Exams › JEE Main › Physics
The radius of a single-turn circular coil shrinks steadily at 10⁻² m/s in a constant uniform magnetic field of 10⁻³ Wb/m² directed perpendicular to the coil's plane. Find the radius of the coil at the instant the induced emf is 1 microvolt.
- 5/pi cm
- 2/pi cm
- 3/pi cm
- 4/pi cm
Correct answer: 5/pi cm
Solution
Flux phi = B*pi*r². Magnitude of induced emf = B*2*pi*r*|dr/dt|. Setting this equal to 1e-6 V: r = emf/(B*2*pi*|dr/dt|) = 1e-6/(1e-3 * 2*pi * 1e-2) = 1e-6/(2*pi*1e-5) = 0.05/pi m = 5/pi cm.
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 →