Consider a current carrying wire (current I) in the shape of a circle. Note that as the current progresses along the wire, the direction of `vecJ` (current density) changes in an exact manner, while the current I remains unaffected. The agent that is essentially responsible for is

Options

A. source of e.mf.
B. electric field produced by charges accumulated on the surface of wire.
C. the charges just behind a given segment of wire which push them just right way by repulsion
D. the charges just behind a given segment of wire which push them just right way by repulsion

Answer

To solve the question regarding the current-carrying wire in the shape of a circle, we need to analyze the behavior of current density (J) and current (I) in this specific configuration.

### Step-by-Step Solution:

1. **Understanding Current and Current Density**:
- Current (I) is defined as the flow of electric charge and is a scalar quantity. It does not have a direction, only a magnitude.
- Current density (J) is defined as the current per unit area and is a vector quantity. It has both magnitude and direction.

2. **Current Flow in a Circular Wire**:
- When a current flows through a wire shaped in a circle, the flow of positive charges (or conventional current) moves along the wire.
- As the positive charges move, the direction of the current density vector (J) changes continuously due to the circular path of the wire.

3. **Behavior of Current Density (J)**:
- The direction of J changes at every point along the circular wire, as it is tangent to the wire at each point.
- Despite the changing direction of J, the total current (I) flowing through the wire remains constant. This is because the amount of charge passing through any cross-section of the wire per unit time does not change.

4. **Role of Electric Field**:
- The electric field produced by the charges in the wire is responsible for maintaining the flow of current.
- The electric field is directed along the wire, and it influences the movement of charges, thus affecting the direction of J.

5. **Conclusion**:
- The agent responsible for the continuous change in the direction of J while keeping the current I constant is the electric field produced by the charges accumulated on the surface of the wire.

### Final Answer:
The agent that is essentially responsible for the changing direction of current density (J) while the current (I) remains unaffected is the **electric field produced by the charges accumulated on the surface of the wire**.