An unsupported horizontal wire is to be prevented from falling under gravity using an external magnetic field. Wire carries current from North to South. The magnetic field should be directed towards

Options

A. south
B. north
C. east
D. west

Explanation

To solve the problem, we need to determine the direction of the external magnetic field required to prevent a horizontal wire carrying current from falling under the influence of gravity. The wire carries current from North to South.

### Step-by-Step Solution:

1. **Identify the Directions**:
- The wire is horizontal and carries current from North to South.
- We need to consider the direction of the gravitational force acting on the wire, which acts downwards (towards the Earth).

2. **Determine the Required Magnetic Force**:
- To prevent the wire from falling, the magnetic force acting on it must counteract the gravitational force. This means the magnetic force must act upwards (out of the plane of the wire).

3. **Apply Fleming's Left-Hand Rule**:
- Fleming's Left-Hand Rule states that if you align your thumb, index finger, and middle finger of your left hand at right angles to each other:
- The **thumb** represents the direction of the force (magnetic force).
- The **index finger** represents the direction of the magnetic field.
- The **middle finger** represents the direction of the current.

4. **Set the Directions**:
- Since the current is flowing from North to South, we can point the middle finger (current) downwards.
- The force (thumb) must point upwards (out of the paper) to counteract gravity.

5. **Determine the Direction of the Magnetic Field**:
- With the middle finger pointing down (current) and the thumb pointing up (force), the index finger will point towards the East.
- Therefore, the direction of the magnetic field must be towards the East.

### Conclusion:
The magnetic field should be directed towards the East.