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Quiz 3
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Q.1
The line on the earth's surface joining the points where field is horizontal is called [ MNR 1985]
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a) magnetic meridian
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b) magnetic axis
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c)magnetic line
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d)magnetic equator
Explanation
magnetic equator the irregular imaginary line, passing round the earth near the equator, on which a magnetic needle has no dip. Answer:(d)
Q.2
The period of oscillations of a magnetic needle in a magnetic field is 1.0sec. If the length of the needle is halved by cutting it the time period will be [ MPPMT 1998]
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a) 1.0 sec
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b) 0.5 sec
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c) 0.25 sec
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d) 2.0 sec
Explanation
From the formula for period T, where I is moment of inertia, M magnetic moment, H : Horizontal component of earth's magnetic field Answer: (b)
Q.3
At magnetic poles, the angle of dip is [ CPMT 1991]
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a)45°
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b) 30°
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c)zero
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d)90°
Explanation
Answer: (d)
Q.4
When the magnet is placed vertical, neutral points obtained on the paper are [ PMT 1985]
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a) one
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b) two
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c)three
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d)four
Explanation
Answer: (a)
Q.5
For a paramagnetic material, the dependence of the magnetic susceptibility X on the absolute temperature T is given by [ Raj.PMT 1996]
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a) X ∝ T
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b) X ∝ constant ×T
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c)X ∝ (1/T)
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d)X=constant
Explanation
Answer:(c)
Q.6
A bar magnet of magnetic moment M is cut into to parts of equal length. the magnetic moment of either part is : [ CET 1994]
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a) M
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b) 2M
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c) M/2
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d) zero
Explanation
Answer: (c)
Q.7
Metals getting magnetized by orientation of atomic magnetic moments in external magnetic field is called [ EAMCET 1991]
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a)diamagnetic
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b) paramagnetic
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c)ferromagnetic
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d)antimagnetic
Explanation
Answer: (b)
Q.8
The magnetic susceptibility for diamagnetic material is [ AMU 1995]
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a)small and negative
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b) small and positive
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c)large and positive
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d)large and negative
Explanation
Answer: (a)
Q.9
At certain place the angle of dip is 30° and the horizontal component of earth's magnetic field is 0.5 oersted. The earth's total magnetic field ( in Oersted is ) [ CPMT 1990]
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a) √3
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b) 1
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c) 1 / √3
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d) 1/2
Explanation
tanθ=V/H 1 /√3=0.5/H H=0.5/√3 B=√( V2 + H2) B=1 / √3 Answer: (c)
Q.10
The temperature at and above which a ferromagnetic material becomes paramagnetic is called [ SCRA 1994]
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a)critical temperature
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b) inversion temperature
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c)curie temperature
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d)Bebye temperature
Explanation
Answer: (c)
Q.11
Which one of the following is not maid of soft iron? [ MPPMT 1995]
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a) Electromagnet
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b) core of transformer
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c)core of dynamo
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d)Magnet of loudspeaker
Explanation
Answer: (d)
Q.12
A short magnet of moment 6.75 Am2 produces a neutral point on its axis. If the horizontal component of earth's magnetic field is 5×10-5 wb/m2, then distance of the neutral point should be [ SCRA 1994]
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a) 10 cm
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b) 20 cm
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c)30 cm
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d)40 cm
Explanation
At null point magnetic field due to bar magnet=Earth's horizontal component 03 m=30 cm Answer:(c)
Q.13
Susceptibility is positive and large for [ BHU 1995]
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a) paramagnetic substance
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b) ferromagnetic substance
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c) diamagnetic substance
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d) non-magnetic substance
Explanation
Answer: (b)
Q.14
The line joining the points of zero horizontal components of earth's magnetic field is called [ MNR 1987]
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a)magnetic meridian
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b) magnetic axis
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c)magnetic line
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d)magnetic equator
Explanation
Answer: (b)
Q.15
A bar magnet of magnetic moment 104 J/T is free to rotate in a horizontal plane. the work done in rotating the magnet slowly from a direction parallel to a horizontal magnetic field of 4×10-5 T to a direction 60° from the field will be [ MPPMT 1995]
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a) 0.2 J
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b) 2.0 J
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c)4.18 J
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d)2×102 J
Explanation
W=BM ( 1 - cosθ) W=104×4×10-5 ( 1 -cosθ) W=0.2JAnswer: (a)
Q.16
Points A and B are situated perpendicular to the axis of 2 cm long bar magnet at large distance X and 3X from the centre on opposite sides. The ratio of the magnetic field at A and B will be approximately equal to : [ CPMT 1988]
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a) 1:9
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b) 2:9
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c)27:1
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d)9:1
Explanation
Magnetic field B ∝ 1 / r3 B1 / B2=(3x)3 / (x)3 Answer:(c)
Q.17
Substances which are magnetized in a magnetic field in opposite direction are called [ CPMT 1993]
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a) Diamagnetic
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b) Paramagnetic
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c) Ferromagnetic
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d) Non-magnetic
Explanation
Answer: (a)
Q.18
