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# Doctor Who Season 2 Episode 3 "School Reunion"

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So in the third episode of the second season of Doctor Who, the Tenth Doctor had a brief stint as a physics teacher. To clarify, the man with the glasses is the Tenth Doctor, not be confused with the Eleventh Doctor who was in the last post.

Anyways, he asks the class some questions to test their knowledge. One question was this: "I coil up a thin piece of nichrome wire and place it in a glass of water, then I turn on the electricity and measure to see if the water temperature's affected.

My question is this - how do I measure the electrical power going into the coil?"

He responds that power can be measured "...using an ammeter and a voltmeter." But how exactly is that? You probably already know but I'm going to explain it anyway. The ammeter measures for current and the voltmeter measures for- you guessed it- voltage. Electrical power is equal to current times voltage (P=IV). If you measure the voltage and current going through the wire, you can calculate the electrical power the system is generating.

If you wanted the energy dissipated by the system, the electrical energy equals power times time. That means you would need a time interval for this to be occurring on (like 2 minutes or something like that). Eventually this could be used to find the energy transferred to the water and after that the temperature of the water after the system has acted on the it

over that time.

So to recap:

(Yes, this is my icon and now it has been explained!)

All of these gifs are from the actual episode as well, I haven't edited any of them. This was a pretty basic physics question, but important none the less.

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