Are there other quantities besides voltage and current that can be expressed as instantaneous values in AC circuits?

https://www.electrical4u.com/emf-equation-of-transformer-turns-voltage-transformation-ratio-of-transformer/

I got really confused when all of a sudden they treated flux with the time domain equation notation. This is my first time seeing this. My question is simple, are there other quantities besides voltage and current that can be expressed as such in AC circuits? I just got curious would like to be exposed to the idea or not confined that only voltage and current exist in such a manner.

This is in the context of AC circuits because in general probably you could put any quantity in the y-axis and make a sinusoid and say it can. I want to see quantities that are related to AC circuits and may have some application.

• Power is another example Jan 30, 2021 at 14:09
• In non-linear circuits, impedance can be an instantaneous value because it may be a function of voltage or current. Jan 30, 2021 at 14:13
• It's beyond my skill level to make those formulas but impedance would be one and even resistance has instantaneous values if you take thermals into account, like in a tungsten filament.
– K H
Jan 31, 2021 at 10:19
• Well beyond my skill level for transistor amplifiers and stuff anyway. I guess I could do an op amp.
– K H
Jan 31, 2021 at 10:19