Example 5.3: spot the wrong field linesउदाहरण 5.3: गलत क्षेत्र रेखाएँ पहचानेंExample 5.3: spot the wrong field lines
NCERT Fig 5.6 · Class 12 Physics · Chapter 5 · interactive diagram
Parts and what they mean
- (a) Wrong ((a) गलत) — Magnetic lines can never start from a point or a line: the flux through a closed surface round the wire would not be zero. This is the ELECTRIC field of a long positively charged wire. The real B of a current-carrying wire circles the wire.
- (b) Wrong ((b) गलत) — Field lines can never cross (the direction at the crossing would not be unique). Also, a closed loop of static B must enclose a current — here the loops enclose empty space.
- (c) Right — toroid ((c) सही — टोरॉइड) — Lines are closed loops confined inside the toroid; each loop encloses the current in the windings. (Only a few lines are drawn; the whole region inside the windings has field.)
- (d) Wrong ((d) गलत) — Lines of a solenoid cannot stay perfectly straight and confined beyond its ends — that violates Ampere’s law. They must curve out at both ends and close on themselves.
- (e) Right — bar magnet ((e) सही — छड़ चुंबक) — Lines outside and inside a bar magnet form closed loops (inside, from S to N). Around each pole the net flux is zero.
- (f) Wrong ((f) गलत) — All lines seem to come out of the shaded upper plate, so a surface around it has non-zero net flux — impossible for B. These are ELECTROSTATIC lines between a + plate and a − plate. Compare carefully with (e).
- (g) Wrong ((g) गलत) — Lines between two pole pieces cannot be perfectly straight up to the edges: some fringing (bulging out) is unavoidable, otherwise Ampere’s law is violated. True for electric lines too.
Original diagram drawn by Simple Learning Hub, based on NCERT Fig 5.6. Report a mistake