To define the SI unit of electrical resistance, which is the Ohm, we can follow these steps:
### Step-by-Step Solution:
1. **Understanding Electrical Resistance**:
- Electrical resistance is a measure of the opposition to the flow of electric current in a conductor.
2. **Identifying the SI Unit**:
- The SI unit of electrical resistance is the Ohm, symbolized by the Greek letter Omega (Ω).
3. **Defining One Ohm**:
- One Ohm can be defined in terms of voltage and current. According to Ohm's Law, the relationship between voltage (V), current (I), and resistance (R) is given by the formula:
\[
R = \frac{V}{I}
\]
- Here, R is the resistance in Ohms, V is the voltage in Volts, and I is the current in Amperes.
4. **Specific Definition of One Ohm**:
- Therefore, one Ohm is defined as the resistance of a conductor when a potential difference of 1 Volt is applied across it, causing a current of 1 Ampere to flow through it.
- Mathematically, this can be expressed as:
\[
1 \, \text{Ohm} = \frac{1 \, \text{Volt}}{1 \, \text{Ampere}}
\]
5. **Conclusion**:
- Thus, the correct definition of one Ohm is that it is equal to 1 Volt per 1 Ampere, or in terms of units:
\[
1 \, \text{Ohm} = 1 \, \text{Volt} \cdot \text{Ampere}^{-1}
\]
### Final Answer:
The SI unit of electrical resistance, the Ohm, is defined as:
\[
1 \, \text{Ohm} = 1 \, \text{Volt} \cdot \text{Ampere}^{-1}
\]
