Week 24: Dimming Up and Dimming Down

In the 2005 movie Bewitched with Nicole Kidman and Will Ferrell, there's a roll of different clips where Samantha settles into her new life. She moves into her new house and cleans it up, she has quite a bit of trouble setting up her TV, I think, and she even opens tons of cans of soda because she had always opened them by magic. Buy my favorite part of the montage is when Samantha discovers that her dining room lights have a dimmer switch and she has a bit of fun slowly making it brighter, then dimmer, then brighter and so on. And all the while she does this, she goes, "Dimming uuuupppppp....dimming doooowwwwwnnnn..."

That part always makes me smile.

We actually have a dimmer switch on the lights above our dining table.



"Undimmed"

Dimmed

 

The brightness of the lights depend on the power or the amount of current that flows through them. The higher the current, the higher the power and the brighter the lights. Therefore, moving the switch up and down changes the magnitude of flowing current.

But how does it do this? Inside the dimmer switch is a moving variable resistor. This is basically a piece of metal that can increase the distance that the charge has to travel.

As I move the switch up to dim the lights, the length (L) that the charge has to travel increases. The resistance of the metal (R), or the metal's ability to oppose the electric flow, increases as L increases.

As R increases, I decreases because the two are inversely proportional. As I decreases, power (P) decreases as well because the two are directly proportional.

Finally, as P decreases, the lights dim down.

And, voila, the Physics of "dimming uuuupppppp....dimming doooowwwwwnnnn...!"