Saved Bookmarks
| 1. |
Many of the diagrams given in figure show magnetic field lines (thick lines in the figure ) wrongly. Point out what is wrong with them . Some of them may describe electrostatic field lines correctly. Point out which ones. |
|
Answer» Solution :a. Wrong Magnetic field lines can never emanate from , as shown in figure . Over any closed surface , the net flux of B must always be ZERO., i.e. ., pictorially as many field lines should seem to enter the surface as the number of lines leaving it . The field lines shown , in fact , represent ELECTRIC field of a long positively charged wire. The correct magnetic field lines are circling the straight conductor. b. Wrong Magnetic field lines (like electric field lines ) can never cross each other, because otherwise the direction of field at the point of intersection in ambiguous . There is further error in the figure Magnetostatic field lines can never form closed loops around empty space. A closed loop of static magnetic field line must enclose a region across which a current is passing . By contrast , electrostatic field lines can never form closed loops, neither in empty space, nor when the loop ENCLOSES charges . c. Right Magnetic lines ae completely confined within a toroid Noting wrong in field lines forming closed loops, since each encloses across which a current passes . For clarity of figure , only a few field lines within the toroid have been shown . Actually, the entire region enclosed by the windings contains magnetic field. d. WrongField lines due to a solenoid at its ends and outside cannot be so completely straight and confined , such a thing violates Ampere.s law. The lines should CURVE out at both ends, and meet eventually to form closed loops. e. Right There are field lines out side and inside a bar MAGNET .Note carefully the direction of field lines inside . Not all field lines emanate out of a north pole (or converge into a south pole) . Around both the N-pole , and the net flux of the field is zero. f. Wrong These field lines cannot possibly represent a magnetic field . Look at the upper region All the field lines seem to emanate out of the shaded plate . The net flux through a surface surrounding the shaded plate is not zero. This is impossible for a magnetic field . The given field lines , in fact, show the electrostatic field lines around a positively charged upper plate and a negatively charged lower plate. g. Wrong Magnetic field lines between two pole pieces be precisely straight at the ends. Some fringing of lines is inevitable . Otherwise, Ampere .s law is violated. This is also true for electric field lines. |
|