Question

Select the incorrect option regarding Lorentz force.

• A. In presence of electric field $\vec{E}(r)$ and magnetic field $\vec{B}(r)$, the force on a moving electric charge is:
  $\vec{F}=q[\vec{E}(r)+\vec{v}\times \vec{B}(r)]$
• B. The force due to magnetic field on a negative charge is opposite to that on a positive charge.
• C. The force due to magnetic field becomes zero when velocity and magnetic field are parallel or antiparallel.
• D. For a static charge the magnetic force is maximum.

Answer 1

Answer: (D)

In presence of electric field $\vec{E}(r)$ and magnetic field $\vec{B}(r)$, the force on a moving electric charge is:
$\vec{F}=q[\vec{E}(r)+\vec{v}\times \vec{B}(r)]$
If charge is not moving, then the magnetic force is zero.
Since ${\vec{F}}_m=q\vec{v}\times \vec{B}r$
As $\vec{v}=0$, for stationary charge
$\therefore {\vec{F}}_m=0$