ROUTERA

Magnetism and Matter

Class 12th Physics Chapter Case Study

Case Study 1: Magnetic Materials and Their Classification

Magnetic materials can be classified into different categories based on their magnetic properties: diamagnetic, paramagnetic, and ferromagnetic.

  • Diamagnetic materials have no permanent magnetic dipoles and are weakly repelled by a magnetic field (e.g., copper, bismuth).
  • Paramagnetic materials have a small, positive susceptibility to magnetic fields and are weakly attracted (e.g., aluminum, platinum).
  • Ferromagnetic materials possess permanent magnetic dipoles and are strongly attracted to magnetic fields (e.g., iron, nickel).

Questions:

  1. Which of the following materials is classified as a diamagnetic material?
    • a) Iron
    • b) Copper
    • c) Cobalt
    • d) Aluminum
  2. Paramagnetic materials have:
    • a) No magnetic dipoles
    • b) Permanent magnetic dipoles
    • c) Temporary magnetic dipoles
    • d) Strong magnetic properties
  3. Ferromagnetic materials can be magnetized by:
    • a) A weak magnetic field
    • b) High temperatures
    • c) Mechanical stress
    • d) Strong magnetic fields
  4. The magnetic susceptibility of diamagnetic materials is:
    • a) Greater than 0
    • b) Less than 0
    • c) Equal to 0
    • d) Infinite

Answers:

  1. b) Copper
  2. c) Temporary magnetic dipoles
  3. d) Strong magnetic fields
  4. b) Less than 0

Case Study 2: Magnetic Field of a Magnet

A bar magnet produces a magnetic field in the surrounding space, represented by magnetic field lines. The field lines emerge from the north pole and enter the south pole, showing the direction of the magnetic force. The strength of the magnetic field can be measured using a magnetic compass.

Questions:

  1. The magnetic field lines of a bar magnet are:
    • a) Straight lines
    • b) Circular
    • c) Closed loops
    • d) Divergent
  2. The density of magnetic field lines indicates:
    • a) Direction of the field
    • b) Strength of the field
    • c) Type of magnet
    • d) Speed of the magnet
  3. A magnetic compass points towards:
    • a) The south pole of the magnet
    • b) The north pole of the magnet
    • c) The center of the magnet
    • d) The earth's magnetic field
  4. The region around a magnet where magnetic forces can be detected is called:
    • a) Magnetic domain
    • b) Magnetic field
    • c) Magnetic dipole
    • d) Magnetic line

Answers:

  1. c) Closed loops
  2. b) Strength of the field
  3. b) The north pole of the magnet
  4. b) Magnetic field

Case Study 3: Earth’s Magnetic Field

The Earth itself behaves like a giant magnet with a magnetic field that can be represented using magnetic field lines. The geographic north pole of the Earth is actually near the magnetic south pole, which is why compasses point north. The Earth's magnetic field is essential for navigation and also protects the planet from solar wind.

Questions:

  1. The direction a compass points is determined by:
    • a) The Earth's gravitational field
    • b) The Earth's magnetic field
    • c) The Earth's electric field
    • d) The Earth's rotational motion
  2. The angle between the magnetic field and the horizontal plane is known as:
    • a) Magnetic declination
    • b) Magnetic inclination
    • c) Magnetic susceptibility
    • d) Magnetic permeability
  3. The region around the Earth where its magnetic field is effective is called:
    • a) Magnetosphere
    • b) Lithosphere
    • c) Atmosphere
    • d) Hydrosphere
  4. The magnetic field strength of the Earth is approximately:
    • a) 10 T
    • b) 0.5 T
    • c) 50 μT
    • d) 500 mT

Answers:

  1. b) The Earth's magnetic field
  2. b) Magnetic inclination
  3. a) Magnetosphere
  4. c) 50 μT

Case Study 4: Magnetization and Magnetic Hysteresis

Magnetization is the process of inducing magnetic properties in a material. When a magnetic material is subjected to an external magnetic field, it becomes magnetized. When the external field is removed, the material may retain some magnetization, leading to hysteresis.

Questions:

  1. Magnetization is defined as:
    • a) The process of creating a magnetic field
    • b) The ability to repel magnetic fields
    • c) The density of magnetic dipole moments in a material
    • d) The loss of magnetic properties
  2. The phenomenon where a material retains some magnetization after the external magnetic field is removed is known as:
    • a) Magnetic declination
    • b) Magnetic susceptibility
    • c) Magnetic hysteresis
    • d) Magnetic permeability
  3. In a hysteresis loop, the area represents:
    • a) Energy loss
    • b) Energy gain
    • c) Magnetic field strength
    • d) Magnetic flux
  4. The point at which a material becomes fully magnetized is called:
    • a) Saturation magnetization
    • b) Remanent magnetization
    • c) Coercivity
    • d) Magnetostriction

Answers:

  1. c) The density of magnetic dipole moments in a material
  2. c) Magnetic hysteresis
  3. a) Energy loss
  4. a) Saturation magnetization

Case Study 5: Applications of Magnetism

Magnetism has numerous applications in technology, such as magnetic storage devices (hard drives), electric motors, and transformers. Understanding magnetic properties is crucial for designing efficient devices.

Questions:

  1. Which of the following devices utilizes magnetism to operate?
    • a) Light bulb
    • b) Electric motor
    • c) Battery
    • d) Capacitor
  2. Hard drives store data using:
    • a) Electric fields
    • b) Magnetic fields
    • c) Optical storage
    • d) Mechanical storage
  3. In transformers, magnetism is used to:
    • a) Convert AC to DC
    • b) Increase or decrease voltage levels
    • c) Store electrical energy
    • d) Measure electric current
  4. A magnetic levitation train (maglev) operates on the principle of:
    • a) Electromagnetism
    • b) Gravity
    • c) Static electricity
    • d) Kinetic energy

Answers:

  1. b) Electric motor
  2. b) Magnetic fields
  3. b) Increase or decrease voltage levels
  4. a) Electromagnetism