The formula for calculating the magnetic field strength of a coil is μ₀NlI/R, where μ₀ is the permeability of free space (4π x 10⁻⁷), N is the number of turns, l is the length of the coil, I is the current, and R is the radius of the coil.
The more turns a coil has, the stronger the magnetic field will be. This is because each turn contributes to the overall magnetic field, so increasing the number of turns will increase the strength of the field.
The unit of measurement for magnetic field strength is tesla (T) in the SI system. Another commonly used unit is gauss (G), where 1 T = 10,000 G.
The radius of a coil has an inverse relationship with the magnetic field strength. This means that as the radius increases, the magnetic field strength decreases. In other words, a smaller radius will result in a stronger magnetic field, and a larger radius will result in a weaker magnetic field.
The direction of the magnetic field in a coil is determined by the right-hand rule. If you point your right thumb in the direction of the current (from positive to negative), the curl of your fingers will indicate the direction of the magnetic field. In this case, the magnetic field will be directed counterclockwise when viewed from above the coil.