diff --git a/_psets/5.md b/_psets/5.md
index 80d653ece8759db8e814a39bc48f2803203ee49a..40f3eb62afb1852ffd56beb11bd1a9d9320cfd78 100644
--- a/_psets/5.md
+++ b/_psets/5.md
@@ -8,22 +8,43 @@ title: Problem Set 5
 Cables designed to carry signals with minimum pickup of interference often consist of a twisted pair
 of conductors surrounded by a grounded shield. Why the twist? Why the shield?
 
-Twisted pairs are used for differential signaling, i.e. where we listen to the difference between
-the voltages on the wires as opposed to either absolute value. Noise can be imparted to our
-conductors by external electric or magnetic fields. In particular, we need to worry about changing
-fields (since static electric fields won't affect our current, and static magnetic fields will
-induce a [Hall effect](https://en.wikipedia.org/wiki/Hall_effect) but not overlay a different
-signal.)
-
-If they were weren't twisted, a close noise source would add more noise to the closer wire, thus
-distorting the voltage difference. Twisting distributes noise on average evenly across the two
-wires, helping preserve the differential signal.
-
-A shield helps prevent noise sources from interacting with the conductors at all. As we've seen,
-oscillating electric fields can only penetrate so far. So the shield effectively provides a low pass
-filter for the sorts of noise that can reach the conducting pair, with the cutoff frequency
-determined by the shield's thickness. Grounding it ensures that built up static charge has a place
-to go, though not all shields are grounded.
+Let's answer this from the ground up. The simplest way to transfer a signal is to use a single wire,
+where a voltage is applied at one end and measured at the other. In practice this requires at least
+some current flow, so there must be a return path which for now I'll assume is literal ground. The
+voltage we measure will be different than the voltage we apply if and only if the path integral of
+the electric field along our wire is nonzero.
+
+A stationary electric field won't have any effect, since it will quickly induce a charge
+distribution that cancels itself (i.e. the field inside a conductor is zero). But a quickly changing
+one can induce a voltage, since the rate of charge transfer within the conductor is finite. This is
+capacitive coupling.
+
+Similarly, a stationary magnetic field will only apply a net force on electrons perpendicular to the
+current. This induces a [Hall effect](https://en.wikipedia.org/wiki/Hall_effect) but won't impact
+our measurement. But a varying magnetic field (or moving the wire through a fixed one) can induce a
+voltage because it causes curl in the electric field. This is inductive coupling.
+
+How can we mitigate these effects? If we surround our signal wire with another conductor, the
+capacitively induced voltages will mostly appear there. This is a shield. The effectiveness of the
+shield depends on its conductivity, its thickness, and the frequency of the interference (recall
+that oscillating electric fields penetrate conductors up to a skin depth). It doesn't necessarily
+need to be grounded to do its job, but doing so ensures it can source enough charge to counteract
+even the strongest external fields, and dissipate static buildup.
+
+The inductive coupling is minimized by minimizing the magnetic flux between our signal wire and the
+current return path. So if we use a second wire for our return path, and keep it next to the first,
+there's much less area for flux to penetrate. By twisting the pair of wires, we create alternating
+regions where the flux will have opposite sign. This causes inductively coupled signals to cancel
+themselves out. If we want to take this even further, we could use
+[star quad](https://en.wikipedia.org/wiki/Star_quad_cable) wire.
+
+Continuing with the theme of noise cancellation, if the drive, line, and load impedances are matched
+in the two wires, then any noise signals that do couple will tend to cause equal voltage
+fluctuations. This is why differential signaling is common. Note that this works even if we don't
+put equal and opposite voltages on the wires: we just need matching electrical characteristics (and
+the assumption of equal noise patterns). But applying equal and opposite voltages to the wires does
+help in another way: it causes the fields generated by our wires to cancel each other out except at
+small distances, so it helps our wires not induce noise in any other signal lines.
 
 
 ## (7.2)