less than $φ$

27. With a bar magnet P in the vibration magnetometer has time period 2 seconds. When an identical bar Q of same mass and size is placed on the top of P then time period is unchanged. Which is of the following statement is true?

a)		Q is a bar magnet identical to P and similar poles of P and Q are placed together
b)		Q is not a bar magnet
c)		Q is diamagnetic bar of same dipole moment
d)		Q is a bar magnet placed with opposite poles of P and Q together

28. If a magnet is placed vertically on the horizontal board, number of neutral points orbital on the board is

a)		four
b)		one
c)		three
d)		two

29. When 3 Amp current is passed through a tangent galvanometer, it gives a deflection of $60^{0} .$ For $30^{0}$ deflection, the current must be

a)		1Amp
b)		3Amp
c)		1.5 Amp
d)		2 $\sqrt{3}$ Amp

30. The angle of dip at a place is $60^{0} .$ A magnetic needle oscillates in a horizontal plane at this place with the time period T. If the same needle is made to oscillate in a vertical plane coinciding with the magnetic meridian with a period

a)		T
b)		2T
c)		T/ $\sqrt{3}$
d)		T/2

31. At a certain place the angle of dip is $30^{0}$ and the horizontal component of earth's magnetic field is 0.50 Gauss. The earth's total magnetic field is

a)		$\sqrt{3}$
b)		1
c)		$\frac{1}{\sqrt{3}}$
d)		$\frac{1}{2}$

32. The declination at a place is $10^{0}$ west of north, The direction in which a ship should stear so that it reaches a place due east is

a)		$70^{0}$ due east
b)		$100^{0}$ due east
c)		$100^{0}$ due west
d)		$10^{0}$ due west

33. Ferromagnetising is not found in

a)		conductor
b)		semiconductor
c)		liquid and gases
d)		liquids

34. For which of the following substances, the magnetic susceptibility is independent of temperature

a)		diamagnetic
b)		ferromagnetic
c)		paramagnetic
d)		diamagnetic and ferromagnetic

35. The magnetic needle of a tangent galvonometer is deflected by an angle $30^{0}$ due to the current flowing through it. The horizontal component of earth's magnetic field 0.34 $\times 10^{- 4} T$ is along the plane of the coil. The magnetic intensity due to the current flowing is

a)		1.96 $\times 10^{- 5} T$
b)		1.96 $\times 10^{5} T$
c)		1.96 $\times 10^{- 4} T$
d)		1.96 $\times 10^{4} T$

36. A bar magnet of length 10cm and having the pole strength equal to $10^{- 3}$ weber is kept in the magnetic field having magnetic induction equal to 4 $π \times 10^{- 3} T .$ If the magnet makes an angle of $30^{0}$ with magnetic field then torque acting on the dipole is

a)		2 $π \times 10^{- 7} Nm$
b)		0.5 $\times 10^{2} Nm$
c)		2 $π \times 10^{- 5} Nm$
d)		0.5Nm

37. Relation between $\vec{H}$ , $\vec{I}$ and $\vec{B}$ is

a)		B = $μ_{0}$ (H+I)
b)		B = $μ_{0} I$
c)		B = $μ_{0}$
d)		B = $\frac{μ_{0} H}{I}$

38. A bar magnet has a magnetic moment of 5 $\times 10^{- 5}$ weber $\times metre .$ It is suspended in a magnetic field of 8 $π \times 10^{- 4} T .$ The magnet vibrates with the period of vibration equal to 15 sec. The moment of inertia of the magnet is

a)		11.25 kg $m^{2}$
b)		5.62 kg $m^{2}$
c)		0.57 kg $m^{2}$
d)		22.5 kg $m^{2}$

39. A bar magnet is suspended freely its neutral points shall lie

a)		on the axial line
b)		inside the magnet
c)		on the equational line
d)		any where around the magnet

40. A magnet used in vibration magnetometer is heated so as to reduce its magnetic moment by 19%. Then periodic time of the oscillation will

a)		Decrease by 11%
b)		Increase by 11%
c)		Decrease by 19%
d)		Decrease by 19%

41. Two identical bar magnets of dipole moment M and 2M are first placed one over another with similar poles together. The time period of oscillations is $T_{1}$ . When the polarity of one of the magnets is reversed then the time period is $T_{2}$

a)		$T_{1}$ = $T_{2}$
b)		$T_{2}$ > $T_{1}$
c)		$T_{1}$ > $T_{2}$
d)		$T_{2}$ = $\infty$

42. A circular coil carrying current I is places in earth's magnetic field such that its magnetic dipole moment is pointing towards north-west. The neutral points are located on a line passing through the centre of coil and pointing towards

a)		North
b)		East
c)		North east
d)		South east

43. The tangent galvanometer coil has radius 16 cm. When current of 40 mA is passed through it , the galvanometer shows the deflection of $45^{o}$ . If earth's horizontal components of magenetic field is 0.36x $10^{- 4} T$ then number of turns in the coil of galvanometer is

a)		220 turns
b)		225 turns
c)		229 turns
d)		235 turns

44. A bar magnet 8cm long is placed in the magnetic meridian with the N-Pole facing geographic north. Two neutral Points are seperated by a distance of 6 cms are obtained on the equitorial axis of the magnet. If
$B_{H}$ = 3.2x $10^{- 5}$ Tesla
then the pole strength of the magnet is

a)		5 ab amp.cm
b)		10 ab amp.cm
c)		20 ab amp.cm
d)		2.5 ab amp.cm

45. A dip needle in a place perpenticular to magnetic meridian will remain

a)		Vertical
b)		in any direction
c)		Horizontal
d)		At $45^{o}$ with the horz.

46. A line joining places of zero dip is called

a)		aclinic
b)		isoclinic
c)		isodynamic
d)		isogonal

47. A magnetic field of 1600 A $m^{- 1}$ produces magnetic flux of 2.4 $\times 10^{- 5}$ weber in an iron bar of cross section 0.2 ${cm}^{2}$ . THe susceptibility of iron is

a)		596
b)		1788
c)		298
d)		894

48. A point near the equator has

a)		$B_{V} ≫ B_{H}$
b)		$B_{H} ≫ B_{V}$
c)		$B_{V} = B_{H}$
d)		$B_{V} = B_{H} = 0$

49. At a place the angle of dip is $30^{0}$ . If the horisontal component of earth's field is H, then the net field intensity at the place will be

a)		H/2
b)		2H/ $\sqrt{2}$
c)		H $\sqrt{2}$
d)		H $\sqrt{3}$

50. The hysteresis cycle for a material of permanent magnet is

a)		tall and wide
b)		short and wide
c)		tall and narrow
d)		short and narrow