Microwave Engineering Multiple Choice Questions on “Properties of Ferrimagnetic Materials”.
1. Example of a non reciprocal device:
A. Branch line coupler
B. Wilkinson coupler
C. Magic-T hybrid
D. Circulator
Answer: D
Clarification: Non reciprocal device is the one in which the response between any two ports I and j of a component depends on the direction of signal flow. Circulator is a device that allows power flow either in clockwise direction or counter clockwise direction.
2. A microwave network can be called non reciprocal only if it contains anisotropic materials like ferrite materials.
A. True
B. False
Answer: B
Clarification: A microwave network consisting of active non linear devices like transistor amplifiers, ferrite phase shifters and more. Presence of active devices or anisotropic materials can make a microwave network non reciprocal.
3. This is not an example of anisotropic material:
A. Yttrium aluminum garnet
B. Aluminum
C. Cobalt
D. Silicon
Answer: D
Clarification: Yttrium aluminum garnet is a ferromagnetic compound. Aluminum and cobalt are iron oxides that are anisotropic. Silicon is a non metal that is isotropic in nature.
4. The magnetic properties of a material are due to the existence of ___________
A. Electrons in atoms
B. Electric dipole moment
C. Magnetic dipole moment
D. None of the mentioned
Answer: C
Clarification: The magnetic properties of ferromagnetic materials are due to the existence of magnetic dipole moments, which arise primarily from electron spin. The magnetic dipole moment of an electron is 9.27×10-24 A-m2.
5. ___________ is a measure of the relative contributions of the orbital moment and the spin moment to the total magnetic moment.
A. Lande’s factor
B. Gibbs factor
C. Newton’s ratio
D. None of the mentioned
Answer: A
Clarification: An electron in orbit around a nucleus gives rise to an effective current loop and thus an additional magnetic moment, but this effect is negligible compared to the magnetic moment due to spin. Lande’s factor is a relative measure of these orbital moments.
6. Lande’s factor for all ferromagnetic materials is in the range of 0 to 1.
A. True
B. False
Answer: B
Clarification: Lande’s factor (g) is one when the moment is only due to orbital motion and 2 when the moment is only due to spin. For most microwave ferrite materials, g lies between 1.98 and 2.01.
7. The variation of magnetic moment of a ferromagnetic material with applied bias field is linear.
A. True
B. False
Answer: B
Clarification: With the increase in the applied bias field to a ferromagnetic material, the magnetic moment increases exponentially initially, after a certain applied bias field magnetic moment remains a constant.
8. A permanent magnet is made by placing the magnetic material in a strong magnetic field.
A. True
B. False
Answer: A
Clarification: A permanent magnet is made by placing the magnetic material in a strong magnetic field and then removing the field to leave the material magnetized in a remanent state.
9. The operating point of a permanent magnet is in the:
A. First quadrant
B. Second quadrant
C. Third quadrant
D. Fourth quadrant
Answer: B
Clarification: Unless the magnet shape forms a closed path, the demagnetization factors at the magnet ends will cause a slightly negative H field to be induced in the magnet. Thus the “operating point “of a permanent magnet will be in the second quadrant. This portion of the curve is called demagnetization curve.
10. After demagnetization of a magnetic material, the residual magnetization retained in the magnetic material is called:
A. Remanence
B. Residue
C. Retardation
D. None of the mentioned
Answer: A
Clarification: The residual magnetization called remanence characterizes the strength of the magnet, so magnetic material with large remanence is chosen.
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