An electron moves straight inside a charged parallel plate capacitor of uniform charge density. The space between the plates is filled with uniform magnetic field of intensity \(B ,\) as shown in the figure, Neglecting effect of gravity, the time of straight line motion of the electron in the capacitor is

A \(\frac{\sigma }{{{\varepsilon _0}lB}}\)
B \(\frac{{{\varepsilon _0}B}}{\sigma }\)
C \(\;\frac{\sigma }{{{\varepsilon _0}B}}\)
D \(\;\frac{{{\varepsilon _0}lB}}{\sigma }\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(\;\frac{{{\varepsilon _0}lB}}{\sigma }\)

Step-by-step Solution

Detailed explanation

\(F _{ E }= F _{ B }\) \(eE = evB\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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