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
AIPMT 2011, Medium
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Force on electron due to electric field,
$\vec{F}_{E}=-e \vec{E}$
Force on electron due to magnetic field,
$\vec{F}_{B}=-e(\vec{v} \times \vec{B})=0$
since $\bar{v}$ and $\vec{B}$ are in the same direction.
Total force on the electron,
$\vec{F}=\vec{F}_{E}+\vec{F}_{B}=-e \vec{E}$
Electric field opposes the motion of the electron, hence speed of the electron will decrease.
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