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?

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

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?

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

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

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

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