This set of Engineering Materials and Metallurgy online test focuses on “Ferro, Para and Dia Magnetic Materials”.
1. How is the magnetic induction of a material defined?
a) Wb m-2
b) A m2
c) A m-2
d) H m-1
Explanation: Electromagnetic induction is the production of a voltage in an electrical conductor having a varying magnetic field. It is defined as Weber per square meter or Tesla (T). Saturation induction Ba and residual induction BT are also given by the same unit.
2. The measure of capacity of a material to produce its own magnetic field is defined as _______
a) Magnetic induction
d) Magnetic moment
Explanation: Permeability in electromagnetism is defined as its ability of formation of a magnetic field in itself. Magnetic permeability is given as Henry per meter (H m-1) and is denoted by the symbol .
3. How is the magnetic field strength defined?
a) Wb m-2
b) A m2
c) A m-2
d) H m-1
Explanation: The strength of a magnetic field produced as a result of moving charges and dipoles is known as magnetic field strength (H). Mathematically, it is denoted by with its SI units given in ampere per meter (A m-1).
4. What is the permeability of free space?
a) 4 * 10-6
b) 4 * 10-7
c) 4 * 10-8
d) 4 * 10-9
Explanation: Permeability is defined as the ability of a material to form a magnetic field within itself. The permeability of free space is denoted by and has a constant value of 4 * 10-7 H m-1.
5. How is magnetic moment determined?
a) Planck unit
b) Bohr magneton
c) Eddington number
d) Sommerfield number
Explanation: The magnetic moment is the amount of torque produced in a magnetic field. This is expressed in terms of the constant known as Bohr magneton.
Explanation: Bohr magneton is defined as that constant which is used to express the magnetic moment of an electron. It is mathematically defined by . It has a constant value of 9.273 * 10-24 A m2 in case of SI units and 9.273 * 10-21 A m2 in case of CGS units.
7. The measure of a material which helps to determine whether it is attracted to or repelled from a magnetic field is known as _______
Explanation: In electromagnetism, susceptibility is defined as a measure which is used to identify whether a material is attracted to or repelled on the application of a magnetic field. It is denoted by X and is mathematically defined as.
8. _______ is a weak magnetizing effect in which magnetic lines of force are repelled.
Explanation: Diamagnetism is caused due to the modifications of motion of electrons which produces an opposing magnetic field. The magnetic lines of force are repelled, which results in weak force and low susceptibility. Copper, mercury, and gold are common examples of diamagnetic materials.
9. Which material is considered as perfectly diamagnetic?
Explanation: Superconductors are considered as perfect diamagnets due to their ability to eject magnetic force in all directions. This principle is based on the well known Meissner effect. Superconductors have a susceptibility of -1 * 105.
10. _______ is a weak magnetizing effect in which the material is attracted due to the application of magnetic force.
Explanation: The phenomenon by which the magnetic moments of atoms of a material get aligned in the direction of the magnetic field is known as paramagnetism. This force is usually small, thereby producing a weak effect.
11. What is the temperature at which a phase transition from ferromagnetic to paramagnetic occurs?
Explanation: Curie temperature is defined as that temperature at which materials lose their permanent magnetic properties. In other words, a transition from ferromagnetic state to paramagnetic phase occurs. This is otherwise also known as Curie point, named after Pierre Curie.
12. What is the temperature at which a change from anti-ferromagnetic phase to paramagnetic phase occurs?
Explanation: Neel temperature is defined as that temperature at which materials lose their magnetic ordering due to a large thermal energy. In other words, a transition from anti-ferromagnetic state to paramagnetic phase occurs. This is otherwise also known as magnetic ordering temperature and is named after Louis Neel.
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