When the electric  current is passed through the wire from South [S] to North [N] direction and the wire is placed over [] the compass needle the compass needle, the compass needle get deflected towards West [W] direction 

Rule for finding the direction of deflection of magnetic needle:

When a magnetic needle is placed near a current-carrying conductor or a magnet, it experiences a force that causes it to deflect. The direction of this deflection can be determined by applying the following rule:

Fleming's left-hand rule:
Fleming's left-hand rule is used to determine the direction of the force acting on a current-carrying conductor placed in a magnetic field or the direction of deflection of a magnetic needle when placed near a current-carrying conductor.

The three fingers:
To apply Fleming's left-hand rule, three fingers of the left hand are used:

1. Thumb: The thumb represents the direction of the motion or force acting on the conductor or the magnetic needle.

2. Index finger: The index finger represents the direction of the magnetic field around the conductor or the magnet.

3. Middle finger: The middle finger represents the direction of the current flowing in the conductor.

The application of the rule:
To determine the direction of deflection of a magnetic needle, follow these steps:

1. Extend the thumb, index finger, and middle finger of the left hand perpendicular to each other, such that they are mutually perpendicular.

2. Align the thumb in the direction of motion or force that needs to be determined.

3. Orient the index finger in the direction of the magnetic field.

4. Adjust the middle finger in the direction of the current flowing through the conductor.

5. The direction in which the extended thumb points represents the direction of the deflection of the magnetic needle.

This rule can also be used to determine the direction of motion or force acting on a current-carrying conductor when the direction of the magnetic field and the direction of the current are known.

Example:
Let's consider an example where a magnetic needle is placed near a current-carrying conductor. If the direction of the magnetic field is from north to south and the direction of the current is from east to west in the conductor, the deflection of the magnetic needle can be determined using Fleming's left-hand rule as follows:

1. Align the thumb in the direction of deflection.

2. Orient the index finger from north to south, representing the magnetic field.

3. Adjust the middle finger from east to west, representing the direction of the current.

4. The direction in which the extended thumb points will indicate the direction of deflection of the magnetic needle.

By using this rule, the direction of deflection of a magnetic needle can be determined accurately in different situations involving current-carrying conductors and magnets.