How do Touchscreens work?
Electronic devices can use lots of different methods to detect a person's input on a touchscreen. Most of them use sensors and circuitry to monitor changes in a particular state. Many like the iPhone's, monitor changes in electrical current.
Apple iPad ad - Together (2013)
What is a touchscreen?
A touch screen is a device you can control with the touch of your finger(s). some touchscreens can sense the touch of a stylus or specially designed gloves. The touchscreen enables the user to interact directly with what is displayed, rather than using a mouse, touchpad, or any other intermediate device.