diff --git a/src/4_sommerfeld_model.md b/src/4_sommerfeld_model.md
index a93a446570e03cc10a7e3d72cd4ef9302e8cb21e..0ce00ad2d4abc97f34fe5ad204a68c27430e1eb8 100644
--- a/src/4_sommerfeld_model.md
+++ b/src/4_sommerfeld_model.md
@@ -220,7 +220,7 @@ ax.set_xlabel(r"$\varepsilon$")
 draw_classic_axes(ax, xlabeloffset=.2)
 ```
 
-Electrons in the top triangle are being excited to the bottom triangle due to temperature increase. Number of excited electrons $\approx\frac{1}{4}g(\varepsilon_{\rm F})k_{\rm B}T=n_{\rm exc}$. Total extra energy $E(T)-E(0)=n_{\rm exc}k_{\rm B}T=\frac{1}{2}g(\varepsilon_{\rm F})k_{\rm B}^2T^2$.
+Electrons in the top triangle are being excited to the bottom triangle due to temperature increase. Number of excited electrons $\approx\frac{1}{4}g(\varepsilon_{\rm F})k_{\rm B}T=n_{\rm exc}$. Total extra energy $E(T)-E(0)=n_{\rm exc}k_{\rm B}T=\frac{1}{4}g(\varepsilon_{\rm F})k_{\rm B}^2T^2$.
 
 $$
 C_{V,e}=\frac{ {\rm d}E}{ {\rm d}T}=\frac{1}{2}g(\varepsilon_{\rm F})k_{\rm B}^2T=\ ...\ =\frac{3}{4}Nk_{\rm B}\frac{T}{T_{\rm F}}\propto T