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A solenoid of length 0.25 m has a radius of 1 cm and is made up of 500 turns. It carries a current of 2.5 A. What is the magnitude of the magnetic field inside the solenoid? (μ₀=4π×10⁻⁷ SI)

Asked in GUJCET 2022 · Solenoid, toroid and field energy

• (1) 6.28×10⁻³ T
• (2) 6.28×10⁻² T
• (3) 6.28×10⁻⁴ T
• (4) 6.28×10⁻¹ T

Step-by-step solution

Why the other options are wrong

• (2) Reads the length as 0.025 m, which makes n=2×10⁴ m⁻¹ and the field ten times too large.
• (3) Divides the 500 turns by the current 2.5 instead of the length 0.25 (the same slip as reading the length as 2.5 m), giving n=200 m⁻¹ — ten times too few turns per metre.
• (4) Reads the length as 0.25 cm, so n=2×10⁵ m⁻¹ and the field comes out a hundred times too large.

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