Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R)
Assertion (A) : Magnetic monopoles do not exist.
Reason (R) : Magnetic field lines are continuous and form closed loops.
In the light of the above statements, choose the most appropriate answer from the options given below :
A
Both (A) and (R) are correct but (R) is not the correct explanation of (A)
B
(A) is correct but (R) is not correct
C
Both (A) and (R) are correct and (R) is the correct explanation of (A)
D
(A) is not correct but (R) is correct
Answer
Correct answer:C
Step-by-step solution
Standard Method
Given:
Assertion (A): Magnetic monopoles do not exist.
Reason (R): Magnetic field lines are continuous and form closed loops.
Find: Whether Assertion (A) and Reason (R) are correct, and whether Reason (R) correctly explains Assertion (A).
To analyze the given statements, examine the assertion and the reason.
Magnetic monopoles refer to hypothetical particles that have only a single magnetic pole. In contrast, all known magnets have both a north pole and a south pole. As of modern physics, magnetic monopoles have not been observed in nature. Therefore, Assertion (A) is correct.
Magnetic field lines provide a visual representation of a magnetic field. These lines are continuous and always form closed loops. They do not begin or end at any isolated magnetic charge. Therefore, Reason (R) is correct.
This is also consistent with Gauss's law for magnetism:
∮B⋅dA=0
This implies that the net magnetic flux through any closed surface is zero, so isolated magnetic poles do not exist.
Since magnetic field lines form closed loops, they support the statement that magnetic monopoles do not exist.
Therefore, both Assertion (A) and Reason (R) are correct, and Reason (R) is the correct explanation of Assertion (A). The correct option is C.
Stepwise Explanation
Given:
Assertion (A): Magnetic monopoles do not exist.
Reason (R): Magnetic field lines are continuous and form closed loops.
Find: Whether the reason correctly explains the assertion.
Step 1: Analyze Assertion (A).
Assertion (A) states that magnetic monopoles do not exist. This is a fundamental principle in magnetism, supported by experimental evidence so far. While some theoretical ideas suggest their possibility, they have not been observed. Therefore, Assertion (A) is correct.
Step 2: Analyze Reason (R).
Reason (R) states that magnetic field lines are continuous and form closed loops. This follows from Gauss's law for magnetism:
∮B⋅dA=0
This means there are no isolated magnetic poles acting as sources or sinks of magnetic field. Hence, Reason (R) is also correct.
Step 3: Check whether Reason (R) explains Assertion (A).
If magnetic monopoles existed, magnetic field lines could start from one monopole and end on another, instead of always forming closed loops. Since magnetic field lines are continuous and form closed loops, this reflects the absence of isolated magnetic poles.
Therefore, Reason (R) is the correct explanation of Assertion (A).
Thus, both statements are correct and the correct option is C.
Common mistakes
A common mistake is to think that magnetic field lines start at the north pole and end at the south pole permanently. That is incomplete because outside the magnet they go from north to south, but inside the magnet they continue back, forming closed loops. Always remember the full closed-loop picture.
Students sometimes confuse electric field lines with magnetic field lines. Electric field lines can begin or end on charges, but magnetic field lines do not because isolated magnetic monopoles are not observed. Use the correct field-line model for magnetism.
Another mistake is to treat the reason as merely a related fact rather than an explanation. Here the closed-loop nature of magnetic field lines directly reflects the absence of isolated magnetic poles, so the reason does explain the assertion.
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