Which, among the following is the correct expression for an electric field?

Question

Examoogle · Accepted Answer

$E = \frac{F}{Q}$

Explanation: The electric field ($E$) is a vector quantity that represents the force exerted per unit charge placed at a specific point in space. It describes the influence of an electric charge on its surrounding medium, defined as the ratio of the electrostatic force to the charge magnitude.

Working Principle: When a test charge $q$ is placed in an electric field created by a source charge, it experiences a force $F$. The electric field intensity is defined as the limit of the force acting on a vanishingly small test charge to avoid disturbing the field, expressed as $E = \frac{F}{Q}$. The direction of $E$ is conventionally defined as the direction of the force acting on a positive unit test charge.

Key Formulas: $E = \frac{F}{Q}$ — definition of electric field intensity; $F = qE$ — force experienced by a charge $q$ in field $E$

Key Points: The SI unit of electric field is Newtons per Coulomb (N/C) or Volts per meter (V/m).; Electric field lines originate from positive charges and terminate at negative charges.; Electric field is a vector field; it possesses both magnitude and direction.

Advantages: Allows for the determination of force on any charge placed in the field.; Essential for understanding electrostatic potential and capacitance.

Disadvantages: Superposition of fields from multiple charges requires vector addition which can be mathematically complex.; Does not account for relativistic effects in high-velocity scenarios.

Applications: Design of capacitors and dielectric materials.; Analysis of electron beam motion in vacuum tubes and cathode ray tubes.

Additional Info: The test charge Q is conceptually assumed to be small enough not to influence the source charge distribution.. Options A, B, and D are incorrect as they represent incorrect algebraic relationships between force, charge, and field strength.

Answer: C is correct — The electric field strength is defined as the force per unit charge, given by the expression $E = \frac{F}{Q}$.

Exam Tip: Remember that Electric Field intensity is analogous to Gravitational Field intensity (Force/Mass); use this analogy to recall definitions easily.

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