A dip circle is at right angles to the magnetic meridian. What will be the apparent dip ?

Options

A. `0^(@) `
B. `30^(@) `
C. `60^(@)`
D. `90^(@)`

Explanation

To solve the problem of finding the apparent dip when a dip circle is at right angles to the magnetic meridian, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Setup**:
- A dip circle is a device used to measure the angle of dip (or inclination) of the Earth's magnetic field.
- The magnetic meridian is the plane that contains the magnetic field lines and the vertical component of the magnetic field.

2. **Identify Components of the Magnetic Field**:
- The Earth's magnetic field can be resolved into two components:
- **Vertical Component (BV)**: This is the component of the magnetic field acting vertically downwards.
- **Horizontal Component (BH)**: This is the component of the magnetic field acting horizontally.

3. **Position of the Dip Circle**:
- When the dip circle is at right angles to the magnetic meridian, it means the angle (α) between the dip circle's plane and the magnetic meridian is 90 degrees.

4. **Calculating the Horizontal Component in the Dip Circle's Plane**:
- The horizontal component of the magnetic field in the plane of the dip circle (BH') can be expressed as:
\[ BH' = BH \cdot \cos(\alpha) \]
- Since α = 90 degrees, we have:
\[ BH' = BH \cdot \cos(90^\circ) = BH \cdot 0 = 0 \]

5. **Resultant Magnetic Field in the Dip Circle's Plane**:
- The vertical component remains the same (BV = VV).
- Therefore, the resultant magnetic field (B) in the plane of the dip circle is purely vertical:
\[ B = \sqrt{(BH')^2 + (BV)^2} = \sqrt{0^2 + VV^2} = VV \]

6. **Finding the Apparent Dip**:
- The angle of dip (φ) in the dip circle's plane can be calculated using:
\[ \tan(\phi) = \frac{BV}{BH'} \]
- Since BH' = 0, this leads to:
\[ \tan(\phi) = \frac{VV}{0} \]
- This results in φ approaching infinity, which corresponds to:
\[ \phi = \frac{\pi}{2} \text{ or } 90^\circ \]

7. **Conclusion**:
- Thus, when the dip circle is at right angles to the magnetic meridian, the apparent dip is 90 degrees.

### Final Answer:
The apparent dip when the dip circle is at right angles to the magnetic meridian is **90 degrees**.

---