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Q.1
Domain formation is the necessary feature of ..... [ GUJCET 2007]
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a) ferromagnetism
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b) paramagnetism
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c) diamagnetism
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d) All of these
Explanation
Answer: (a)
Q.2
A steel wire of length l has a magnetic moment M. It is then bent into a semicircular arc. the new magnetic moment is [ BHU 1995]
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a) M
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b) 2M /π
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c)M/l
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d)M×l
Explanation
Answer: (b)
Q.3
A bar magnet of magnetic moment 200 Am2 suspended in a magnetic field of intensity 0.25 N/Am. The couple required to deflect it through 30° is .. [ AFMC 2011]
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a) 15Nm
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b) 30Nm
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c) 25Nm
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d) 45Nm
Explanation
Torque acting on the bar magnet is τ=MH sin θ τ=200 ×0.25 × sin 30° τ=25Nm Answer: (c)
Q.4
If a diamagnetic substance is brought near the north or south pole of a bar magnet, is ... [ CBSE-PMT 2009]
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a) repelled by the north pole and attracted by the south pole
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b) attracted by the north and repelled by the south pole
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c) attracted by both the poles
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d) repelled by both the poles
Explanation
Diamagnetic substance are repelled by external magnetic field Answer: (d)
Q.5
Current 'i' is flowing in a coil of area and number of turns N, then magnetic moment of the coil, M is ... [ CBSE-PMT 2001]
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a)NiA
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b) Ni /A
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c)Ni/ √A
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d)N2Ai
Explanation
Magnetic moment linked with one turn=iA. here A is area of current loopMagnetic moment linked with N turns=iNA amp-m2 .Answer: (a)
Q.6
The magnetic moment of a diamagnetic atom is ... [ CBSE-PMT 2010]
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a) equal to zero
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b) much greater than one
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c)1
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d)between zero and one
Explanation
Answer: (a)
Q.7
Above Curie temperature... [ CBSE-PMT 2006]
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a) a paramagnetic substance becomes diamagnetic
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b) a diamagnetic substance becomes paramagnetic
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c)a paramagnetic substance becomes ferromagnetic
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d)a ferromagnetic substance becomes paramagnetic.
Explanation
Above Curie temperature, a ferromagnetic substance becomes paramagnetic Answer:(d)
Q.8
A short bar magnet of magnetic moment 0.4JT-1 is placed in a uniform magnetic field of 0.16T. The magnet is in stable equilibrium when the potential energy is ... [ CBSE-PMT 2011]
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a)-0.64J
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b) zero
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c)-0.082J
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d) -0.064J
Explanation
For stable equilibrium θ=0U=-MBU=-(0.4)(0.16) U=-0.064JAnswer: (d)
Q.9
For protecting a sensitive equipment from the external electric arc, it should be... [ CBSE-PMT 1998]
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a) wrapped with insulation around it when a current is passing through it.
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b) placed inside an iron can
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c)surrounded with fine copper sheet
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d)placed inside the aluminum can
Explanation
The iron can produces a magnetic screening for the equipment as line of magnetic force can not enter iron enclosureAnswer: (b)
Q.10
bar magnet of magnetic moment 200 A-m2 is suspended in a magnetic field of intensity 0.25N/Am. The couple required to deflect it through 30° is ...[ AFMC 1999]
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a)15 N-m
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b) 20N-m
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c)25 N-m
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d)50 N-m
Explanation
torque=MB sinθ torque==(200) (0.25) sin30 torque=25 N-mAnswer: (c)
Q.11
If the magnetic dipole is rotated through the angle θ with respect to the direction of H, then work done will be..[ AFMC 1997]
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a) MH(1-cosθ)
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b) MH cosθ
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c)MH(1-sinθ)
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d)MH sinΘ
Explanation
Torque on magnetic dipole τ=MHSinθhere θ is angle between M and H ( horizontal component of earth's magnetic fieldLet dipole rotated through small angle dθWork done by external agency dw=MHSinθdθ --eq(1)If dipole is rotated by θ from its equilibrium position 0° then work done by external agency can be obtained by integrating equation(1) from 0° to θAnswer: (a)
Q.12
A diamagnetic substance is placed in a magnetic field of a bar magnet Then it is ...[ AFMC 2003]
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a) repelled by magnet
