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When a proton is released from rest in a room, it starts with an initial acceleration a₀ towards west. When it is projected towards north with a speed v₀, it moves with an initial acceleration 3a₀ towards west. The electric and magnetic fields in the room are respectively:
- ma₀ west, 2ma₀ down
- ma₀ east, 3ma₀ up
- ma₀ east, 3ma₀ down
- ma₀ west, 2ma₀ up
Correct answer: ma₀ east, 3ma₀ down
Solution
The proton's initial acceleration towards the west when at rest indicates an electric field pointing west. When the proton is projected north, the additional acceleration due to the magnetic force suggests a magnetic field pointing down. Using the Lorentz force equation, the electric field is ma₀ east, and the magnetic field is 3ma₀ down.
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