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JEE Advanced2025PhysicsElectromagnetic InductionActual

A conducting square loop of side L , mass M and resistance R is moving in the X Y plane with its edges parallel to the X and Y axes. The region y 0 has a uniform magnetic field, B =B₀ k . The magnetic field is zero everywhere else. At time t=0 , the loop starts to enter the magnetic field with an initial velocity v₀ ~m / s , as shown in the figure. Considering the quantity K= B₀^2 L^2 R M in appropriate units, ignori

Options

  1. AIf v₀=1.5 K L , the loop will stop before it enters completely inside the region of magnetic field.
  2. BWhen the complete loop is inside the region of magnetic field, the net force acting on the loop is zero.
  3. CIf v₀= K L 10 , the loop comes to rest at t= ( 1 K ) ( 5 2 ) .
  4. DIf v₀=3 K L , the complete loop enters inside the region of magnetic field at time t= ( 1 K ) ( 3 2 ) .

Correct answer

B. When the complete loop is inside the region of magnetic field, the net force acting on the loop is zero.

Step-by-step solution

- d dt = d dt ( B ₀ y )= BV aligned & F = B ( i )( )(- j ) & ma =- B ₀ [ ~B ₀ ~V R ]( ) & a =- B ₀^2 ^2 ~V mR aligned aligned & Also K= B₀^2 ^2 V R M & So [a=-k v] & d v d t =-k v & _ v₀ ^v d v d t = ₀^t-k d t & n v v₀ =-k t aligned [ v = v ₀ e ^ - kt ] [ v = v ₀ e ^ - kt ] .( i ) dx dt = v ₀ e ^ - kt ( x ) aligned & ₀^ x dx = ₀^ t v ₀ e ^ - kt dt & = v ₀ k (1- e ^ - kt ) aligned When x= = V ₀ k (1- e ^ - kt ) Option (D) ( v ₀=3 k ) aligned & = 3 k k (1- e ^ - kt ) & 1 3 =1- e ^ - kt & f 2 3 =2 e ^ - kt & - kt =8 n

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