Define magnetic flux and magnetic flux density.

• Magnetic Flux ($\Phi$): A measure of the total number of magnetic field lines passing through a given area. It is a scalar quantity, measured in Webers (Wb).
• Magnetic Flux Density ($B$): The strength of a magnetic field, defined as the magnetic flux per unit area perpendicular to the direction of the magnetic flux. It is a vector quantity, measured in Teslas (T).

Given:
Area $A = 20 cm^2 = 20 \times (10^{-2} m)^2 = 20 \times 10^{-4}