A long solenoid has a diameter of 11.0 cm. When a current i exists in its windings, a uniform magnetic field of magnitude b=33.7 mT. What is the expression for the magnetic field inside the solenoid?
a) b = (4 * π * 10⁽⁻⁷⁾* i) / (π * r²)
b) b = (4 * π * 10⁽⁻⁷⁾ * i) / (2 * π * r)
c) b = (4 * π * 10⁽⁻⁷⁾ * i) / (π * r)
d) b = (2 * π * 10⁽⁻⁷⁾ * i) / (π * r²)