The intensity of the magnetic field is 
Explanation:
According to Faraday's Law, the magnitude of the induced electromotive force (emf) in the coil corresponds to the rate of flux change that links through the coil:
(1)
where
N = 505 represents the number of turns in the coil
is the variation in magnetic flux through the coil
indicates the time interval

Rotating the coil from perpendicular to parallel alignment with the Earth's magnetic field results in the final flux equaling zero, making the magnitude of flux change simply the initial flux:

where
B denotes the intensity of the magnetic field
A signifies the area of the coil
represents the angle between the normal to the coil and the field
The area of the coil can be expressed as

where
outlines its radius
By substituting all values into equation (1) and solving for B, we obtain:

For further reading on magnetic fields: