A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its north tip down at `60^(@)` with the horizontal.The horizontal component of the earth's magnetic field at the place is known to be `0.4G`.Determine the magnitude of the earth's magnetic field at the place.

Explanation

To solve the problem, we need to determine the magnitude of the Earth's magnetic field (R) given the angle of the magnetic needle (δ) and the horizontal component of the Earth's magnetic field (H).

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Angle of the magnetic needle (δ) = 60 degrees
- Horizontal component of the Earth's magnetic field (H) = 0.4 G

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