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Motion of a charge in electric and magnetic fields
Concepts tested here
- Lorentz force
All Questions
2011 AIPMT-PRE 1 question
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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 electronMagnetic force: $\vec{F}_m = q(\vec{v}\times\vec{B})$. The velocity is parallel to $\vec{B}$, so $\vec{v}\times\vec{B} = 0$ and there is no magnetic force; the electron does not turn.
Electric force: $\vec{F}_e = q\vec{E} = -e\vec{E}$. Since the electron has negative charge, this force is opposite to $\vec{E}$.
The velocity is along $\vec{E}$, so the electric force is opposite to the velocity.
The electron is therefore retarded along its line of motion.
Hence its speed will decrease.