A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region.

Question

A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected in the region such that its velocity is pointed along the direction of fields, then the electron:

Accepted Answer

1.  **Analyze Magnetic Force ($F_m$):** The magnetic force on a moving charge is given by $\vec{F}_m = q(\vec{v} 	imes \vec{B})$. Since the electron is projected along the direction of the magnetic field, the velocity vector $\vec{v}$ is parallel to the magnetic field vector $\vec{B}$ ($	heta = 0^\circ$). Therefore, $\vec{F}_m = qvB \sin(0^\circ) = 0$. The magnetic field exerts no force and causes no deflection.
2.  **Analyze Electric Force ($F_e$):** The electric force is given by $\vec{F}_e = q\vec{E}$. The electron carries a negative charge ($q = -e$). Since the electric field $\vec{E}$ acts in the same direction as the velocity, the force on the electron acts in the **opposite direction** to the field (and thus opposite to the velocity).
3.  **Conclusion:** The electric force acts as a retarding force opposing the motion. Consequently, the electron decelerates, and its speed decreases .

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