Exams › JEE Main › Physics

In figure (a) a solenoid's magnetic field, increasing into the page, induces an emf in a surrounding conducting loop that lights two bulbs A and B (in series around the loop). In figure (b) two points P and Q on the loop are connected by a short wire. After the short is inserted, what happens to the bulbs?

1. Bulb A goes out, bulb B gets brighter
2. Bulb B goes out, bulb A gets brighter
3. Bulb A goes out, bulb B gets dimmer
4. Bulb B goes out, bulb A gets dimmer

Correct answer: Bulb A goes out, bulb B gets brighter

Solution

Adding the short PQ provides a zero-resistance path that bypasses one bulb (A), so no current flows through it and it goes out. The remaining bulb B now carries the loop's induced emf across less total resistance, so it glows brighter. (The exact bulb depends on the figure; with A in the bypassed branch, A goes out and B brightens.)

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 →