Electric Charges & Fields
Class 12 · Electric Charges & Fields
Infinite Line Charge
Radial E field perpendicular to a long charged wire. Falls as 1/r.
Key Notes
01
Field around an infinite straight charged line is radial (perpendicular to the line).
02
Magnitude depends only on perpendicular distance r — falls as 1/r (not 1/r²).
03
Use Gauss's law with a cylindrical Gaussian surface coaxial with the wire.
Formulas
Infinite line field
λ = charge per unit length.
Important Points
For a finite wire, integrate dE; the result depends on the angles subtended at the field point.
1/r falloff means line charges create longer-range fields than point charges.
Infinite Line Charge notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.