### 1. SI Unit of Magnetic Flux
The SI unit of magnetic flux is the **weber**.
*   **Symbol**: $\text{Wb}$

### 2. Namesake
The unit is named after the German physicist **Wilhelm Eduard Weber** (1804–1891). He made significant contributions to the study of electromagnetism, including the development of the first electromagnetic telegraph and the definition of electrical units.

### 3. Expression in SI Base Units
To express the weber in SI base units, we can derive it from the definition of magnetic flux ($\Phi_B$) and Faraday's law of induction.

**Step-by-Step Derivation:**
1.  **Definition**: Magnetic flux is defined as the product of the magnetic field ($B$) and the area ($A$) perpendicular to the field:
    $$ \Phi_B = B \cdot A $$
    Therefore, $1 \, \text{Wb} = 1 \, \text{T} \cdot \text{m}^2$ (where $\text{T}$ is the tesla).

2.  **Analyze the Tesla ($\text{T}$)**: The tesla is the unit of magnetic flux density. It can be derived from the Lorentz force law ($F = qvB$), where $F$ is force, $q$ is charge, and $v$ is velocity.
    $$ B = \frac{F}{q \cdot v} $$
    *   Force ($F$) in base units: $\text{kg} \cdot \text{m} \cdot \text{s}^{-2}$ (Newtons)
    *   Charge ($q$) in base units: $\text{A} \cdot \text{s}$ (Coulombs)
    *   Velocity ($v$) in base units: $\text{m} \cdot \text{s}^{-1}$

    Substituting these into the equation for $B$:
    $$ 1 \, \text{T} = \frac{\text{kg} \cdot \text{m} \cdot \text{s}^{-2}}{(\text{A} \cdot \text{s}) \cdot (\text{m} \cdot \text{s}^{-1})} = \frac{\text{kg} \cdot \text{m} \cdot \text{s}^{-2}}{\text{A} \cdot \text{m}} = \text{kg} \cdot \text{s}^{-2} \cdot \text{A}^{-1} $$

3.  **Calculate the Weber ($\text{Wb}$)**:
    Now substitute the base units of the tesla back into the flux equation ($\text{Wb} = \text{T} \cdot \text{m}^2$):
    $$ 1 \, \text{Wb} = (\text{kg} \cdot \text{s}^{-2} \cdot \text{A}^{-1}) \cdot \text{m}^2 $$
    $$ 1 \, \text{Wb} = \text{kg} \cdot \text{m}^2 \cdot \text{s}^{-2} \cdot \text{A}^{-1} $$

    *Alternative derivation via Voltage*: Since $1 \, \text{Wb} = 1 \, \text{V} \cdot \text{s}$ (from Faraday's law $\mathcal{E} = -d\Phi/dt$), and $1 \, \text{V} = 1 \, \text{J}/\text{C} = (\text{kg} \cdot \text{m}^2 \cdot \text{s}^{-2}) / (\text{A} \cdot \text{s})$, multiplying by seconds yields the same result.

### Final Conclusion

*   **SI Unit**: Weber ($\text{Wb}$)
*   **Named After**: Wilhelm Eduard Weber
*   **SI Base Units**: $\text{kg} \cdot \text{m}^2 \cdot \text{s}^{-2} \cdot \text{