chapter 5 magnetism and matter class 12 important questions pdf
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Q.(1)- Stable magnets are made of steed but electromagnets are made of soft irons. Why?
But coercivity of soft iron is low and magnetic susceptibility (or permeability) of soft iron is high so electromagnets are made of soft iron.
Q.(2)- Write two difference between electromagnet and permanent magnet.
Bihar Board - 2012 , 2020
Answer- Electromagnet -
(i) Electromagnets are made of soft ferromagnetic material. e.g.- soft iron.
(ii) It has a temporary magnetic field, which last as long as the
current flows through its coils.
Permanent magnet-
(i) Permanent magnets are made of hard ferromagnetic
materials. e.g.- Steel.
(ii) It has a permanent magnetic field.
Q.(3)-State two characteristics properties distinguishing the behavior of
paramagnetic and diamagnetic materials.
Bihar Board - 2014
Answer- Paramagnetic materials -
(i) Paramagnetic materials are feebly attracted by a magnet.
(ii) Magnetic susceptibility of a paramagnetic material is positive but very
small.
Diamagnetic materials -
(i) Diamagnetic materials are feebly repelled by a magnet.
(ii) Magnetic susceptibility of a diamagnetic material is negative but very small.
Q.(4)-A uniform magnetic field gets modified as shown in the figure , when two
specimens X and Y are placed in it .
(i) Identity the two specimen X and Y.
(ii) State the reason for modification of the field lines in X and y.
Bihar Board - 2009
Answer- (i) Specimen X is a diamagnetic material and specimen Y is a
ferromagnetic material.
(ii) Relative permeability of a diamagnetic material is less than 1, so magnetic field lines are repelled by a diamagnetic material .
But relative permeability of a ferromagnetic is (far) greater
than 1 , so magnetic field lines are attracted by a ferromagnetic material .
Q.(5)- Explain end-on position and broad side-on position of a bar magnet.
Bihar Board - 2020
Answer- End-on position - Any point on the line joining the north-south pole of a
magnet is called end-on position .
Broad side-on position - Any point on the line passing through center and
perpendicular to axis of the bar magnet is called broad-on position .
Q.(6)- Write expression for magnetic field B on axis and equator of a short bar magnet .
Bihar Board - 2017
Answer- Magnetic field due to a short bar magnet at a point on the axis .
\[{{B}_{axial}}=\frac{{{\mu
}_{0}}}{4\pi }\times \frac{2M}{{{r}^{3}}}\]
Magnetic field due to a short bar magnet at a point on the equator .
\[{{B}_{equatorial}}=\frac{{{\mu }_{0}}}{4\pi }\times \frac{M}{{{r}^{3}}}\]
Where M= magnetic dipole moment of the short bar magnet
r= distance of the point from the center of the bar magnet
Answer- 
Magnetic dipole moment of a bar-magnet 
M = m × 2l ------ (i)
If a bar magnet is cut perpendicular to its length, pole-strength will be unchanged but its length becomes half .
If a bar magnet is cut perpendicular to its length, pole-strength will be unchanged but its length becomes half .
M = m × l -------(ii)
If bar magnet is cut parallel to its length then length will be unchanged but pole strength becomes half.
If bar magnet is cut parallel to its length then length will be unchanged but pole strength becomes half.
M = m/2 × 2l = ml ----(iii)
from (i),(ii),(iii)
In both cases, Magnetic dipole moment will be half of the original value of dipole moment of the bar magnet.
from (i),(ii),(iii)
In both cases, Magnetic dipole moment will be half of the original value of dipole moment of the bar magnet.
Q.(8)- Explain the process of demagnetization.
Answer- When atomic magnets of a material are align in a direction then material has some net dipole moment. Hence material is magnetized.
When material is heated or beaten alignment of atomic magnets are disturbed. Due to which net dipole moment of the material becomes zero i.e. the material is demagnetized.Q.(9)-What is navigation (Mariner’s) compass?
Answer- This is an instrument, which is used to find direction.
This instrument has a horizontal aluminum dial at the pilot of a semi-spherical bowl. There are eight magnetic needles are set on the pilot so that they can rotate with the dial in horizontal plane.
Different compass points are printed on the dial to indicate direction.
Q.(10)- What is hysteresis and coercive force?
Answer- Hysteresis- Lagging of magnetic induction field (B) behind magnetizing field (H) is called hysteresis.
Answer- Hysteresis- Lagging of magnetic induction field (B) behind magnetizing field (H) is called hysteresis.
Coercive force- Magnetic field required to destroy residual magnetic field is called coercive force.
Q.(11)- What is a hysteresis loop ? with its help explain the term retentivity and
coercivity.
Bihar Board - 2010
Answer- Hysteresis loop- B– H (magnetic induction field – magnetizing field) graph for a
cycle of magnetization (of a ferromagnetic material) is called hysteresis loop.
