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Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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ElectricalElectromagnetics Field Theory
PrevNext

For zero electric potential, electric field intensity is

A

000

B

111

C

dAdt\frac{dA}{dt}dtdA​

D

−dAdt-\frac{dA}{dt}−dtdA​

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalElectromagnetics Field Theory
Option D

−dAdt-\frac{dA}{dt}−dtdA​

Quick Summary:

In electromagnetic theory, the electric field intensity E\mathbf{E}E is related to the scalar electric potential VVV and the magnetic vector potential A\mathbf{A}A through the relation E=−∇V−∂A∂t\mathbf{E} = -\nabla V - \frac{\partial \mathbf{A}}{\partial t}E=−∇V−∂t∂A​. When the electric scalar potential VVV is zero, the electric field is determined entirely by the time-varying magnetic vector potential.

⚙️TETechnical SolutionConcept & Principle
💡 Explanation

In electromagnetic theory, the electric field intensity E\mathbf{E}E is related to the scalar electric potential VVV and the magnetic vector potential A\mathbf{A}A through the relation E=−∇V−∂A∂t\mathbf{E} = -\nabla V - \frac{\partial \mathbf{A}}{\partial t}E=−∇V−∂t∂A​. When the electric scalar potential VVV is zero, the electric field is determined entirely by the time-varying magnetic vector potential.

🔢 Key Formulas

E=−∇V−∂A∂t\mathbf{E} = -\nabla V - \frac{\partial \mathbf{A}}{\partial t}E=−∇V−∂t∂A​ — General definition of Electric Field

E=−∂A∂t\mathbf{E} = -\frac{\partial \mathbf{A}}{\partial t}E=−∂t∂A​ — Induced Electric Field for zero scalar potential

⚙️ Working Principle

According to Faraday's Law, a time-varying magnetic field induces an electric field. The total electric field is the sum of the conservative field (derived from the gradient of potential VVV) and the non-conservative, time-varying induced field (derived from the vector potential A\mathbf{A}A). When V=0V=0V=0, E=−∂A∂t\mathbf{E} = -\frac{\partial \mathbf{A}}{\partial t}E=−∂t∂A​, which represents the electromotive force induced by changing magnetic flux density.

📌 Key Points
  • ▸

    Electric potential VVV relates to electrostatic fields (∇V\nabla V∇V).

  • ▸

    Time-varying magnetic vector potential A\mathbf{A}A gives rise to induced non-conservative electric fields.

  • ▸

    The negative sign is a consequence of Lenz's Law, opposing the change in magnetic flux.

✅ Advantages
  • ▸

    Explains non-conservative field behavior

  • ▸

    Provides a unified framework for Maxwell's Equations

❌ Disadvantages / Limitations
  • ▸

    Requires knowledge of vector calculus

  • ▸

    Abstract nature of vector potential A\mathbf{A}A

🛠️ Applications / Uses
  • ▸

    Inductors and transformers

  • ▸

    Wave propagation studies

  • ▸

    Electromagnetic compatibility design

📄 Additional Information
  • ▸

    In static fields, A\mathbf{A}A is constant, making ∂A∂t=0\frac{\partial \mathbf{A}}{\partial t} = 0∂t∂A​=0, leading to E=−∇V\mathbf{E} = -\nabla VE=−∇V.

  • ▸

    Option A (0) is only true if both the potential and magnetic field are constant or zero.

📊 Diagram / Illustration
Electric Field RelationshipE = -∇ V - frac{∂A}{∂ t}For V=0, E = -frac{∂A}{∂ t}
✅

D is correct — The electric field intensity is equal to the negative time rate of change of the magnetic vector potential when scalar potential is zero.

Core Concepts Used
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Faraday's Law of Induction Magnetic Vector Potential Electromagnetic Field Theory
💡 EXAM TIP

Remember that E\mathbf{E}E is always defined by the scalar and vector potentials; always look for time-dependence (∂/∂t\partial / \partial t∂/∂t) in EM questions involving dynamic fields.

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