Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

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:

will turn towards right of direction of motion

will turn towards left of direction of motion

speed will decrease

speed will increase

Step-by-Step Solution

Analyze Magnetic Force ( $F_m$ ): The magnetic force on a moving charge is given by $\vec{F}_m = q(\vec{v} \times \vec{B})$ . Since the electron is projected along the direction of the magnetic field, the velocity vector $\vec{v}$ is parallel to the magnetic field vector $\vec{B}$ ( $\theta = 0^\circ$ ). Therefore, $\vec{F}_m = qvB \sin(0^\circ) = 0$ . The magnetic field exerts no force and causes no deflection.
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).
Conclusion: The electric force acts as a retarding force opposing the motion. Consequently, the electron decelerates, and its speed decreases .

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