From 92202eac9dd94ad4bb9a3ca07b648cd3eab1d982 Mon Sep 17 00:00:00 2001
From: Erik Strand <erik.strand@cba.mit.edu>
Date: Wed, 13 Mar 2019 22:31:03 -0400
Subject: [PATCH] Answer 7.2

---
 _psets/5.md | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/_psets/5.md b/_psets/5.md
index a5aa5c0..d3a8df0 100644
--- a/_psets/5.md
+++ b/_psets/5.md
@@ -28,6 +28,14 @@ to go, though not all shields are grounded.
 
 Salt water has a conductivity ∼4 S/m. What is the skin depth at $$10^4$$ Hz?
 
+$$
+\begin{align*}
+\delta &= \frac{1}{\sqrt{\pi \nu \mu \sigma}} \\
+&= \frac{1}{\sqrt{\pi \cdot 10^4 \si{Hz} \cdot \num{1.3e-6} \si{H/m} \cdot 4 \si{S/m}}} \\
+&= 2.5 \si{m}
+\end{align*}
+$$
+
 ## (7.3)
 
 Integrate Poynting’s vector $$P = E \times H$$ to find the power flowing across a cross-sectional
-- 
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