Which one of the following statements regarding a current-carrying solenoid is not correct?
- A.The magnetic field inside the solenoid is uniform.
- B.The current-carrying solenoid behaves like a bar magnet.
- C.The magnetic field inside the solenoid increases with increase in current.
- D.If a soft iron bar is inserted inside the solenoid, the magnetic field remains the same.
Correct answer
Explanation
The correct answer is D. Putting a soft iron bar inside a solenoid makes the magnetic field much stronger, so the claim that the field stays the same is not correct.
A solenoid is a long coil of insulated wire wound in the shape of a cylinder. When current flows, its field lines inside are parallel and evenly spaced, so the field there is uniform, and outside it looks like the field of a bar magnet, with a north and a south pole at the two ends. The field inside is B = μ₀nI, so it grows with the current I and the number of turns per unit length n. Soft iron has a very high permeability; it becomes magnetised and multiplies the field many times. This is how an electromagnet is made.
A is wrong as a choice: the field inside a long solenoid is indeed uniform.
B is wrong as a choice: a current-carrying solenoid does behave like a bar magnet.
C is wrong as a choice: a larger current gives a stronger field.
Exam tip: solenoid plus soft iron core equals an electromagnet; the field is B = μ₀nI.
Practice Questions
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- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
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- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
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- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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