When magnetizing field and magnetic induction field changes from zero to maximum in one direction then changes from maximum to zero in opposite direction then some amount of magnetic induction field remains in the specimen at zero value of magnetizing field. This magnetic field is called retentivity or residual magnetism (Br) or remanence .
To destroy residual magnetism we apply magnetizing field in opposite direction ,which is called coercive force (Hc) or coercivity.
Retentivity- Magnetic field remained inside a ferromagnetic material
after removal of external (applied) magnetic field is called retentivity.
Coercivity- Magnetic field required to destroy residual magnetism is
called coercivity .
Q.(12)- What do you mean by magnetic elements of the earth ?
Bihar Board - 2020
Answer- Read in Nawendu Physics Classes notes.
Q.(13)- What do you mean by neutral points?
Answer- The points in the magnetic field of a magnet where resultant of (horizontal component of ) earth magnetic field and magnetic field of magnet is zero, are called neutral points.
Q.(14)-However is the net dipole moment obtained if two magnets are combined?
Q.(14)-However is the net dipole moment obtained if two magnets are combined?
Answer- Since dipole moment is a vector quantity hence net value of dipole moment is obtained from law of addition of vectors .
Net dipole moment =\[M=\sqrt{M_{1}^{2}+M_{2}^{2}+2{{M}_{1}}{{M}_{2}}\cos
\theta }\]
case-(i) when $\theta ={{0}^{\circ
}}$
$M={{M}_{1}}+{{M}_{2}}$
case-(ii) when $\theta ={{90}^{\circ }}$
$M=\sqrt{M_{1}^{2}+M_{2}^{2}}$
case-(iii) when $\theta ={{180}^{\circ }}$
$M={{M}_{1}}-{{M}_{2}}$
Q.(15)- Repulsion is the real identity of magnetism, how?
Answer- Like magnetic poles repel each other and unlike magnetic poles attract each other. But magnet and iron only attract each other. Therefore, the real identity of magnetism is repulsion.
Q.(16)- What do you mean by apparent angle of dip at any place ?
Bihar Board - 2021,2022
Answer- The angle of dip in any other meridian except magnetic meridian is called apparent angle of dip .
The actual dip (which is measured in magnetic meridian)= \[\delta \]
The apparent dip (which is measured in any other meridian)= \[{{\delta }^{'}}\]
The angle between magnetic meridian and the other meridian= $\theta $
then, $\tan \delta
'=\frac{\tan \delta }{\cos \theta }$
Q.(17)- What do you mean by end-on position of a magnet ?
Bihar Board - 2022
Answer- End-on position - Any point on the line joining the north-south pole of a magnet is called end-on position .
Q.(18)- Write the definition of angle of dip.
Bihar Board - 2022
Answer- Angle between earth's magnetic field and horizontal direction of magnetic meridian is called angle of dip.
* It is denoted by $\delta $.
Q.(19)- Explain magnetic moment .
Bihar Board - 2022
Answer- For a current loop-
Product of ampere turn and area is called magnetic (dipole) moment.
M= NI x A
For a bar magnet-
Product of magnitude of pole strength of any of the poles of a (small) bar magnet and the distance between the poles is called magnetic moment.
M=m x 2l
* SI unit of magnetic moment is $A{{m}^{2}}$ or J/T .
* Magnetic moment is a vector quantity . Which is directed from south pole to north pole.
Q.(20)- Write down the definition and SI unit of magnetic flux .
Bihar Board - 2022
Answer- Magnetic flux - Dot product of magnetic induction field and area vector is called magnetic flux.
* It is denoted by $\varphi $.
* It is a scalar quantity.
$\varphi
=\vec{B}.\vec{A}=BA\cos \theta $
where $\theta $= angle between $\vec{B}$and$\vec{A}$
S.I. unit-
Magnetic flux= magnetic induction field x area
= tesla x ${{\left( meter \right)}^{2}}$
= weber
= Wb
SI unit of magnetic flux is $tesla{{(meter)}^{2}}$ . Which is called weber (Wb) .
chapter 1 ELECTRIC CHARGES AND FIELDS short Q-A
chapter 2 ELECTROSTATIC POTENTIAL AND CAPACITANCE short Q-A
chapter 3 CURRENT ELECTRICITY short Q-A
chapter 4 MOVING CHARGES AND MAGNETISM short Q-A
chapter 6 ELECTROMAGNETIC INDUCTION short Q-A
chapter 7 ALTERNATING CURRENT short Q-A
chapter 8 ELECTROMAGNETIC WAVES short Q-A
chapter 2 ELECTROSTATIC POTENTIAL AND CAPACITANCE short Q-A
chapter 3 CURRENT ELECTRICITY short Q-A
chapter 4 MOVING CHARGES AND MAGNETISM short Q-A
chapter 6 ELECTROMAGNETIC INDUCTION short Q-A
chapter 7 ALTERNATING CURRENT short Q-A
chapter 8 ELECTROMAGNETIC WAVES short Q-A
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