diff --git a/docs/1b/ece140.md b/docs/1b/ece140.md
index 25a6979..bc0a8b0 100644
--- a/docs/1b/ece140.md
+++ b/docs/1b/ece140.md
@@ -25,7 +25,7 @@ $$i=\frac{dq}{dt}\approx \frac{\Delta q}{\Delta t}$$
### Power
-Power represents the rate of doing work, in unit watts ($\pu W$, J/s)
+Power represents the rate of doing work, in unit watts ($\pu W$, \pu{J/s})
$$P=\frac{dw}{dt}$$
@@ -37,4 +37,37 @@ Much like relative velocity, power is directional and relative, with a positive
$$P_{CB}=-P_{BC}$$
+In a closed system, conservation of energy applies:
+
+$$\sum P_\text{in}=\sum P_\text{out}$$
+
The **ground** is the "absolute zero" voltage with a maximum potential difference. It is also known as the "reference voltage".
+
+### Independent energy sources
+
+!!! definition
+ - A **ground** is the reference point that all **potential differences are relative to**.
+
+A **generic voltage source** provides a known potential difference between its two terminals that is defined by the source. The resultant current can be calculated.
+
+
(Source: Wikimedia Commons)
+
+A **generic current source** provides a known amperage between its two terminals that is defined by the source. The resultant voltage can be calculated.
+
+
(Source: Wikimedia Commons)
+
+!!! tip
+ A current in the **positive direction** indicates that the source is releasing power (is a source). Otherwise, it is consuming power (is a load).
+
+### Dependent energy sources
+
+A **dependent <T: voltage | current> source** has a **T** dependent on the voltage or current elsewhere in the circuit. $k$ is a function that is likely but not guaranteed to be linear.
+
+$$
+v=kv_0\ |\ ki_0 \\
+i=kv_0\ |\ ki_0
+$$
+
+
(Source: Wikimedia Commons)
+
+
(Source: Wikimedia Commons)