Class 10 > Unit # 14: Electrostatics > Electric Field Intensity & Electric Field Lines

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Electrostatics - Electric Field and Field Lines

Q. Define Electric Field and Electric Field Lines. Draw electric field lines for (i) Positive charge (ii) Negative charge.

Electric Field

"The region or space around a charged body in which another test charge experiences an electrostatic force is called an electric field."

Electric Field Intensity

Electric field intensity ($\vec{E}$) at a point is defined as the electrostatic force ($\vec{F}$) experienced per unit positive test charge ($q_0$) placed at that point. Mathematically:

$\vec{E} = \frac{\vec{F}}{q_0}$

• Nature: Electric field intensity is a vector quantity.
• Direction: Its direction points radially outward if the source charge is positive (away from the charge) and radially inward if the source charge is negative (towards the charge).
• S.I. Unit: Newton per Coulomb ($\text{N/C}$ or $\text{V/m}$).

Electric Field Lines

"An electric field line (or line of force) is an imaginary smooth curve drawn in an electric field such that the tangent at any point on the curve gives the direction of the electric field intensity at that point."

Figure: Visualizing electric field lines for isolated positive and negative charges.

Key Properties of Electric Field Lines

• Field lines originate from a positive charge and terminate on a negative charge.
• The direction of the electric field at any point is found by drawing a tangent to the field line at that exact point.
• Electric field lines never intersect with each other, because an intersection would imply two different electric field directions at a single point, which is physically impossible.
• Lines of force do not originate or terminate abruptly in empty space surrounding a charge.

Field Line Configurations

1. (i) Positive Charge:
   For an isolated positive point charge, the electric field lines radiate strictly outward symmetrically in all directions.
2. (ii) Negative Charge:
   For an isolated negative point charge, the electric field lines point strictly inward symmetrically from infinity toward the charge.

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