Volt-sec is the unit of which physical quantity?

Answer

To determine the physical quantity represented by the unit "volt-second," we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Volt**:
- The unit of electric potential difference is the volt (V). It is defined as one joule per coulomb (1 V = 1 J/C).

2. **Understand the Definition of Magnetic Flux**:
- Magnetic flux (Φ) is defined as the product of the magnetic field (B) and the area (A) through which the field lines pass, taking into account the angle (θ) between the field lines and the normal to the surface. The unit of magnetic flux is the weber (Wb).

3. **Relate Volt to Magnetic Flux**:
- According to Faraday's Law of Electromagnetic Induction, the induced electromotive force (emf) (E) in a circuit is proportional to the rate of change of magnetic flux through the circuit:
\[ E = -\frac{d\Phi}{dt} \]
- Here, E is measured in volts (V), and \(\Phi\) is the magnetic flux measured in webers (Wb).

4. **Rearranging the Equation**:
- Rearranging the equation gives:
\[ d\Phi = -E \cdot dt \]
- This indicates that the change in magnetic flux (dΦ) is equal to the induced emf (E) multiplied by the change in time (dt).

5. **Units of Each Quantity**:
- From the equation \(d\Phi = E \cdot dt\):
- The unit of emf (E) is volts (V).
- The unit of time (dt) is seconds (s).
- Therefore, the unit of magnetic flux (dΦ) can be expressed as:
\[ \text{Unit of } d\Phi = \text{Unit of } E \cdot \text{Unit of } dt = \text{volt} \cdot \text{second} = \text{volt-second} (V \cdot s) \]

6. **Conclusion**:
- Thus, we conclude that the unit "volt-second" is the unit of magnetic flux.

### Final Answer:
The unit "volt-second" is the unit of **magnetic flux**.

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