Match List-I with List-II
| List-I | List-II |
| (A) When initial velocity of a charged particle is parallel to a uniform magnetic field, it executes a _______. | (I) Circular path |
| (B) When initial velocity of a charged particle is perpendicular to a uniform magnetic field it executes a _______. | (II) Helical path |
| (C) When initial velocity of a charged particle is inclined with respect to the direction of a uniform magnetic field, it executes a _______. | (III) Straight path |
| (D) When initial velocity of a charged particle is perpendicular to an electric field, it executes a _______. | (IV) Parabolic path |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) – (III), (B) – (I), (C) – (II), (D) – (IV)
The magnetic force \( \vec{F} = q\,\vec{v} \times \vec{B} \) is always perpendicular to the velocity; it changes the direction of motion but not the speed.
(A) When initial velocity of a charged particle is parallel to a uniform magnetic field, it executes a _______. — this matches (III) Straight path. \( F = qvB\sin 0^\circ = 0 \), so the particle moves on undeflected.
(B) When initial velocity of a charged particle is perpendicular to a uniform magnetic field it executes a _______. — this matches (I) Circular path. The force qvB acts as a centripetal force.
\( \displaystyle r = \frac{mv}{qB} \)
(C) When initial velocity of a charged particle is inclined with respect to the direction of a uniform magnetic field, it executes a _______. — this matches (II) Helical path. The component along the field is unaffected while the perpendicular component gives circular motion; together they give a helix.
(D) When initial velocity of a charged particle is perpendicular to an electric field, it executes a _______. — this matches (IV) Parabolic path. A constant acceleration qE/m along the field with constant velocity across it gives a parabola, like a horizontally projected body under gravity.
NCERT (2026-27):
Magnetic Field, Lorentz Force – “… The vector product makes the force due to magnetic field vanish (become zero) if velocity and magnetic field are parallel or anti-parallel.”
Motion in a Magnetic Field – “… The particle will describe a circle if v and B are perpendicular to each other (Fig. 4.5). If velocity has a component along B, this component remains unchanged as the motion along the magnetic field will not be affected by the magnetic field. The motion in a plane perpendicular to B is as before a circular one, thereby producing a helical motion (Fig. 4.6).”