A uniform current-carrying narrow solenoid produces
- A.uniform magnetic field inside the solenoid
- B.uniform magnetic field outside the solenoid
- C.magnetic field with straight field lines in all the regions
- D.magnetic field with oscillating nature
Correct answer
Explanation
The correct answer is A, uniform magnetic field inside the solenoid. Inside a long, narrow solenoid the field lines run straight and parallel and are evenly spaced, which is the picture of a uniform field.
A solenoid is a wire wound in a close helix. When a steady current flows, the fields of all the turns add up along the axis, giving a strong field B = μ₀nI, where n is the number of turns per unit length and I the current. The field does not depend on the position inside, so a soft-iron core placed there becomes an electromagnet. Outside, the field lines spread out and the field is very weak, almost zero for a long solenoid.
B is wrong because the field outside is weak and non-uniform. C is wrong because the lines curve round outside and are straight only inside. D is wrong because a steady direct current gives a steady field, not an oscillating one.
Exam tip: solenoid field inside = μ₀nI, uniform like a bar magnet's interior; outside ≈ 0.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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