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Figure $$\PageIndex{1}$$: This circuit shown is used to amplify small signals and power the earbud speakers attached to a cellular phone. This circuit’s components include resistors, capacitors, and diodes, all of which have been covered in previous chapters, as well as transistors, which are semi-conducting devices covered in Condensed Matter Physics. Circuits using similar components are found in all types of equipment and appliances you encounter in everyday life, such as alarm clocks, televisions, computers, and refrigerators. (credit: Jane Whitney)