
The curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with . The current that should be passed in the solenoid to demagnetize a ferromagnet completely is:
a)
b)
c)
d) None of these

Answer
492.3k+ views
Hint: B-H curve shows that a given material doesn’t not follow the same path during magnetization and demagnetization. This creates a difference in the current, which is responsible for reduction of magnetization of the material. The current, at which the current demagnetizes, no longer remains zero but has a negative value. We will use this concept along with the basic formula to find the answer.
Formula used:
Complete step by step answer:
The B-H curve represents the magnetization and demagnetization characteristics of a ferromagnetic material. It shows the amount of current required for a particular magnetization to be achieved. It also shows that for a given ferromagnetic material, the path traced during magnetization and demagnetization are not the same.
We know that the magnetic intensity has a unique relation with the current passing through the conducting wire along with the number turns. This relation is as follows:
Where, is the magnetic field intensity, is the length of conductor, is the number of turns, is the current through the conductor.
We can modify the above equation as:
------(i)
Here, it can be clearly seen that for the complete demagnetization of the ferromagnetic material, the y-axis component must be zero, i.e., . Clearly, at this point the value of is .
Putting this value of in equation (i), we get:
So, the correct answer is “Option B”.
Note: Don’t panic when length is not mentioned in such questions. Generally, the length is already present in other parameters often disguised. For example, here length was present in the given in question as . Hence, because of this, we did not require the absolute length to solve the question.
Formula used:
Complete step by step answer:
The B-H curve represents the magnetization and demagnetization characteristics of a ferromagnetic material. It shows the amount of current required for a particular magnetization to be achieved. It also shows that for a given ferromagnetic material, the path traced during magnetization and demagnetization are not the same.
We know that the magnetic intensity has a unique relation with the current passing through the conducting wire along with the number turns. This relation is as follows:
Where,
We can modify the above equation as:
Here, it can be clearly seen that for the complete demagnetization of the ferromagnetic material, the y-axis component must be zero, i.e.,
Putting this value of
So, the correct answer is “Option B”.
Note: Don’t panic when length is not mentioned in such questions. Generally, the length is already present in other parameters often disguised. For example, here length was present in the
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