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b) attracted by magnet
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c)attracted by S-pole and repelled by N-pole
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d)attracted by S-pole and repelled by N-pole
Explanation
When diamagnetic substance is placed in magnetic field of bar magnet then magnetic field is induced in diamagnetic substance in such direction which will respell external magnetic field. Thus It goes from region of higher magnetic field to lower magnetic field Answer:(a)
Q.13
At which place, earth's magnetic field becomes horizontal? [ AFMC 2004]
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a) Magnetic pole
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b) Geographical pole
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c) Magnetic meridian
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d) Magnetic equator
Explanation
The magnetic meridian is an equivalent imaginary line connecting the magnetic south and north poles and can be taken as the horizontal component of magnetic force lines along the surface of the earth. Therefore, a compass needle will be parallel to the magnetic meridian.Answer: (c)
Q.14
The substances in which the magnetic moment of a single atom is not zero, is called as [ AFMC 1999]
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a)ferromagnetic
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b) paramagnetic
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c)ferromagnetic
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d)diamagnetic
Explanation
In paramagnetic substance resultant magnetic moment is zero, but all atoms have some magnetic momentAnswer: (b)
Q.15
At a certain place, the horizontal component of earth's magnetic field is √3 time of its vertical component, the angle of dip at that place is .. [ AFMC 2000]
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a) 75°
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b) 60°
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c)45°
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d)30°
Explanation
Given H=V√3tanδ=V/H=1 / √3 ∴ δ=30°Answer: (d)
Q.16
Curie temperature of iron is the temperature below which it is ...[ AFMC 2002]
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a) super conducting
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b) ferromagnetic
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c)diamagnetic
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d)radioactive
Explanation
Curie temperature is the temperature beyond which ferromagnetic substance becomes paramagnetic. So below this temperature iron will be ferromagnetic Answer:(b)
Q.17
The work done in turning a magnetic moment M by an angle of 90° from the meridian is an times the corresponding work done to turn through an angle of 60°, where an is given by .. [ AFMC 2002]
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a) 1
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b) 1/2
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c) 4
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d) 2
Explanation
Formula for work done=MB(1-cosθ) First case θ=90° W1=MB ( 1-cos90)=MB Second case θ=60° W2=MB ( 1- cos60)=MB (1/2) Given that W1 / W2 =n MB / (½MB)=2 Thus n=2 Answer: (d)
Q.18
) In which type of material the magnetic susceptibility does not depend on temperature [ AFMC 2007]
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a)diamagnetic
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b) paramagnetic
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c)Ferromagnetic
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d)Ferrite
Explanation
Diamagnetic materials have negative susceptibility. So, it does not depends on temperatureAnswer: (a)
Q.19
Angle between magnetic meridian and geographical meridian is called..[ AFMC 2009]
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a) angle of dip
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b) angle of declination
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c)angle of depression
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d)both(a) and (b)
Explanation
Angle between magnetic meridian and geographical meridian is called angle of declinationAnswer: (b)
Q.20
The magnetic lines of forces inside a bar magnet.. [ AFMC 2009]
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a) are from north pole to south pole of the magnet
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b) do not exist
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c)depend upon the area of cross-section of bar magnet
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d)are from south pole to north pole of the magnet
Explanation
Magnetic field lines direct from North to South pole out side the magnet but from South to North inside the bar magnet. Answer:(d)
Q.21
The angle of dip is θ at a place where the horizontal and vertical component of the earth's magnetic field is equal. The value of θ is : [ SCRA 1994]
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a) 0°
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b) 30°
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c)45°
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d)60°
Explanation
tanθ=V/H Answer:(c)
Q.22
Nickel shows ferromagnetic property at room temperature. if the temperature is increased beyond Curie temperature, then it will show... [ CBSE-PMT 2007]
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a) anti ferromagnetism
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b) no magnetic property
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c)diamagnetism
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d)para magnetism
Explanation
Beyond Curie temperature, ferromagnetic substance behave like paramagnetic substance Answer:(d)
Q.23
