NEETPhysicsMagnetic Properties of Matter
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): If the uniform magnetic field in which a magnetic needle oscillates is increased by 300 % , its time period becomes half of its initial value. Reason (R): The time period of oscillation of a magnetic dipole is inversely proportional to the square root of the magnitude of the magnetic field. In the
Options
- ABoth (A) and (R) are true but (R) is not the correct explanation of (A).
- BBoth (A) and (R) are true and (R) is the correct explanation of (A).
- C(A) is true but (R) is false.
- D(A) is false but (R) is true.
Correct answer
B. Both (A) and (R) are true and (R) is the correct explanation of (A).
Step-by-step solution
The time period of oscillation of a magnetic dipole in a uniform magnetic field is given by T = 2 I MB . From this formula, it is clear that T 1 B . Hence, the Reason (R) is true. If the magnetic field is increased by 300 % , the new magnetic field becomes: B' = B + 300 100 B = 4B The new time period T' will be: T' 1 B' = 1 4B = 1 2 B Therefore, T' = T 2 . The time period becomes half of its initial value. Hence, the Assertion (A) is true. Since the inverse square root relationship directly leads to the halving of