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In an electromechanical energy conversion device, the coupling field on the (i) electrical side is associated with emf and current (ii) electrical side is associated with torque and speed (iii) mechanical side is associated with emf and current (iv) mechanical side is associated with torque and speed From the above, the correct statements are

A) (i) & (ii)

B) (iii) & (iv)

C) (i) and (iv)

D) (ii) & (iii)

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalMachine

Option C

(i) and (iv)

Quick Summary:

In an electromechanical energy conversion device, energy transfers between electrical and mechanical systems through a coupling magnetic or electric field. The electrical terminal variables are voltage (induced electromotive force, emf $e$ ) and electrical current ( $i$ ), while the mechanical terminal variables are torque ( $T$ ) or force ( $F$ ) and rotational speed ( $omega$ ) or velocity ( $v$ ).

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$P_e = e \cdot i$ — Electrical power input/output

$P_m = T \cdot \omega$ — Mechanical power output/input

$e = N \frac{d\Phi}{dt}$ — Induced electromotive force (Faraday's Law)

$T_e = \frac{1}{2} i^2 \frac{dL}{d\theta}$ — Developed electromagnetic torque

⚙️ Working Principle

The coupling magnetic field links the electrical port and mechanical port. On the electrical side, power is given by $P_e = e \cdot i$ , associated with emf and current. On the mechanical side, power is given by $P_m = T \cdot \omega$ , associated with electromagnetic torque and rotational speed.

📌 Key Points

▸
Electrical variables associated with energy conversion are electromotive force (emf) and current.
▸
Mechanical variables associated with energy conversion are torque (or force) and speed (or linear velocity).
▸
The coupling magnetic field stores energy and acts as a medium to transfer power between the electrical and mechanical systems.

✅ Advantages

▸
High efficiency in conversion via magnetic coupling field compared to electric field coupling.
▸
Bidirectional power flow allows operation as both generator and motor.

❌ Disadvantages / Limitations

▸
Energy losses occur in the coupling medium due to hysteresis, eddy currents, and field saturation.
▸
Requires magnetic materials which contribute to total mass and weight.

🛠️ Applications / Uses

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Electric motors (converting electrical power into mechanical torque and speed).
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Electric generators (converting mechanical torque and speed into electrical voltage and current).

🔄 Comparison Table

Feature	Electrical Side	Mechanical Side
Associated Variables	EMF ( $e$ ) & Current ( $i$ )	Torque ( $T$ ) & Speed ( $ω$ )
Power Equation	$P_e = e \cdot i$	$P_m = T \cdot \omega$
Energy Storage/Transfer Domain	Electrical terminals / Circuits	Shaft / Moving Mechanical Parts

📄 Additional Information

▸
Statement (ii) incorrectly attributes torque and speed to the electrical side.
▸
Statement (iii) incorrectly attributes emf and current to the mechanical side.
▸
Therefore, statements (i) and (iv) are the only correct statements, making Option C correct.

📊 Diagram / Illustration

✅

C is correct — statement (i) accurately pairs the electrical side with emf and current, while statement (iv) correctly pairs the mechanical side with torque and speed.

Core Concepts Used

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Electromechanical Energy Conversion Coupling Magnetic Field Terminal Variables

💡 EXAM TIP

Remember that energy balance in an electromechanical system always obeys $dW_{elec} = dW_{mech} + dW_{field} + dW_{loss}$ , where electrical inputs ( $e \cdot i \, dt$ ) and mechanical outputs ( $T \cdot \omega \, dt$ ) interact directly through field storage.

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