By Cathleen Shamieh

Capacitors are extremely useful in electronics and, chances are, you’ve used them many times without realizing it. Here are some places where you may have met up with capacitors:

  • Alarm clocks: Many alarm clocks keep charged capacitors on hand in case there’s a power failure. When the power goes out, the capacitor discharges — sending current through the clock circuit to keep the circuit running.
  • Smartphone screens: Your body has a certain amount of capacitance, meaning that it can (and does) store some electric charge. If you touch the screen of nearly any smartphone (except really old ones), tiny electronic circuits inside the phone sense the stored charges in your finger. The circuits figure out what part of the screen you’re touching and use that information to determine what you want the smartphone to do. This type of screen is known as a capacitive touchscreen.
  • Power converters: Capacitors are also used in circuits that convert alternating current (AC) — which alternates between flowing forward and backward — to direct current (DC) — which flows in only one direction. The wall sockets in your home and school provide AC power, but your TV, stereo, computers, tablets, phones, and many other electronic devices need DC power to operate. Circuitry in the device itself or in an external power converter that plugs into the device (for instance, a smartphone charger) transforms the AC power into DC power, and capacitors are an important part of that circuitry.

  • Stereo systems: If you’ve ever adjusted the treble (high-pitched) or bass (low-pitched) sounds in your family’s car or home stereo system, you’ve used capacitors to change the sound of your music. Capacitors are used in special circuits called filters to boost or lower certain sounds in the music. So if you like to emphasize, say, the drums in the music you listen to, you turn up the bass and turn down the treble. Capacitors and other components inside the stereo are what make it possible for you to do this.