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Class 12  »  Physics  »  Magnetism and Matter

Hysteresis Loop - UNSOLVED PRACTICE SET

Class 12

Chapter: Magnetism and Matter | Topic: Hysteresis Loop

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Class 12

HYSTERESIS LOOP - UNSOLVED PRACTICE SET

Topic: Hysteresis Loop

Time: 40 mins | Marks: 30 | Difficulty: Medium

Multiple Choice Questions

Q1. The hysteresis loop of a material is a graph between:

  1. Magnetic field intensity (H) and magnetic flux density (B)
  2. Current and voltage
  3. Temperature and magnetization
  4. Time and magnetic field

Q2. The area of the hysteresis loop represents:

  1. Magnetic energy stored
  2. Energy dissipated as heat per unit volume per cycle
  3. Electrical resistance of the material
  4. Magnetic permeability

Q3. For making transformer cores, we prefer materials with:

  1. Large hysteresis loop area
  2. Small hysteresis loop area
  3. Square hysteresis loop
  4. No hysteresis loop

Q4. Retentivity of a magnetic material is:

  1. The magnetic field required to reduce magnetization to zero
  2. The residual magnetization when the magnetizing field is reduced to zero
  3. The maximum magnetization the material can achieve
  4. The temperature at which the material loses ferromagnetism

Q5. Coercivity is the measure of:

  1. How easily a material can be magnetized
  2. How easily a material can be demagnetized
  3. The maximum magnetic field the material can withstand
  4. The electrical conductivity of the material

Q6. A material with a square hysteresis loop is suitable for making:

  1. Transformer cores
  2. Permanent magnets
  3. Magnetic memory devices
  4. Electromagnets

Short Answer Questions

Q7. Define retentivity and coercivity. Which of these is desirable to be high for a permanent magnet?

Q8. Why do we prefer soft iron over steel for making electromagnet cores? Explain using the concept of hysteresis.

Q9. Sketch a typical hysteresis loop for a ferromagnetic material and label the following:

(a) Saturation point

(b) Retentivity

(c) Coercivity

Q10. What happens to the hysteresis loop area if the frequency of the alternating magnetizing field is increased? Explain.

Q11. Why does a ferromagnetic material heat up when subjected to repeated cycles of magnetization and demagnetization

Q12. Distinguish between soft magnetic materials and hard magnetic materials on the basis of their hysteresis loops.

Long Answer Questions

Q13. With the help of a neat diagram, explain how a hysteresis loop is obtained for a ferromagnetic material. Explain the significance of the loop area.

Q14. Explain why the B-H curve does not retrace its path when the magnetizing field is reversed. What does this tell us about the nature of ferromagnetic materials?

Q15. Compare the hysteresis loops of:

(i) Soft iron

(ii) Steel

(iii) Ferrite

Explain which material would be suitable for:

(a) Transformer cores

(b) Permanent magnets

(c) Magnetic recording media

Numerical & Application-Based Problems

Q16. The area of a hysteresis loop for a certain ferromagnetic material is 200 J/m³. The material is used in a transformer core that operates at 50 Hz.

(a) Calculate the energy loss per second in a core of volume 5 × 10⁻⁴ m³.

(b) If the transformer operates for 8 hours a day, calculate the total energy loss per day due to hysteresis.

(c) Suggest one way to reduce this energy loss.

Q17. A ferromagnetic material has the following properties:

Retentivity = 1.2 T

Coercivity = 50 A/m

Saturation magnetization = 1.8 T

The material is subjected to an alternating magnetic field that varies between +100 A/m and -100 A/m.

(a) Sketch the expected hysteresis loop, marking the given values.

(b) Calculate the ratio of retentivity to saturation magnetization.

(c) Would this material be more suitable for a permanent magnet or a transformer core? Justify your answer.

Q18. In your school's physics lab, you are given two iron rods — one made of soft iron and one made of steel. Your teacher asks you to determine which one would be better for making:

(a) The core of a school bell electromagnet

(b) A magnetic needle for a compass

You perform an experiment by magnetizing each rod with the same solenoid and then measuring how much magnetization remains after removing the current.

(i) Which rod retains more magnetization? What property does this demonstrate?

(ii) Draw rough sketches of the expected hysteresis loops for both materials.

(iii) Based on your observations, recommend which rod to use for each application and explain why.


Total: 30 Marks | Time: 40 mins

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