Engineering Materials and Metallurgy Questions and Answers – Soft and Hard Magnetic Materials

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This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Soft and Hard Magnetic Materials”.

1. The hysteresis loss in soft magnetic materials must be kept ______
a) High
b) Minimum
c) Zero
d) Unaltered
View Answer

Answer: b
Explanation: Soft magnetic materials are used in cases where regular reversal of magnetization path is required. The hysteresis losses in such materials must be kept to a minimum. This is due to a smaller hysteresis area.

2. The supermaloy primarily composed of ________________
a) Nickel
b) Iron
c) Cobalt
d) Copper
View Answer

Answer: a
Explanation: Permalloy is a magnetic material invented by the scientist Gustav Elmen. It is composed of just about 80% nickel and 5% molybdenum. It has a high relative permeability of 105.

3. Which of the following is an example of soft magnetic material?
a) Permalloy
b) Strontium
c) Alnico
d) Neodymium
View Answer

Answer: a
Explanation: Permalloy is a soft magnet mainly used in electrical and electronic applications. It is composed of roughly 45% nickel. It has a high relative permeability of around 2700.
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4. What is the relative permeability of iron?
a) 250
b) 1500
c) 2700
d) 100,000
View Answer

Answer: a
Explanation: Relative permeability is the measure of the effective permeability of a material. Commercial iron has a relative permeability of 250. The values of relative permeability of Fe-Si, permalloy, and supermaloy are 1500, 2700, and 100000 in that order.

5. The heat treatment of alnico alloys at _____ results in phase separation.
a) 100oC
b) 200oC
c) 400oC
d) 800oC
View Answer

Answer: d
Explanation: Some materials are heat treated in a magnetic field to enhance their properties. At just about 800oC, alnico undergoes a phase separation into two phases having different compositions and amount of magnetizations.

6. What is the hysteresis loss of permalloy?
a) 500
b) 120
c) 40
d) 21
View Answer

Answer: b
Explanation: Hysteresis loss of soft magnetic materials is generally kept low due to the small area. This value resides at 120 J m-3 for permalloy and even lower at 21 J m-3 for supermaloy.

7. Which of the following is a property of a hard magnetic material?
a) Low hysteresis
b) Low eddy loss
c) Low coercive force
d) High residual induction
View Answer

Answer: d
Explanation: Hard magnetic materials are used to produce permanent magnets. These permanent magnets have a high residual induction and large coercive force. Low hysteresis and Low eddy loss are properties of soft magnetic materials.
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8. A _____ cooling rate solidifies metallic glass made from iron- base alloys.
a) 10oC s-1
b) 100oC s-1
c) 1000oC s-1
d) 10000oC s-1
View Answer

Answer: d
Explanation: Metallic glasses produced from iron-base alloys are used to provide a reduction in core losses. When such an alloy is cooled at 104oC s-1, it solidifies into a ribbon-shaped metallic glass instead of crystallization.

9. Which of the following is not a use of magnesium-manganese ferrites?
a) Microwave isolator
b) Gyrators
c) Wires
d) Memory core of computer
View Answer

Answer: c
Explanation: Magnesium-manganese ferrites having high resistivity are used as microwave insulators and gyrators in the KHz and MHz range. They are also used in memory cores of the computer when there is higher manganese to magnesium ratio.
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10. Yttrium-iron-garnet is used as microwave isolators in the ____ range.
a) KHz
b) MHz
c) GHz
d) THz
View Answer

Answer: c
Explanation: Garnets such as Y3Fe5O12 (yttrium-iron-garnet)have a narrow resonance line width. These are popularly used as microwave isolators in the GHz range.

11. What is the coercive force of high carbon steel?
a) 3.98
b) 5.57
c) 18.31
d) 60
View Answer

Answer: a
Explanation: Coercive force is defined as the ability of a material to withstand a magnetic field. It is denoted by Hc and must be larger for permanent magnets (hard magnetic material). High carbon steel has a coercive force of 3.98 kA m-1.

12. What is the value of residual induction of alnico alloys?
a) 0.9
b) 0.95
c) 1.0
d) 0.8-1.2
View Answer

Answer: c
Explanation: Alnico is a common hard magnetic material containing aluminum, nickel, and cobalt (Al-Ni-Co). It has a residual induction (Br) of 0.8 to 1.2 Wb m-2 and a coercive force (Hc) of 60-12 kA m-1.

Sanfoundry Global Education & Learning Series – Engineering Materials & Metallurgy.

To practice all areas of Engineering Materials & Metallurgy, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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