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A long solenoid has a winding density of 200 turns per cm and carries a current i. The magnetic field at its centre is 6.28 × 10⁻² Weber/m². A second long solenoid has 100 turns per cm and carries a current i/3. What magnetic field is produced at its centre?

1. 1.05 × 10⁻² Weber/m²
2. 1.05 × 10⁻⁵ Weber/m²
3. 1.05 × 10⁻³ Weber/m²
4. 1.05 × 10⁻⁴ Weber/m²

Correct answer: 1.05 × 10⁻² Weber/m²

Solution

B = mu0*n*i, so B2 = B1*(n2/n1)*(i2/i1) = 6.28e-2*(100/200)*(1/3) = 1.05e-2 Wb/m^2.

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