Magnetic Materials & Magnets Test

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Magnetic Materials & Magnets Test - 5

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Weekly Quiz Competition

Question 1
1 / -0.25

When iron filings are sprinkled on a sheet of glass placed over a short bar magnet then,

A
The iron filings form a pattern of suggesting that the magnet has north pole similar to the positive charge

B
The iron filings form a random pattern of suggesting that the magnet has random pole

C
The iron filings form a pattern suggesting that the magnet has two poles similar to the positive and negative charge of an electric dipole

D
The iron filings form a pattern of suggesting that the magnet has south pole similar to the negative charge

Solution

Explanation:North pole act as positive end and South pole act as negative end. The iron fillings in the presence of magnetic field gets magnetized and form a tiny magnet which then gets attracted to the poles of bar magnet. North pole of bar magnet attracts south pole of tiny magnet and vice-versa. So all the iron fillings are arranged as the magnetic field lines of bar magnet.
Question 2
1 / -0.25

Diamagnetic substances are

A
those which have tendency to move from stronger to the weaker part of the external magnetic field

B
those that are uneffected by external magnetic fields

C
those that develop a net magnetic moment in direction of applied field

D
those which have tendency to move from weaker to the stronger part of the external magnetic field

Solution

When a diamagnetic material is placed in an external magnetic field the spin motion of electrons is so modified that the electrons which produce the moments in the direction of the external field show down while the electrons which produce magnetic moments in opposite directions get accelerated.
Thus, a net magnetic moment is induced in the opposite direction of the applied magnetic field. Hence the substance is magnetized opposite of the external field. Thus, it moves from stronger. Weaker parts of the magnetic.
Question 3
1 / -0.25

A cube-shaped permanent magnet is made of a ferromagnetic material with a magnetization 8 * 10⁵ M of about The side length is 2 cm. Magnetic field due to the magnet at a point 10 cm from the magnet along its axis is

A
0.003 T

B
0.002 T

C
0.004 T

D
0.001 T

Solution

Correct Answer :- d

Explanation : μ_total = MV

= (8*10⁵ )(2*10^-2 )

= 6A m²

Magnetic field on the axis of a current loop with magnetic material μtotal is:

B = μ₀ μ_total / (2 π(x² + a² )^1/2

B = (4 π*10^-7 )(6) / [2 π(0.1)]

= 1 * 10^-3 T

= 0.001 T
Question 4
1 / -0.25

A bar magnet of magnetic moment 1.5 J/T lies parallel to the direction of a uniform magnetic field of 0.22 T. What is the torque acting on it?

A
-0.3J

B
0.0J

C
0.23J

D
0.3J

Solution

Answer :-

Solution :- torque when =180 °

= 1.5 ×0.22 ×sin 180 °

= 0.33 ×0 = 0 Nm
Question 5
1 / -0.25

A short bar magnet of magnetic moment 5.25 ×10⁻² JT⁻¹ is placed with its axis perpendicular to the earth ’s field direction. At what distance from the centre of the magnet, the resultant field is inclined at 45 with earth ’s field on its normal bisector . Magnitude of the earth ’s field at the place is given to be 0.42 G. Ignore the length of the magnet in comparison to the distances involved.

A
5.5 cm

B
7.0 cm

C
6.0 cm

D
5 cm

Solution

According to the question, the resultant field is inclined at 45o with earth 's magnetic field.
tan θ=B_H /B
θ=45^o
tan θ=1=B_H /B
B_H =B= μ_o M /4 πr³
Given, B= 0.42 ×10⁻⁴ T
M=5.25 ×10⁻² J/T
Therefore,0.42+10⁻⁴ =10⁻⁷ ×[(5.25 ×10⁻² )/r³ ]
r³ =12.5 ×10⁻⁵ =125 ×10⁻⁶
r=5 ×10⁻² m = 5 cm
Question 6
1 / -0.25

Which of the following statements about magnetic field lines true?

A
The magnetic field lines of a magnet (or a solenoid) form continuous closed loops

B
The smaller the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B.

C
The perpendicular to the field line at a given point gives direction of magnetic field

D
The larger the number of field lines crossing per unit area, the weaker is the magnitude of the magnetic field B.

