Which device uses ac current to operate?

the items you connect to a household outlet.

Explanation:

There exists many devices that uses AC current to operate. For example:

1. Electric Clocks. Synchronous clocks rely on the 50 or 60 Hz utility frequency of the AC electric power grid as a timing source. There are cases in which Power Plants decreases its frequency (Most of the times because of a failure), and for that reason you will find that electric clocks are delayed.

2. Fridge. Yes, your fridge needs AC current to work, that's why it's connected to your outlet!

3. Microwave. Yes, also your microwave needs AC current to work.

Basically, all of the items you connect to an outlet works with AC current.

temp rises, and expansion

this could be newton#'s law of cooling. the cooling curve is exponential