Expand knowledge base

1 files changed, 10 insertions, 1 deletions

diff --git a/content/know/concept/wentzel-kramers-brillouin-approximation/index.pdc b/content/know/concept/wentzel-kramers-brillouin-approximation/index.pdc
index 482650e..cf44fc8 100644
--- a/content/know/concept/wentzel-kramers-brillouin-approximation/index.pdc
+++ b/content/know/concept/wentzel-kramers-brillouin-approximation/index.pdc
@@ -14,7 +14,7 @@ markup: pandoc
 # Wentzel-Kramers-Brillouin approximation
 
 In quantum mechanics, the **Wentzel-Kramers-Brillouin** or simply the **WKB
-approximation** is a method to approximate the wave function $\psi(x)$ of
+approximation** is a technique to approximate the wave function $\psi(x)$ of
 the one-dimensional time-independent Schrödinger equation. It is an example
 of a **semiclassical approximation**, because it tries to find a
 balance between classical and quantum physics.
@@ -196,3 +196,12 @@ In the classical region ($E > V$), the wave function oscillates, and
 in the quantum-mechanical region ($E < V$) it is exponential. Note that for
 $E \approx V$ the approximation breaks down, due to the appearance of
 $p(x)$ in the denominator.
+
+
+## References
+1.  D.J. Griffiths, D.F. Schroeter,
+    *Introduction to quantum mechanics*, 3rd edition,
+    Cambridge.
+2.  R. Shankar,
+    *Principles of quantum mechanics*, 2nd edition,
+    Springer.