Which of the following is a ferromagnetic material?
Analysis & Theory
Nickel exhibits strong ferromagnetism with domains that align under an external magnetic field.
What is the Curie temperature?
A
Temperature above which a ferromagnet becomes paramagnetic
B
Temperature at which magnetic saturation occurs
C
Temperature below which diamagnetism appears
D
Temperature at which coercivity is zero
Analysis & Theory
The Curie temperature is the critical point where ferromagnetic ordering is lost and the material becomes paramagnetic.
Which type of magnetic material is weakly repelled by both poles of a magnet?
Analysis & Theory
Diamagnetic materials develop an induced magnetic field opposite to the applied field and are weakly repelled.
What does the hysteresis loop of a ferromagnetic core represent?
A
The relationship between current and voltage
B
The energy lost per cycle of magnetization
C
The thermal stability of the material
D
The electric field strength
Analysis & Theory
The area inside the B–H hysteresis loop represents energy loss (hysteresis loss) per magnetization cycle.
Which of these is NOT a characteristic of a soft magnetic material?
D
Easy magnetization and demagnetization
Analysis & Theory
Soft magnetic materials have low hysteresis loss; high hysteresis loss is a trait of hard magnetic materials.
What is magnetic permeability (μ)?
A
Resistance to magnetic field penetration
B
Ratio of magnetic flux density to magnetic field strength
C
Energy stored in a magnetic field
D
Rate of change of magnetic flux
Analysis & Theory
Permeability μ = B/H, indicating how easily a material supports the formation of a magnetic field.
Which material would you choose for a permanent magnet?
Analysis & Theory
Ferrites (hard ferrites) have high coercivity and retain significant magnetization, making them suitable for permanent magnets.
What happens at magnetic saturation in a ferromagnetic core?
A
Permeability becomes infinite
B
Further increases in H produce little increase in B
C
Material becomes diamagnetic
D
Coercivity drops to zero
Analysis & Theory
At saturation, most magnetic domains are aligned, so increases in H yield minimal increases in B.
Which phenomenon describes the reversal of magnetization in a ferromagnet when the applied field is reduced to zero?
Analysis & Theory
Coercivity is the field strength needed to reduce the residual magnetization (remanence) to zero.
Paramagnetic materials are characterized by:
A
Strong permanent magnetization
B
Negative susceptibility
C
Small positive susceptibility
Analysis & Theory
Paramagnets have unpaired electrons that align with an external field, giving a small positive magnetic susceptibility.