Which of the following is NOT true about the Lorentz force?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → It consists of the vector product of the velocity of the moving particle and the electric field.
The Lorentz force on a charge \( q \) moving with velocity \( \vec{v} \) in electric and magnetic fields is \( \vec{F}=q\,[\vec{E}+\vec{v}\times\vec{B}] \). It has an electric part \( q\vec{E} \) and a magnetic part \( q\,(\vec{v}\times\vec{B}) \).
Option (1) It consists of the vector product of the velocity of the moving particle and the electric field. — Not true about the Lorentz force. The vector product in the force is \( \vec{v}\times\vec{B} \), of the velocity and the magnetic field. The electric field enters only as \( q\vec{E} \), with no vector product.
Option (2) In the absence of any magnetic field, the Lorentz force still exists. — True about the Lorentz force. With \( \vec{B}=0 \), the electric part \( q\vec{E} \) remains, so a charge in an electric field still feels a force.
Option (3) The Lorentz force is zero for a neutron. — True about the Lorentz force. Both parts are proportional to the charge \( q \), and a neutron has no charge.
NCERT (2026-27):
Magnetic Field, Lorentz Force – “(ii) The magnetic force q [ v × B ] includes a vector product of velocity and magnetic field.”