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A long solenoid has 200 turns per cm and carries a current i. The magnetic field at its centre is 6.28×10⁻² weber/m². Another long solenoid has 100 turns per cm and it carries a current i/3. The value of the magnetic field at its centre is

Asked in JEE Main 2006 · Solenoid, toroid and field energy

• (1) 1.05×10⁻⁴ Wb/m²
• (2) 1.05×10⁻² Wb/m²
• (3) 1.05×10⁻⁵ Wb/m²
• (4) 1.05×10⁻³ Wb/m²

Step-by-step solution

Why the other options are wrong

• (1) Power-of-ten slip, e.g. converting turns per cm to per m in only one solenoid.
• (3) Power-of-ten slip while taking the ratio.
• (4) Power-of-ten slip while taking the ratio.

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