If you want to built simple audio amplifier without messy components then you can construct simple single transistor audio amplifier circuit using BC547 and Resistor, Capacitor. This circuit can drive 8 ohm loud speaker and produce considerable sound. Apply 9 Volt DC supply for better result. Two types of single transistor audio amplifier circuit designed with BC 547 transistor, here first one ... Activity 1: Simple Circuits For an electric current to flow through the light bulb, the battery must be connected to the bulb to form a complete circuit as illustrated below. These circuit lessons for elementary and middle school students are fun to make. We've included printable PDF worksheets for electricity and lesson plans for teachers from PBS and Duke Energy. There is also a free online circuit lesson from Brainpop. Scroll down to get your own Circuit Building Kit. Enjoy!