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

Options

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

Answer

To solve the question regarding the definition of the force between two parallel wires carrying currents, we can follow these steps:

### 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 Parameters**:
- Let the currents in the two wires be \( I_1 \) and \( I_2 \).
- The distance between the two wires is \( r \).
- The force per unit length between the two wires is given by the formula:
\[ F/L = \frac{\mu_0 I_1 I_2}{2\pi r} \]
where \( \mu_0 \) is the permeability of free space.

3. **Setting the Values**: For the purpose of defining the ampere:
- Set \( I_1 = 1 \, \text{A} \) and \( I_2 = 1 \, \text{A} \).
- Set the distance \( r = 1 \, \text{m} \).

4. **Calculating the Force**: Substitute the values into the formula:
\[ F/L = \frac{\mu_0 \cdot 1 \cdot 1}{2\pi \cdot 1} \]
- Using \( \mu_0 = 4\pi \times 10^{-7} \, \text{T m/A} \):
\[ F/L = \frac{4\pi \times 10^{-7} \cdot 1 \cdot 1}{2\pi \cdot 1} = \frac{4 \times 10^{-7}}{2} = 2 \times 10^{-7} \, \text{N/m} \]

5. **Defining the Ampere**: The ampere is defined based on the force experienced between two parallel wires carrying a current of 1 ampere each, 1 meter apart, resulting in a force of \( 2 \times 10^{-7} \, \text{N/m} \).

6. **Conclusion**: Thus, the force between two parallel wires carrying currents has been used to define the unit of electric current, which is the **ampere**.

### Final Answer:
The force between two parallel wires carrying currents has been used to define **ampere**.

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