The electric field of an infinite line of charge with linear charge density λ at perpendicular distance r is
A{'text': 'E = λ / (ε₀ r²)', 'label': 'A'}
B{'text': 'E = λ / (4π ε₀ r²)', 'label': 'B'}
C{'text': 'E = λ r / (2π ε₀)', 'label': 'C'}
D{'text': 'E = λ / (2π ε₀ r)', 'label': 'D'}
Answer & Solution
Correct answer: D. {'text': 'E = λ / (2π ε₀ r)', 'label': 'D'}
1. Apply Gauss's law with a cylindrical Gaussian surface coaxial with the line.
2. Field E is radial and uniform on the cylinder side, zero on end caps.
3. Flux = E × 2π r L = λL / ε₀, giving E = λ / (2π ε₀ r).
4. Field falls off as 1/r, characteristic of the line-charge geometry.
_Source: NCERT Class 12 Physics, Ch 1 "Electric Charges and Fields", §1.10_
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