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NEET 2026
Exam
NEET
Year
2026
Subject
Physics
Chapter
Chapter

NEET 2026 · Physics · Chapter

A long tightly wound solenoid is used in a laboratory to generate a...

A long tightly wound solenoid is used in a laboratory to generate a uniform magnetic field of 25.12 mT25.12\text{ mT} at its center. If the solenoid has 500 turns500\text{ turns} per 10 cm10\text{ cm} of its length, what is the magnitude of the steady current flowing through it? (Take π=3.14\pi = 3.14)

Options

  1. A8 A8\text{ A}
  2. B40 A40\text{ A}
  3. C4 A4\text{ A}
  4. D400 A400\text{ A}

Correct answer

C. 4 A4\text{ A}

Step-by-step solution

The magnetic field at the center of a long tightly wound solenoid is given by the formula:

B=μ0nIB = \mu_0 n I

where nn is the number of turns per unit length and II is the current.

Given:
B=25.12 mT=25.12×10−3 TB = 25.12 \text{ mT} = 25.12 \times 10^{-3} \text{ T}
n=50010 cm=50010×10−2 m=5000 turns/mn = \dfrac{500}{10 \text{ cm}} = \dfrac{500}{10 \times 10^{-2} \text{ m}} = 5000 \text{ turns/m}
μ0=4π×10−7 T⋅m/A\mu_0 = 4\pi \times 10^{-7} \text{ T}\cdot\text{m/A}

Substituting the values into the formula:

25.12×10−3=(4×3.14×10−7)×5000×I25.12 \times 10^{-3} = (4 \times 3.14 \times 10^{-7}) \times 5000 \times I

25.12×10−3=12.56×10−7×5000×I25.12 \times 10^{-3} = 12.56 \times 10^{-7} \times 5000 \times I

25.12×10−3=6.28×10−3×I25.12 \times 10^{-3} = 6.28 \times 10^{-3} \times I

I=25.12×10−36.28×10−3I = \dfrac{25.12 \times 10^{-3}}{6.28 \times 10^{-3}}

I=4 AI = 4 \text{ A}

Answer: 4 A4\text{ A}
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