The time period of oscillating magnetometer is 1.5 second. The time period of oscillation of another magnet similar in size and shape, mass but having one-fourth magnetic moment than that of first magnet oscillating at the same place will be [ MPPMT 1991]
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a)0.75 sec
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b)1.5 sec
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c)3.0 sec
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d)6.0 sec
Explanation
time period T ∝ / √Mthus time period of other T' / √(M/4) ∴ T'=2T T'=2×1.5=3 secAnswer: (c)
Q.19
The work done in turning a magnet of magnetic moment 'M' by an angle of 90° from the meridian is 'n' times the corresponding done to turn it through angle of 60° where 'n' is given by [ CBSE 1995]
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a) 1/2
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b) 2
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c)1/4
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d)1
Explanation
W=MB( 1 -cosθ) W1=MB( 1- cos60)=MB/2W2=MB( 1 - cos90)=MB Given nW1=W2 n(MB/2) MB n=2 Answer: (b)
Q.20
If a dip needle is suspended at an angle of 30° to the magnetic meridian, it makes an angle of 45° with the horizontal. The real dip is [ CPMT 1998]
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a) tan-1 (√3/2)
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b) tan-1 (√3)
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c)tan-1 √(3/2)
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d)tan-1 (2 /√3)
Explanation
Let Φ be the actual deep in magnetic meridian tanΦ=V / H V=H tanΦ --(1) Vertical components are same for both the plane but horizontal component will be different tan45=V/ H' V=H'But plane of needle makes an angle with magnetic meridian of 30° thus Horizontal component in plane have component H'=H cos30 in magnetic meridian V=H cos30 --(2) from equation (1) and (2) we get H tanΦ=H cos30 tanΦ=√3 / 2 Φ=tan-1( √3 / 2) General equation can be derived as follows: Φ = is real deep in magnetic meridian= to calculate θ = is apparent or deep in geographical meridian δ = angle of declination or angle between magnetic and geographical meridian For magentic and geographical meridian verticle componant of B is same But hoorizonatl componant of B are different Thus for real deep δ V/H = tanδ Now Horizontal componant of B in geographical meridian is H' and angle betwwen magentic and geographical meridian is δ thus H' = H cosδ ---- (1) Apperent angle of deep in geographical meridian = θ V/H' = tan θ or H' = V/tanθ ---- (2) From (1) and (2) Or tan(real deep) = tan(apperent deep) cos(angle of declination) Answer:(a)
Q.21
The range of permeability of paramagnetic substance is [ Raj. PMT 1996]
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a) -1 < µ < -10
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b) 1 < µ < +10
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c) 1 < µ > 10
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d) 0 < µ < 1
Explanation
Answer: (b)
Q.22
A magnet of magnetic moment M is rotated through 360° in a magnetic field H, the work done will be [ MPPMT 1994]
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a)MH
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b) 2MH
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c)2πMH
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d)zero
Explanation
Answer: (d)
Q.23
Electromagnets are made of soft iron, because soft iron has [ MNR 1988]
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a) low susceptibility and low retentivity
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b) high susceptibility and low retentivity
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c)high susceptibility and high retentivity
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d)low permeability and high retentivity
Explanation
Answer: (b)
Q.24
The angle of dip at a place on the earth gives ..[ MPPET 1994]
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a) the horizontal component of the earth's magnetic field
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b) the location of the geographic meridian
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c)the vertical component of the earth's field
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d)the direction of the earth's magnetic field
Explanation
Answer:(d)
Q.25
Magnetic lines of force due to a bar magnet do not intersect because [ PMT 1995]
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a) a point always has a single net magnetic field
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b) line have similar charges and so repel each other
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c) the lines always diverge from a single point
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d) the line need magnetic lenses to be made to intersect
Explanation
Answer: (a)
Q.26
The earth's magnetic field at a certain place has a horizontal component 0.3 Gauss and the total strength 0.5 gauss. The angle of dip is [ MPPMT 1995]
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c)tan-1 (4/3)
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a)tan-1 (3/4)
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b) sin-1 (3/4)
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d)sin-1 (3/5)
Explanation
B2=V2 + H2 tanθ=V/HAnswer: (c)
Q.27
Point A and B are situated along the extended axis of 2cm long bar magnet at a distance x and 2x respectively from the pole nearer to the points. the ratio of the magnetic field at A and B will be [ CPMT 1986]
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a) 4:1 exactly
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b) 4:1 approximately
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c)8:1 exactly
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d)8:1 approximately
Explanation
since bar magnet length is small compared to x . thus ratio will be approximateB ∝ (1/x3)B' ∝ 1/(2x3)Thus B:B'=8:1Answer: (d)
Q.28
Using a bar magnet P, a vibration magnetometer has time period of 2seconds. When a bar Q ( identical to P in mass and size) is placed on the top of P, the time period is unchanged. Which of the following statements is true] [ PMT 1995]
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a) Q is non-magnetic material
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b) Q is a bar magnet identical to P, and its north pole is placed on top of P's north pole
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c)Q is of unmagnetized ferromagnetic material
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d)Nothing can be said about Q's properties
Explanation
Answer:(b)
Q.29
A bar magnet has a magnetic moment equal to 5×10-5 weber×metre. It is suspended in a magnetic field which has a magnetic induction (B) equal to 8π×10-4 tesla. The magnet vibrates with period of vibration equal to 15 seconds. the moment of inertia of the magnet is [ MPPMT 1993]
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a) 22.5 kg×m2
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b) 11.25 kg×m2
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c) 5.62 kg×m2
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d) 7.16×10-7 kg×m2
Explanation
From the formula for time period solve equation of I Answer: (d)
Q.30
At a place the angle of dip is 30°. If the horizontal component earth's field is H, then the total field intensity will be given by: [ MNR 1993]
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a) H / 2
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b) 2H / √3
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c)H√2
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d)H√3
Explanation
B2=V2 + H2tanθ=V / H V=Htanθ B2=V2 + H2 solving above equation Answer: (b)
0 h : 0 m : 1 s
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