Exams › JEE Main › Physics
A long straight wire carries a current from A to B that is increasing in magnitude. A nearby conducting loop lies in the same plane, beside the wire. The induced current in the loop will
- have a direction such that its own field opposes the increasing flux of the wire
- have a direction such that its own field aids the increasing flux of the wire
- be zero because the wire and loop are coplanar
- oscillate between clockwise and anticlockwise
Correct answer: have a direction such that its own field opposes the increasing flux of the wire
Solution
The straight wire produces a magnetic field that threads the coplanar loop. As the current from A to B increases, the magnetic flux through the loop increases. By Lenz's law the induced current must flow so that its own magnetic field opposes this increase, i.e. it tries to maintain the original (smaller) flux. The exact clockwise/anticlockwise sense depends on which side of the wire the loop sits, but in all cases the induced current opposes the increasing flux. The current is steady (not oscillating) and is non-zero even though the wire and loop are coplanar.
Related JEE Main Physics questions
- A metallic ring is kept in a horizontal position, and a bar magnet is released so that it falls through the ring with its length aligned along the ring’s axis. The magnet’s acceleration while falling is
- A coil has resistance 10 Ω, and the magnetic flux linked with it changes with time according to ϕ = 4t² + 2t + 1 (in weber). The current induced in the coil at t = 1 s is
- Two coils are kept near one another. The mutual inductance of the coil pair depends on
- A conducting rod of length ℓ is attached to a string of length 2ℓ and is rotated on a horizontal table about the fixed end of the string with angular speed ω. If a uniform magnetic field B acts vertically through the region, what is the induced emf between the two ends of the rod?
- A pair of coils, each having N turns, has mutual inductance M henry. If the current in one coil changes from 1 ampere to zero in time t seconds, what is the induced emf per turn in the other coil, in volts?
- A boat travels straight toward the east in a place where Earth’s magnetic field is horizontal, points due north, and has magnitude 5.0 × 10⁻⁵ N A⁻¹ m⁻¹. A 2 m long vertical antenna is mounted on the boat. If the boat’s speed is 1.50 m s⁻¹, what emf is induced across the antenna wire?
⚔️ Practice JEE Main Physics free + battle 1v1 →