# A-level Physics (Advancing Physics)/Flux/Worked Solutions

1. A circular steel core has a cross-sectional area of 9 cm2, and a length of 0.5m. If the permeability of steel is 875 μNA−2., what is the permeance of the core?

${\displaystyle \Lambda ={\frac {\mu A}{L}}={\frac {875\times 10^{-6}\times 9\times 10^{-4}}{0.5}}=1.58{\mbox{ }}\mu {\mbox{WbA}}^{-1}}$

2. A coil of insulated wire is wrapped 60 times around the top of the core, and a 9A direct current is put through the coil. How much flux is induced?

${\displaystyle \Phi =\Lambda NI=1.58\times 10^{-6}\times 60\times 9=0.851{\mbox{ mWb}}}$

3. Assuming that all the flux goes through the core, what is the flux density at any point in the core?

${\displaystyle B={\frac {\Phi }{A}}={\frac {0.851\times 10^{-3}}{9\times 10^{-4}}}=0.945{\mbox{ Wbm}}^{-2}}$

4. Draw a diagram showing the lines of flux within the core.