The strength of the magnetic field created by a current-carrying coil can be ______ by increasing the number of turns in it.

The magnetic field due to a current-carrying coil is directly proportional to the number of turns in the coil. 

The magnetic field in the center of a circular coil is calculated as follows:

$B=\frac{{\mu }_{0}nI}{2R}$

Where B= magnetic field is in the center of the coil.

 ${\mu }_0$ is the permeability of free space $=4\pi \times {10}^{-7}$, I is current, and the radius of the circular coil is R.

Since the magnetic field of a current-carrying coil is directly proportional to the number of turns in it, the strength of the magnetic field increases if we increase the number of turns.