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 &mu;NA−2., what is the permeance of the core?'''

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

'''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?'''

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

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

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

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