Question

Two bar magnets having same geometry with magnetic moments m and 2m, are firstly placed such that their similar poles are on the same side. The time period of oscillation is $T₁$. When the polarity of one is reversed, the time period is $T₂$. Then:

• A. $T₁ < T₂$
• B. $T₁ = T₂$
• C. $T₁ > T₂$
• D. $T₂ = ∞$

Hint:

Time period is inversely proportional to square root of magnetic moment.

Answer 1

The Correct Option is A

Step 1: $T = 2π \sqrtI/MB$, where M is net magnetic moment.

Step 2: Similar poles same side: $M₁ = m + 2m = 3m$. Opposite poles: $M₂ = 2m - m = m$.

Step 3: $T \propto 1/\sqrtM$, so $T₁/T₂ = \sqrtm/3m = 1/\sqrt3 < 1$, so $T₁ < T₂$.