Question
A form of “sensing” based on measuring changes in this quantity is used in proximity sensors, liquid level sensors, and theremins. For 10 points each:
[10m] Phone touchscreens work by measuring localized increases in what quantity where your finger touches the screen?
ANSWER: capacitance [accept capacitive sensing; prompt on C]
[10e] In capacitive sensors, changes in capacitance can be detected by measuring charging times or changes in this quantity for a downstream oscillator, since it equals one over root-LC. For US power systems, this quantity's standard operating value is 60 hertz.
ANSWER: frequency [or angular frequency; accept AC frequency]
[10h] Capacitance changes can also be accurately measured by circuits with this topology. AC circuits with this topology, such as ones named for Maxwell, are balanced when they obey the condition “Z1 over Z2 equals Z3 over Z4.”
ANSWER: bridge circuits [accept Maxwell bridges; prompt on lattice circuits]
<VD, Physics>
Summary
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