In a certain region, uniform electric field E and magnetic field B are present in the opposite direction. A particle of mass m and of charge q enters in this region with a velocity v at an angle θ from the magnetic field. The time after which the speed of the particle would be minimum is equal to

Question

In a certain region, uniform electric field E and magnetic field B are present in the opposite direction. A particle of mass m and of charge q enters in this region with a velocity v at an angle θ from the magnetic field. The time after which the speed of the particle would be minimum is equal to, 2 π m B q, m v sin ⁡ θ q E, m v cos ⁡ θ q E, m v q E

MARKS App · Accepted Answer

The charges experiences a retarding force F = q E along x-axis Retardation = q E m . It is clear that the speed of the particle will be minimum when its component of velocity is along the direction of electric field. Then, using the equation of motion, v = u + a t ⇒ 0 = v cos ⁡ θ - q E m t ⇒ t = m v cos ⁡ θ q E

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