first order differential equation application in ECE

Can anyone help me?! I'm looking for a sample application with problem and equation for the 1st Order Differential Equation for Electronic Comunication Engineering Course.

Simple or Complex..

The Following applications are already given by our proffesor so we cannot use that as a sample..

Exponential Growth - Population

Exponential Decay - Radioactive Material

Falling Object

Newton's Law of Cooling

RL circuit

Hope you guys can help me.. Thank You