Every electronic device you own is full of tiny parts called resistors. These resistors help protect the sensitive chips inside your phone, computer, and camera. They're the reason why your devices become hot to the touch as they’re charging. Without resistors, none of the electronics in your life would work.
Currents and Volts
Ohm's law describes how electricity flows through a wire. According to German physicist Georg Ohm, the current, or the rate of the flow of electric charge, is equal to the voltage divided by the resistance. Resistance slows down the current. In most devices, engineers use multiple resistors to slow down the current as it races through the wires. The resistors reduce the current by turning some of the electrical energy into heat energy. When a resistor is working, it becomes hot. As engineers add resistors to a circuit, the rational expression for voltage divided by resistance can get quite complicated. Regardless, the current has to be calculated accurately in order to protect sensitive parts.
When you charge your phone, its resistors go into action. They make sure that the charge doesn't damage sensitive hardware. If a resistor overheats, it breaks. However, this break also breaks the circuit and stops the flow of electricity. This means that an overloaded resistor won't damage the rest of your phone. Without resistors, we wouldn't be able to use technology like touch screens or LED lights. We wouldn't be able to listen to music or even use a blender. Even our cars depend on resistors. By understanding how resistors work, you can learn to troubleshoot the machines that surround us.
See for yourself: http://www.youtube.com/watch?v=VPVoY1QROMg
Watch the first clip below for more on Ohm's law. Check out the following videos to learn how to replace a car's blower resistor or a broken DC jack in a laptop that won't charge.