If the magnetic dipole moment of an atom of diamagnetic material and ferromagnetic material are denoted by µd, µp, µf respectively, then ... [ CSBE-PMT 2005]
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a) µd=0 andµp ≠ µp
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b) µd ≠ 0 andµp=0
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c) µp=0 andµf ≠ 0
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d) µd ≠ 0 and µf ≠ 0
Explanation
The magnetic dipole moment of diamagnetic material is zero as each of its pair of electrons have opposite spins i.e µd=0 Paramagnetic substance have dipole moment > 0, i.e µp ≠ 0 Ferro-magnetic substance are very strong magnetic moment i.e µf ≠ 0 Answer: (a)
Q.24
Electromagnets are made of soft iron because soft iron have ... [ CBSE-PMT 2010]
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a)low retentivity and high coercivity
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b) high retentivity and high coercivity
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c)low retentivity and low coercivity
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d)high retentivity and low coercivity
Explanation
At applied magetic filed H = 0, B ≠ 0. The value of B at H = 0 is called retentivity or remanence. The value of the magnetizing field H which has to be applied to the magnetic material in the reverse direction so as to reduce its residual magnetism to zero is called its coercivity. At H ≠ 0, B = 0. The value of H at B = 0 is called coercivity. Material used for making an electromagnet has to undergo cyclic changes. Therefore, the ideal material for making an electromagnet has to be one which has the least hysteresis loss. Moreover, the material should attain high values of magnetic induction B at low values of magnetizing field H. Soft iron is preferred for making electromagnets as it has a thin hysteresis loop[small area, therefore less hysteresis loss] and low retentivity.It attains high values of B at low values of magnetizing field. Answer: (c)
Q.25
A vibrating magnetometer placed in magnetic meridian has a small bar magnet. The magnet executes oscillations with time period of 2 sec in earth's horizontal magnetic field of 24 microtesla.When a horizontal field of 6 microtesla is produced opposite to the earth's field by placing a current carrying wire, the new time period of magnet will be ...[ CBSE-PMT 2010]
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a) 1 s
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b) 2s
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c)3s
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d)4s
Explanation
Time period of vibration magnetometerAnswer: (d)
Q.26
There are four light-weight rod samples A,B,C,D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted.. [ CBSE-PMT 2011] (i) A is freely repelled(ii) B is feebly attracted(iii) C is strongly attracted(iv) D remains unaffectedWhich one of the following is true?
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a) B is of a paramagnetic material
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b) C is of a diamagnetic material
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c)D is of a ferromagnetic material
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d)A is of a non-magnetic material
Explanation
A=diamagnetic B=ParamagneticC=FerromagneticD=Non magnetic Answer:(a)
Q.27
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 quadrupled [ CBSE-PMT 1994]
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a) motion remains simple harmonic with new period=T/2
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b) motion remains simple harmonic with new period=2T
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c) motion remains simple harmonic with new period=4T
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d) motion remains simple harmonic and the period stays nearly constant
Explanation
The time periode of a br magnet in a magnetic field is given by Here I=moment of inertia, M=moment of magnet, B=magnetic fieldT ∝ √ I ∝ √mSo T becomes twice when mass becomes four times Answer: (b)
Q.28
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 .. [ CBSE-PMT 1995]
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a)2
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b) 1
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c)0.5
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d)0.25
Explanation
Work done to rotate dipole by an angle of 90°from magnetic meridian is given by W1=MB ( cos 0 - cos90) W1=MB (1-0) MB Work done to rotate dipole by an angle of 60°from magnetic meridian is given byW2=MB ( cos 0 - cos60) W2=MB (1- ½ )=MB/2 Given that W1=2 W2 Thus n=2Answer: (a)
Q.29
If a diamagnetic substance is brought near north or south pole of a bar magnet, it is ... [ CBSE-PMT 1999]
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a) attracted by the poles
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b) repelled by the poles
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c)repelled by north pole and attracted by the south pole
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d)attracted by the north pole and repelled by the south pole
Explanation
Diamagnetic substance dont have any unpaired electron, They are magnetized in direction opposite to that of magnetic field. Hence, when they are brought to north or south pole of a bar magnet, they are repelled by polesAnswer: (b)
Q.30
A bar magnet, of magnetic moment M , is placed in magnetic field of induction B. The torque exerted on it is ... [ CBSE-PMT 1999]
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a) M ⋅ B
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b) -M ⋅ B
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c)M × B
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d)B × M
Explanation
Answer:(c)
0 h : 0 m : 1 s
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