Correct Option
The correct option is (a) 1, 2 and 3 only.
Explanation
A permanent magnet possesses magnetic properties due to the orderly alignment of its magnetic domains (microscopic regions where atomic magnetic moments are aligned in the same direction). Any external influence that provides enough energy to randomize or disrupt this alignment results in the loss of magnetism, a process known as demagnetization.
Statement-wise Analysis
- Statement 1 is Correct: Heating increases the kinetic energy of the atoms within the magnet. This thermal agitation vibrates the atoms and disrupts the alignment of the magnetic domains. If a magnet is heated above a specific temperature called the Curie temperature, it loses its ferromagnetic properties entirely and becomes paramagnetic.
- Statement 2 is Correct: Hammering delivers a sharp mechanical shock to the material. This physical impact forces the magnetic domains out of their aligned positions, causing them to become randomized, which weakens or destroys the magnetism.
- Statement 3 is Correct: Dropping from a height creates a sudden impact upon landing. Similar to hammering, this mechanical shock disturbs the orderly arrangement of the magnetic domains, leading to a loss of magnetic strength.
- Statement 4 is Incorrect: Storing in a wooden box does not cause demagnetization. Wood is a non-magnetic material and does not interact with the magnetic field in a way that disrupts domain alignment. In fact, magnets are often stored in non-magnetic containers (with soft iron keepers) to protect them.
Key Takeaway
Demagnetization occurs when the uniform alignment of magnetic domains is destroyed by external energy, primarily through thermal agitation (heating) or mechanical shock (hammering or dropping).