The force between two parallel wires carrying currents has been used to define

Options

A. ampere
B. coulomb
C. volt
D. watt

Explanation

To solve the question, "The force between two parallel wires carrying currents has been used to define," we need to analyze the options provided and understand the relationship between current and force in parallel wires.

### Step-by-Step Solution:

1. **Understanding the Concept**:
The force between two parallel wires carrying electric currents is a fundamental concept in electromagnetism. When two parallel wires carry currents, they exert a force on each other due to the magnetic fields created by the currents.

2. **Identifying the Options**:
The options provided are:
- Option 1: Ampere
- Option 2: Coulomb
- Option 3: Volt
- Option 4: Watt

3. **Analyzing the Definition of Ampere**:
The ampere is defined as the current that, when flowing through two parallel conductors placed one meter apart in a vacuum, produces a force of 2 × 10^(-7) newtons per meter of length between the wires.

4. **Using the Formula for Force**:
The formula for the force per unit length (F/L) between two parallel wires carrying currents I1 and I2 is given by:
\[ \frac{F}{L} = \frac{\mu_0 I_1 I_2}{2\pi d} \]
where:
- \( F \) is the force between the wires,
- \( L \) is the length of the wires,
- \( \mu_0 \) is the permeability of free space (\( 4\pi \times 10^{-7} \, \text{T m/A} \)),
- \( d \) is the distance between the wires.

5. **Substituting Values**:
For the definition of 1 ampere, we can set \( I_1 = I_2 = 1 \, \text{A} \) and \( d = 1 \, \text{m} \):
\[ \frac{F}{L} = \frac{4\pi \times 10^{-7} \times 1 \times 1}{2\pi \times 1} \]
Simplifying this gives:
\[ \frac{F}{L} = \frac{4 \times 10^{-7}}{2} = 2 \times 10^{-7} \, \text{N/m} \]

6. **Conclusion**:
Since the force between two parallel wires carrying currents is used to define the ampere, the correct answer to the question is **Option 1: Ampere**.