Sample 1Medium
Which one of the following statements about magnetic materials is correct?
- A
The susceptibility of a paramagnetic substance increases as its temperature rises.
- B
A ferromagnetic substance remains ferromagnetic at every temperature.
- C
A diamagnetic substance has a small negative susceptibility and tends to move from a stronger to a weaker part of a non-uniform magnetic field.
- D
A superconductor placed in a magnetic field is strongly paramagnetic.
Show the answer
The answer is C.Diamagnetic materials have χ slightly negative and are pushed from stronger to weaker field. Paramagnetic χ follows Curie's law (∝ 1/T), and ferromagnetism disappears above the Curie temperature.
- A.
By Curie's law paramagnetic susceptibility varies as 1/T, so it falls as temperature rises.
- B.
Above its Curie temperature a ferromagnet becomes paramagnetic.
- D.
A superconductor expels the field (Meissner effect) and is a perfect diamagnet.
NCERT: Class 12 Physics, Chapter 5, Magnetic properties of materials
Sample 2NEET level
Consider the following statements about magnetic materials. 1. Diamagnetic substances have a small negative magnetic susceptibility. 2. The susceptibility of a paramagnetic substance increases as its temperature increases. 3. A ferromagnetic substance becomes paramagnetic above its Curie temperature. 4. A diamagnetic substance placed in a non-uniform magnetic field moves from the weaker to the stronger part of the field. Which of the above statements are correct?
- A
1 and 2 only
- B
1 and 3 only
- C
2, 3 and 4 only
- D
1, 3 and 4 only
Show the answer
The answer is B.Diamagnets have small negative χ and move from stronger to weaker field, so 4 is false; above the Curie temperature a ferromagnet becomes paramagnetic. By Curie's law the paramagnetic susceptibility is inversely proportional to absolute temperature, so 2 is false.
- A.
Statement 2 is false: by Curie's law χ ∝ 1/T, so it decreases as temperature rises.
- C.
Statements 2 and 4 are false, and statement 1 is true.
- D.
Statement 4 is false: diamagnets are repelled towards the weaker field region.
NCERT: Class 12 Physics, Chapter 5 (Magnetism and Matter), Magnetic properties of materials