Magnetism and Matter Test -6

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Magnetism and Matter Test -6

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Weekly Quiz Competition

Question 1
1 / -0

In Ferromagnetic materials

A
strong interactions between atomic magnetic moments cause them to line up parallel to each other in regions called magnetic domains even if there is no external field

B
atomic magnetic moments are random in strong external fields

C
weak interactions between atomic magnetic moments cause them to line up anti parallel to each other in external field

D
strong interactions between atomic magnetic moments cause them to line up anti parallel to each other in external field

Solution

In the absence of external magnetic field individual atom/ion/molecule align themselves in common direction over a macroscopic volume called domain. But the net dipole moment of entire specimen is zero as directions of dipole moments of these domains are random. But in presence of external magnetic field, the domains orient themselves in direction of external magnetic field and possess net dipole moment in direction of external magnetic field.
Question 2
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Permanent magnets should have

A
low retentivity and high coercivity

B
low retentivity and low coercivity

C
high retentivity and low coercivity

D
high retentivity and high coercivity

Solution

The material should have high retentivity so that the magnet is strong and high coercivity so that magnetization is not erased by stray magnetic fields, temperature fluctuations or minor mechanical damage.
Question 3
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For strong electromagnets, core is made of

A
paramagnetic substance

B
soft ferromagnetic substance

C
diamagnetic substance

D
air

Solution

Ferromagnetic substances get magnetized strongly in the presence of a magnetic field. Further due to low coercivity it gets easily demagnetize. Also, hysteresis losses are less.
Question 4
1 / -0

The angle of dip at a location in southern India is about 18^o. Dip angle in Britain would be

A
18^o

B
greater

C
0^o

D
smaller

Solution

We expect a greater angle becuase it is located close to north pole.
Question 5
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If you made a map of magnetic field lines at Melbourne in Australia, would the lines go into the ground or come out of the ground?

A
Lines seem to come out at 45 degrees to the ground

B
Lines seem to come out of the ground

C
Lines seem to be horizontal to the ground

D
Lines seem to go into the ground

Solution

Magnetic field lines seem to come out of the ground, because magnetic feild lines emerges from magnetic North pole that lies in the Southern Hemisphere. Australia is near the magnetic north pole so, magnetic field lines will seem to be emerging.
Question 6
1 / -0

To increase the magnetic field of a solenoid what core material should be used?

A
Ferromagnetic material

B
Insulating material

C
Paramagnetic material

D
Diamagnetic material

Solution

Ferromagnetic substances get strongly magnetized by magnetic field. The relative permeability of ferromagnetic substances is very high, of the order of 1000.
Question 7
1 / -0

If the area under the B-H curve of a material M is more, in an ac solenoid using material M

A
heat generated is very low

B
more heat is generated

C
heat generated is ultra low

D
no heat is generated

Solution

more heat is generated because heat produced per unit volume per cycle is equal to area of hysterisis loop (B - H curve).
Question 8
1 / -0

If we wanted to cancel the Earth’s magnetic field by running an enormous current loop around the equator, which way would the current have to flow: or west to east?

A
south to north

B
east to west

C
west to east

D
north to south

Solution

The lines of the Earth’s magnetic field enter the planet in Hudson Bay and emerge from Antarctica; thus, the field lines resulting from the current would have to go in the opposite direction.
Question 9
1 / -0

Assuming one unpaired electron spin per atom, saturation magnetization in a long cylinder of iron is(n for iron is 8.6 × 10²⁸atoms/m³,Bohr magneton = 9.27 × 10⁻²⁴J/T)

A
7.0 × 10⁵A/m

B
6.0 × 10⁵A/m

C
9.0 × 10⁵A/m

D
8.0 × 10⁵A/m

Solution

Saturation magnetization = n × Bohr magneton
= 7.97 × 10⁵ A/m = 8 × 10⁵ A/m (approx)
Question 10
1 / -0

The strength of magnetic field around a bar magnet :

A
decrease with the decrease in distance from the magnet

B
decrease with the increase in distance from the magnet

C
remain constant with increase in distance from magnet

D
becomes zero with decrease in distance from magnet

Solution

The strength of magnetic field due to a bar magnet is strong near the magnet and it gets weaker as distance is increased.
Question 11
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The hysterisis curve is studied generally for

A
ferromagnetic materials

B
paramagnetic materials

C
diamagnetic materials

D
All of the above

Solution

In paramagnetic and diamagnetic materials induced magnetism is very feeble to study the hysterisis loop for them. In ferromagnetic materials induced magnetism is enough to study hysterisis loop.
Question 12
1 / -0

The B-H curve (i) and (ii) shown in the given figure is associated with

A
(i) diamagnetic and (ii) paramagnetic substance

B
(i) paramagnetic and (ii) ferromagnetic substance

C
(i) soft iron (ii) steel

D
(i) steel and (ii) soft iron

Solution

The loop-I is narrower than loop-II, Retentivity is more in case of steel.
Hence, loop-I is for soft iron and loop-II is for steel.
Question 13
1 / -0

