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A uniform electric field E=(8m)/e V m⁻¹ is created between two parallel plates of length 1 m (where m is the mass of the electron and e the magnitude of its charge). An electron enters the field symmetrically between the plates with a speed of 2 m s⁻¹. The angle of deviation θ of the path of the electron as it comes out of the field will be

Asked in JEE Main 28th July 2nd Shift 2022 · Deflection and projectile motion

Figure: Deflection and projectile motion
Answer: (2) tan⁻¹(2)

Step-by-step solution

The electric force on the electron is transverse, so the horizontal speed stays vₓ=2 m s⁻¹.

Transverse acceleration a=(eE)/m=e/m·(8m)/e=8 m s⁻².

Time inside the plates: t=L/(vₓ)=1/2=0.5 s.

Transverse speed on exit: v_y=at=8×0.5=4 m s⁻¹.

tan θ=(v_y)/(vₓ)=4/2=2, so θ=tan⁻¹(2).

Why the other options are wrong

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