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JEE Mains · Physics · STD 12 - 4. Moving charges and magnetism

The magnetic field inside a 200 turns solenoid of radius 10 cm is \(2.9 \times 10^{-4} \mathrm{Tesla}\). If the solenoid carries a current of 0.29 A , then the length of the solenoid is ________ \(\pi \mathrm{cm}\).

  1. A 10
  2. B 8
  3. C 6
  4. D 4
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Answer & Solution

Correct Answer

(B) 8

Step-by-step Solution

Detailed explanation

Assuming long solenoid \(\begin{aligned} & \mathrm{B}=\mu_0\left(\frac{\mathrm{~N}}{\ell}\right) \mathrm{i} \\ & \ell=\frac{\mu_0 \mathrm{Ni}}{\mathrm{~B}}=\frac{\left(4 \pi \times 10^{-7}\right)(200)(0.29)}{2.9 \times 10^{-4}} \mathrm{~m} \\ & =8 \pi \mathrm{~cm} \end{aligned}\)
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