In Oersted’s experiment, deflection of magnetic needle produced due to current carrying wire

Options

A. remain constant with decrease In current
B. Increases with Increase In current
C. first Increases then decreases with Increase In current
D. not found in Oersted's experiment

Answer

### Step-by-Step Solution:

1. **Understanding Oersted’s Experiment**:
Oersted's experiment demonstrates the relationship between electricity and magnetism. When an electric current flows through a wire, it generates a magnetic field around it.

2. **Setting Up the Experiment**:
In the experiment, a straight current-carrying wire is placed parallel to a magnetic needle (compass). The magnetic needle has a north and south pole.

3. **Direction of Magnetic Field**:
The magnetic field generated by the current-carrying wire forms concentric circles around the wire. The direction of the magnetic field can be determined using the right-hand rule.

4. **Magnetic Field Formula**:
The magnetic field (B) at a distance (r) from a long straight current-carrying wire is given by the formula:
\[ B = \frac{\mu_0 I}{2 \pi r} \]
where \( \mu_0 \) is the permeability of free space and \( I \) is the current flowing through the wire.

5. **Effect on the Magnetic Needle**:
The magnetic field exerts a force on the magnetic needle. The force on the north pole of the needle will cause it to deflect. The deflection angle depends on the strength of the magnetic field.

6. **Relationship Between Current and Deflection**:
As the current (I) increases, the magnetic field (B) also increases, leading to a stronger force acting on the magnetic needle. Therefore, the deflection of the needle increases with an increase in current.

7. **Conclusion**:
Based on the relationship established, we can conclude that the deflection of the magnetic needle increases with an increase in the current flowing through the wire.

### Final Answer:
The deflection of the magnetic needle increases with an increase in current.