Magnetism — Set 5
Physics · चुंबकत्व · Questions 41–50 of 50
Relative permeability (μr) is defined as?
Correct Answer: B. μ/μ0
Relative permeability is the ratio of a material’s permeability to vacuum permeability. It shows how much better the material supports magnetic fields than free space. For vacuum, μr equals 1.
Magnetic susceptibility (χ) in simple SI form is commonly defined as?
Correct Answer: B. χ = M/H
Susceptibility compares how much magnetization is produced for a given field strength. In simple SI form, it is written as M divided by H. It is dimensionless and can be positive or negative depending on the material.
In vacuum, the relation between magnetic flux density B and field strength H is?
Correct Answer: A. B = μ0 H
In vacuum, magnetic flux density equals μ0 times the magnetic field strength. This is a standard basic relation in SI magnetism. In materials, B can also depend on the material’s response.
The value of vacuum permeability μ0 is commonly written as?
Correct Answer: C. 4π × 10^-7 T·m/A
Vacuum permeability μ0 is commonly given as 4π × 10^-7 in SI units. It connects B and H in free space. This constant appears in many magnetic field formulas.
For a long air-core solenoid, the magnetic field inside is commonly approximated as?
Correct Answer: C. B = μ0 n I
A long solenoid produces an almost uniform field inside given by μ0 n I. Here n is turns per unit length and I is current. Increasing turns or current increases the field strength.
Which change will generally increase the strength of an electromagnet most directly?
Correct Answer: D. Increase the current through the coil
A stronger current produces a stronger magnetic field in the coil. This increases the magnetizing effect on the core as well. More turns and a soft iron core also generally increase strength.
Retentivity of a magnetic material refers to its ability to?
Correct Answer: A. Retain magnetization after the field is removed
Retentivity is the ability to keep magnetization when the magnetizing field is removed. Materials with high retentivity are good for permanent magnets. Soft iron has low retentivity, so it demagnetizes easily.
Coercivity of a magnetic material refers to the magnitude of reverse field needed to?
Correct Answer: A. Reduce magnetization to zero
Coercivity measures how hard it is to demagnetize a material. It is the reverse magnetic field needed to bring magnetization to zero. Hard magnetic materials generally have high coercivity.
The area of a hysteresis loop represents?
Correct Answer: B. Energy loss per cycle per unit volume
The loop area gives the energy lost as heat in one complete magnetization cycle. A larger area means greater hysteresis loss. Reducing this loss is important in many magnetic cores.
For many paramagnetic materials, Curie law states that magnetic susceptibility is proportional to?
Correct Answer: B. 1/absolute temperature
Curie law states that susceptibility varies inversely with absolute temperature. As temperature rises, thermal agitation reduces alignment and susceptibility falls. This simple trend is a common textbook result for many paramagnets.