Home › UP Board Class 12 › Physics › Moving Charges and Magnetism › An electron enters a uniform magnetic field B at…
An electron enters a uniform magnetic field B at angle θ to B with speed v. The pitch of its helical path is
A2πm v sin θ / (eB)
B2πm v cos θ / (eB)
C2πm v / (eB)
Dm v cos θ / (eB)
Answer & Solution
Correct answer: B. 2πm v cos θ / (eB)
1. Decompose velocity: parallel v∥ = v cos θ and perpendicular v⊥ = v sin θ.
2. The perpendicular component drives circular motion with period T = 2πm/(eB).
3. The parallel component moves the centre of the circle linearly at v cos θ.
4. Pitch = distance moved along the axis in one period = v cos θ · T = 2πm v cos θ/(eB).
_Source: NCERT Class 12 Physics Ch 4 "Moving Charges and Magnetism", §4.3_
Related questions
An electron and a proton enter a magnetic field with the same kinetic energy, perpendiculaA galvanometer is converted into an ammeter of higher range by connecting:The work done by a static magnetic force on a moving charge is:Magnetic field at a point on the axis of a circular loop, far from the loop (distance x ≫ The dimensional formula of the magnetic field B (in SI units of tesla) is:A cyclotron of magnetic field B accelerates positive charges of mass m, charge q. The cyclTorque on a magnetic dipole (current loop) of moment m placed in a uniform field B at anglTwo long parallel wires carry currents I₁ and I₂ in the SAME direction, separated by dista