The narrowest hysterisis loop is for

A
cobalt steel

B
almico

C
soft magnetic material

D
stainless steel

Solution

A narrow hysteresis loop implies a small amount of dissipated energy. This occurs as a result of its small area and therefore more frequently repeated reversals of applied magnetising force. Soft magnetic are materials used in devices that require alternating magnetic fields have these narrow hysteresis shapes.
Question 14
1 / -0

In a cassette player, material used for coating magnetic tapes is :

A
cobalt

B
$$Co{Fe}_{2}{O}_{4}$$

C
$$Ni{Fe}_{2}{O}_{4}$$

D
nickel

Solution

In cassette player, materials used for magnetic tapes is $$Ni{ Fe }_{ 2 }{ O }_{ 4 }.$$
Ferrites (Ferromagnetic material) is used for Coating magnetic tapes. In cassette player or for building memory store in modern computers. Most common ones are $$MnFe_2{0}_4, FeFe_20_4,NiFe_20_4$$ etc.
Hence, the answer is $$NiFe_20_4.$$
Question 15
1 / -0

Th direction of magnetic lines of force of a bar magnet is:

A
from south to north pole

B
from north to south pole

C
across the bar magnet

D
from south to north pole inside the magnet and from north to south pole outside the magnet

Solution

The direction of magnetic lines of force of a bar magnet is from north to south pole outside the magnet and from south pole to north pole inside the magnet as shown in figure.
Question 16
1 / -0

Curie temperature is the temperature above which

A
a ferromagnetic material becomes paramagnetic

B
a paramagnetic material becomes diamagnetic

C
a ferromagnetic material becomes diamagnetic

D
a paramagnetic material becomes ferromagnetic

Solution

Curie temperature ($$T_c$$), or Curie point, is the temperature where a material's permanent magnetism changes to induced magnetism
Question 17
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Susceptibility is positive and large for a

A
paramagnetic substance

B
ferromagntic substance

C
diamagnetic substance

D
non magnetic substance

Solution

For ferromagnetic substances, $$\chi_m$$ is large and positive.
Question 18
1 / -0

A ferromagnetic material is heated above its curie temperature. Which one of a correct statement?

A
Ferromagneitc domains are perfectly arranged

B
Ferromagnetic domains become random

C
Ferromagnetic domains are not influenced

D
Ferromagnetic material changes into diamagnetic material

Solution

Beyond curie temperature, ferromagnetic material turns into paramagnetic material, as the ferromagnetic domains become random.
Question 19
1 / -0

Hysterisis is the phenomenon of lagging of

A
$$I$$ behind $$B$$

B
$$B$$ behind $$I$$

C
$$I$$ and $$B$$ behind $$H$$

D
$$H$$ behind $$I$$

Solution

When we increase $$H$$ then $$I$$ also increases but when we decrease $$H$$
$$I$$ does not becomes zero, and so as $$B$$ if we plot $$B vs H$$ curve instead of $$I vs H$$
Therefore, $$B$$ and $$I$$ lags behind $$H$$.

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Magnetism and Matter Test -6

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Magnetism and Matter Test -6

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Question 1

strong interactions between atomic magnetic moments cause them to line up parallel to each other in regions called magnetic domains even if there is no external field

atomic magnetic moments are random in strong external fields

weak interactions between atomic magnetic moments cause them to line up anti parallel to each other in external field

strong interactions between atomic magnetic moments cause them to line up anti parallel to each other in external field

Solution

Question 2

low retentivity and high coercivity

low retentivity and low coercivity

high retentivity and low coercivity

high retentivity and high coercivity

Solution

Question 3

paramagnetic substance

soft ferromagnetic substance

diamagnetic substance

air

Solution

Question 4

18o

greater

0o

smaller

Solution

Question 5

Lines seem to come out at 45 degrees to the ground

Lines seem to come out of the ground

Lines seem to be horizontal to the ground

Lines seem to go into the ground

Solution

Question 6

Ferromagnetic material

Insulating material

Paramagnetic material

Diamagnetic material

Solution

Question 7

heat generated is very low

more heat is generated

heat generated is ultra low

no heat is generated

Solution

Question 8

south to north

east to west

west to east

north to south

Solution

Question 9

7.0 × 105 A/m

6.0 × 105 A/m

9.0 × 105A/m

8.0 × 105 A/m

Solution

Question 10

decrease with the decrease in distance from the magnet

decrease with the increase in distance from the magnet

remain constant with increase in distance from magnet

becomes zero with decrease in distance from magnet

Solution

Question 11

ferromagnetic materials

paramagnetic materials

diamagnetic materials

All of the above

Solution

Question 12

(i) diamagnetic and (ii) paramagnetic substance

(i) paramagnetic and (ii) ferromagnetic substance

(i) soft iron (ii) steel

(i) steel and (ii) soft iron

Solution

18^o

0^o

7.0 × 10⁵A/m

6.0 × 10⁵A/m

9.0 × 10⁵A/m

8.0 × 10⁵A/m