Update em.ipynb

chapter3/em.ipynb

@@ -44,7 +44,7 @@
     "\n",
     "which holds for an isotropic linear magnetic medium.\n",
     "Here, $\\mu$ is the magnetic permability of the material.\n",
-    "Now, since $B$ is solenodial (divergence free) accoording to Maxwell's equations, we known that $B$ must be the curl of some vector field $A$. This field is called the magnetic vector potential. Since the problem is static and thus $\\frac{\\partial D}{\\partial t}=0$, it follows that\n",
+    "Now, since $B$ is solenodial (divergence free) according to Maxwell's equations, we known that $B$ must be the curl of some vector field $A$. This field is called the magnetic vector potential. Since the problem is static and thus $\\frac{\\partial D}{\\partial t}=0$, it follows that\n",
     "\n",
     "$$\n",
     "J = \\nabla \\times H = \\nabla \\times(\\mu^{-1} B)=\\nabla \\times (\\mu^{-1}\\nabla \\times A ) = -\\nabla \\cdot (\\mu^{-1}\\nabla A).\n",