Solution

Magnetic poles exist in pairs. It is not possible to isolate a north pole or a south pole. Magnetic field lines start from the north pole and go to the south pole and return to the north pole. They form continuous closed loops unlike electric lines of force which do not as an electric monopole, a single charge does exist.
Question 7
1 / -0.25

For diamagnetic materials

A
additional field caused by atoms is always parallel in direction to that of the external field

B
additional field caused by atoms is always perpendicular in direction to that of the external field

C
additional field caused by atoms is always in same direction as that of the external field

D
additional field caused by atoms is always opposite in direction to that of the external field

Solution

It is because when we make a group of electrons inside the material it is called domain. So when we apply an external magnetic field on the material. Those domains start to align themselves in the direction of the magnetic field. BUT NOT ALL DOMAINS ALIGN THEMSELVES IN THAT DIRECTION. So option D is correct.
Question 8
1 / -0.25

permeability of a paramagnetic material is expected to decrease with increasing temperature because

A
random thermal motion increases magnetic moment alignment

B
electrons stop moving

C
electrons go into forbidden gap

D
random thermal motion reduces magnetic moment alignment

Solution

When a parametric material comes close to a magnetic field the atoms will align with the magnetic field which causes another magnetic field. Permeability is the total magnetic field divided by the original magnetic field. Increase in temperature makes it harder for the atoms to align which decreases the strength of the second field. This results in a lower total magnetic field (numerator) and thus lower permeability.
Question 9
1 / -0.25

A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its north tip pointing down at 220 with the horizontal. The horizontal component of the earth ’s magnetic field at the place is known to be 0.35 G. Determine the magnitude of the earth ’s magnetic field at the place.

A
0.48G

B
0.28G

C
0.58G

D
0.38G

Solution

We know the horizontal component of earth magnetic field H=R cos θ
Where θ=angle of dip=22⁰ and the value of H=0.35G
So, putting the values respectively R= H/cos θ=0.35/cos22=0.35/0.927=0.377=0.38G
Question 10
1 / -0.25

A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnetic field B in the core for a magnetising current of 12 A ?

A
4.48 T

B
5.48 T

C
44.8 T

D
48 T

Solution

Given data,
Rowland ring is toroid with a core of magnetic material,
Radius of the ring r=15cm
Number of turns of the wire N=3500
Relative permeability of the core,μ_r =800
Magnetising current, I=1.2A
Magnetic field, B=?
Using the formula for the magnetic field of a toroid,
B=μ₀ nI
Number of turns per unit length, n=N/2 πr=3500/(2 π×15 ×10⁻² )
Therefore,
B=μ₀ μ_r nI
The magnetic field is given by the relation,
B= μr μ0 IN /2 πr
= (800 ×4 π×10⁻⁷ ×1.2 ×3500)/2 π×0.15 =4.48T

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Magnetic Materials & Magnets Test - 5

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Question 1

The iron filings form a pattern of suggesting that the magnet has north pole similar to the positive charge

The iron filings form a random pattern of suggesting that the magnet has random pole

The iron filings form a pattern suggesting that the magnet has two poles similar to the positive and negative charge of an electric dipole

The iron filings form a pattern of suggesting that the magnet has south pole similar to the negative charge

Solution

Question 2

those which have tendency to move from stronger to the weaker part of the external magnetic field

those that are uneffected by external magnetic fields

those that develop a net magnetic moment in direction of applied field

those which have tendency to move from weaker to the stronger part of the external magnetic field

Solution

Question 3

0.003 T

0.002 T

0.004 T

0.001 T

Solution

Question 4

-0.3J

0.0J

0.23J

0.3J

Solution

Question 5

5.5 cm

7.0 cm

6.0 cm

5 cm

Solution

Question 6

The magnetic field lines of a magnet (or a solenoid) form continuous closed loops

The smaller the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B.

The perpendicular to the field line at a given point gives direction of magnetic field

The larger the number of field lines crossing per unit area, the weaker is the magnitude of the magnetic field B.

Solution

Question 7

additional field caused by atoms is always parallel in direction to that of the external field

additional field caused by atoms is always perpendicular in direction to that of the external field

additional field caused by atoms is always in same direction as that of the external field

additional field caused by atoms is always opposite in direction to that of the external field

Solution

Question 8

random thermal motion increases magnetic moment alignment

electrons stop moving

electrons go into forbidden gap

random thermal motion reduces magnetic moment alignment

Solution

Question 9

0.48G

0.28G

0.58G

0.38G

Solution

Question 10

4.48 T

5.48 T

44.8 T

48 T

Solution

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