All magnetic fields originate in a) Iron atoms. c) Stationary electric charges. 2. A moving electric charge produces a) Only an electric field. c) Both an electric and magnetic field. 3. A magnet does not exerts a force on a) An unmagnetized iron bar. c) A stationary electric charge. 4. A drawing of the field lines of a magnetic field provides information on a) The direction of the field only. c) Both the direction and the strength of the field. 5. The magnetic field shown below is produced by a) Two north poles. c) A north pole and a south pole. b) Permanent magnets. d) Moving electric charges. b) Only a magnetic field. d) Any of these, depending on its speed. b) A magnetized iron bar. d) A moving electric charge. b) The strength of the field only. d) The source of the field. b) Two south poles. d) A south pole and an unmagnetized iron bar.
The Correct Answer and Explanation is:
Answers:
- d) Moving electric charges
- c) Both an electric and magnetic field
- c) A stationary electric charge
- c) Both the direction and the strength of the field
- c) A north pole and a south pole
Explanation:
1. Origin of Magnetic Fields:
Magnetic fields do not originate specifically from iron atoms or stationary charges. Rather, they arise from moving electric charges (option d), which can be in the form of currents in wires, electrons orbiting atomic nuclei, or even spinning particles. In permanent magnets (like iron), the electrons’ spin and orbital motion align, creating a strong magnetic field, but the fundamental source is still the motion of charge.
2. Moving Electric Charges:
A moving electric charge produces both an electric field and a magnetic field (option c). The electric field comes from the charge itself, while the magnetic field is due to its motion. This relationship is central to electromagnetism and is described by Maxwell’s equations.
3. Magnet and Force:
A magnet does not exert a force on a stationary electric charge (option c). Magnetic forces only act on moving charges (via the Lorentz force), magnetic materials, or other magnets. An unmagnetized iron bar can still experience a force due to induced magnetization.
4. Magnetic Field Lines:
Field line drawings show both the direction and the strength (option c) of a magnetic field. The lines point from north to south and the density of the lines indicates the field’s strength: denser lines mean a stronger field.
5. Magnetic Field Source:
A typical dipole magnetic field pattern is produced by a north pole and a south pole (option c). Field lines always emerge from the north and enter the south pole, creating a closed loop that defines the magnetic field.
Understanding these principles is essential in physics, engineering, and technologies like electric motors, MRI machines, and particle accelerators.
