26.2 - Interactive checkpoint: the fuel-cell car
Honda’s FCX fuel-cell automobile uses a custom built, 8.00-farad ultracapacitor that provides power in faster bursts than a fuel cell can deliver
on its own, allowing the car to accelerate quickly.
The ultracapacitor is charged by both the car’s fuel cell and energy recovered each time the car brakes. Together, these energy sources can
be used to provide a potential difference of 200 V across the capacitor electrodes (plates).How much charge does an 8.00-farad
ultracapacitor accumulate when it is
charged with a potential difference of
200 V?
Answer:q = C
26.3 - Physics at work: capacitors and computer keyboards
Your computer keyboard may contain capacitors. In
some types of keyboards, each key sits above its own
capacitor. Although more expensive to produce than
those based on other designs, capacitor based
keyboards are more reliable. The bottom part of the
capacitor is fixed, and the top is a movable plate. A
springy insulating material separates the plates. As
you press down on a key, the two plates of its
capacitor are pushed closer together. Since this
changes the geometry of the capacitor, it also
changes the capacitance: Specifically, it increases it.
A microprocessor in the keyboard interprets the
change in capacitance as a signal that the key has been pressed.
The keyboard microprocessor relays this information to the computer’s central
processing unit, which responds to it according to which application is running. For
example, a word processor might display the keystroke as a character, while a game
might interpret it as a command for a player to shoot a basketball.Computer keyboards
Keystroke reduces distance between
plates
Microprocessor detects changed
capacitance(^478) Copyright 2000-2007 Kinetic Books Co. Chapter 26